Subjects -> PHYSICS (Total: 857 journals)
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THERMODYNAMICS (30 journals)

Showing 1 - 29 of 29 Journals sorted alphabetically
Advances in Heat Transfer     Full-text available via subscription   (Followers: 26)
Applied Thermal Engineering     Hybrid Journal   (Followers: 41)
Araucaria. Revista Iberoamericana de Filosofía, Política y Humanidades     Open Access  
Archives of Thermodynamics     Open Access   (Followers: 9)
Chemical Thermodynamics and Thermal Analysis     Open Access   (Followers: 7)
Condensed Matter Physics     Open Access   (Followers: 2)
Diffusion Foundations     Full-text available via subscription   (Followers: 4)
European Journal of Mechanics - B/Fluids     Hybrid Journal   (Followers: 5)
Experimental Heat Transfer     Hybrid Journal   (Followers: 17)
Experimental Thermal and Fluid Science     Hybrid Journal   (Followers: 34)
Fluids     Open Access   (Followers: 1)
Heat and Mass Transfer     Hybrid Journal   (Followers: 28)
Heat Transfer Engineering     Hybrid Journal   (Followers: 37)
High Temperature     Hybrid Journal   (Followers: 2)
HTM Journal of Heat Treatment and Materials     Full-text available via subscription   (Followers: 3)
International Journal of Thermodynamics     Open Access   (Followers: 11)
International Journal of Thermophysics     Hybrid Journal   (Followers: 7)
Journal of Thermodynamics & Catalysis     Open Access   (Followers: 6)
Journal of Chemical Thermodynamics     Hybrid Journal   (Followers: 4)
Journal of Low Temperature Physics     Hybrid Journal   (Followers: 8)
Journal of Non-Newtonian Fluid Mechanics     Hybrid Journal   (Followers: 16)
Journal of Thermal Science     Hybrid Journal   (Followers: 21)
Journal of Thermal Spray Technology     Hybrid Journal   (Followers: 5)
Journal of Thermodynamics     Open Access   (Followers: 7)
Journal of Thermophysics and Heat Transfer     Hybrid Journal   (Followers: 93)
Low Temperature Physics     Hybrid Journal   (Followers: 6)
Metal Science and Heat Treatment     Hybrid Journal   (Followers: 36)
Quantitative InfraRed Thermography Journal     Hybrid Journal  
Thermophysics and Aeromechanics     Hybrid Journal   (Followers: 6)
Similar Journals
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Fluids
Number of Followers: 1  

  This is an Open Access Journal Open Access journal
ISSN (Online) 2311-5521
Published by MDPI Homepage  [258 journals]
  • Fluids, Vol. 9, Pages 52: Influence of Cross Perturbations on Turbulent
           Kelvin–Helmholtz Instability

    • Authors: Mae Sementilli, Rozie Zangeneh, James Chen
      First page: 52
      Abstract: Kelvin–Helmholtz instability has been studied extensively in 2D. This study attempts to address the influence of turbulent flow and cross perturbation on the growth rate of the instability and the development of mixing layers in 3D by means of direct numerical simulation. Two perfect gases are considered to be working fluids moving as opposite streams, inducing shear instability at the interface between the fluids and resulting in Kelvin–Helmholtz instability. The results show that cross perturbation affects the instability by increasing the amplitude growth while adding turbulence has almost no effect on the amplitude growth. Furthermore, by increasing the turbulence intensity, a more distinct presence of the inner flow can be seen in the mixing layer of the two phases, and the presence of turbulence expands the range of high-frequency motion significantly due to turbulence structures. The results give a basis for which 3D Kelvin–Helmholtz phenomena should be further investigated using numerical simulation for predictive modeling, beyond the use of simplified 2D theoretical models.
      Citation: Fluids
      PubDate: 2024-02-20
      DOI: 10.3390/fluids9030052
      Issue No: Vol. 9, No. 3 (2024)
       
  • Fluids, Vol. 9, Pages 53: Application of a Combinatorial Vortex Detection
           Algorithm on 2 Component 2 Dimensional Particle Image Velocimetry Data to
           Characterize the Wake of an Oscillating Wing

    • Authors: Mathew Bussière, Guilherme M. Bessa, Charles R. Koch, David S. Nobes
      First page: 53
      Abstract: To investigate the vortical wake pattern generated by water flow past an oscillating symmetric airfoil, using experimental velocity fields from particle image velocimetry (PIV), a novel combinatorial vortex detection (CVD) algorithm is developed. The primary goal is to identify and characterize vortices within the wake. Experimental flows introduce complexities not present in numerical simulations, posing challenges for vortex detection. The proposed CVD approach offers a more robust alternative, excelling in both vortex detection and quantification of essential parameters, unlike widely-used methods such as Q-criterion, λ2-criterion, and Δ-criterion, which rely on subjective and arbitrary thresholds resulting in uncertainty. The CVD algorithm effectively characterizes the airfoil wake, identifying and analyzing vortices aligning with the Burgers model. This research enhances understanding of wake phenomena and showcases the algorithm’s potential as a valuable tool for vortex detection and characterization, particularly for experimental fluid dynamics. It provides a comprehensive, robust, and non-arbitrary approach, overcoming limitations of traditional methods and opening new avenues for studying complex flows.
      Citation: Fluids
      PubDate: 2024-02-22
      DOI: 10.3390/fluids9030053
      Issue No: Vol. 9, No. 3 (2024)
       
  • Fluids, Vol. 9, Pages 54: Airborne Transmission of SARS-CoV-2: The
           Contrast between Indoors and Outdoors

    • Authors: Clive B. Beggs, Rabia Abid, Fariborz Motallebi, Abdus Samad, Nithya Venkatesan, Eldad J. Avital
      First page: 54
      Abstract: COVID-19 is an airborne disease, with the vast majority of infections occurring indoors. In comparison, little transmission occurs outdoors. Here, we investigate the airborne transmission pathways that differentiate the indoors from outdoors and conclude that profound differences exist, which help to explain why SARS-CoV-2 transmission is much more prevalent indoors. Near- and far-field transmission pathways are discussed along with factors that affect infection risk, with aerosol concentration, air entrainment, thermal plumes, and occupancy duration all identified as being influential. In particular, we present the fundamental equations that underpin the Wells–Riley model and show the mathematical relationship between inhaled virus particles and quanta of infection. A simple model is also presented for assessing infection risk in spaces with incomplete air mixing. Transmission risk is assessed in terms of aerosol concentration using simple 1D equations, followed by a description of thermal plume–ceiling interactions. With respect to this, we present new experimental results using Schlieren visualisation and computational fluid dynamics (CFD) based on the Eulerian–Lagrangian approach. Pathways of airborne infection are discussed, with the key differences identified between indoors and outdoors. In particular, the contribution of thermal and exhalation plumes is evaluated, and the presence of a near-field/far-field feedback loop is postulated, which is absent outdoors.
      Citation: Fluids
      PubDate: 2024-02-22
      DOI: 10.3390/fluids9030054
      Issue No: Vol. 9, No. 3 (2024)
       
  • Fluids, Vol. 9, Pages 55: Computational Flow Diverter Implantation—A
           Comparative Study on Pre-Interventional Simulation and Post-Interventional
           Device Positioning for a Novel Blood Flow Modulator

    • Authors: Maximilian Thormann, Janneck Stahl, Laurel Marsh, Sylvia Saalfeld, Nele Sillis, Andreas Ding, Anastasios Mpotsaris, Philipp Berg, Daniel Behme
      First page: 55
      Abstract: Due to their effect on aneurysm hemodynamics, flow diverters (FD) have become a routine endovascular therapy for intracranial aneurysms. Since over- and undersizing affect the device’s hemodynamic abilities, selecting the correct device diameter and accurately simulating FD placement can improve patient-specific outcomes. The purpose of this study was to validate the accuracy of virtual flow diverter deployments in the novel Derivo® 2 device. We retrospectively analyzed blood flows in ten FD placements for which 3D DSA datasets were available pre- and post-intervention. All patients were treated with a second-generation FD Derivo® 2 (Acandis GmbH, Pforzheim, Germany) and post-interventional datasets were compared to virtual FD deployment at the implanted position for implanted stent length, stent diameters, and curvature analysis using ANKYRAS (Galgo Medical, Barcelona, Spain). Image-based blood flow simulations of pre- and post-interventional configurations were conducted. The mean length of implanted FD was 32.61 (±11.18 mm). Overall, ANKYRAS prediction was good with an average deviation of 8.4% (±5.8%) with a mean absolute difference in stent length of 3.13 mm. There was a difference of 0.24 mm in stent diameter amplitude toward ANKYRAS simulation. In vessels exhibiting a high degree of curvature, however, relevant differences between simulated and real-patient data were observed. The intrasaccular blood flow activity represented by the wall shear stress was qualitatively reduced in all cases. Inflow velocity decreased and the pulsatility over the cardiac cycle was weakened. Virtual stenting is an accurate tool for FD positioning, which may help facilitate flow FDs’ individualization and assess their hemodynamic impact. Challenges posed by complex vessel anatomy and high curvatures must be addressed.
      Citation: Fluids
      PubDate: 2024-02-23
      DOI: 10.3390/fluids9030055
      Issue No: Vol. 9, No. 3 (2024)
       
  • Fluids, Vol. 9, Pages 56: Computation of Real-Fluid Thermophysical
           Properties Using a Neural Network Approach Implemented in OpenFOAM

    • Authors: Nasrin Sahranavardfard, Damien Aubagnac-Karkar, Gabriele Costante, Faniry N. Z. Rahantamialisoa, Chaouki Habchi, Michele Battistoni
      First page: 56
      Abstract: Machine learning based on neural networks facilitates data-driven techniques for handling large amounts of data, either obtained through experiments or simulations at multiple spatio-temporal scales, thereby finding the hidden patterns underlying these data and promoting efficient research methods. The main purpose of this paper is to extend the capabilities of a new solver called realFluidReactingNNFoam, under development at the University of Perugia, in OpenFOAM with a neural network algorithm for replacing complex real-fluid thermophysical property evaluations, using the approach of coupling OpenFOAM and Python-trained neural network models. Currently, neural network models are trained against data generated using the Peng–Robinson equation of state assuming a mixture’s frozen temperature. The OpenFOAM solver, where needed, calls the neural network models in each grid cell with appropriate inputs, and the returned results are used and stored in suitable OpenFOAM data structures. Such inference for thermophysical properties is achieved via the “Neural Network Inference in C made Easy (NNICE)” library, which proved to be very efficient and robust. The overall model is validated considering a liquid-rocket benchmark comprised of liquid-oxygen (LOX) and gaseous-hydrogen (GH2) streams. The model accounts for real-fluid thermodynamics and transport properties, making use of the Peng–Robinson equation of state and the Chung transport model. First, the development of a real-fluid model with an artificial neural network is described in detail. Then, the numerical results of the transcritical mixing layer (LOX/GH2) benchmark are presented and analyzed in terms of accuracy and computational efficiency. The results of the overall implementation indicate that the combined OpenFOAM and machine learning approach provides a speed-up factor higher than seven, while preserving the original solver accuracy.
      Citation: Fluids
      PubDate: 2024-02-23
      DOI: 10.3390/fluids9030056
      Issue No: Vol. 9, No. 3 (2024)
       
  • Fluids, Vol. 9, Pages 57: Ten Years of Passion: I.S. Gromeka’s
           Contribution to Science

    • Authors: Kamil Urbanowicz, Arris S. Tijsseling
      First page: 57
      Abstract: The work and life of Ippolit Stepanovich Gromeka is reviewed. Gromeka authored a classical set of eleven papers on fluid dynamics in just ten years before a tragic illness ended his life. Sadly, he is not well known to the western scientific community because all his publications were written in Russian. He is one of the three authors who independently derived an analytical solution for accelerating laminar pipe flow. He was the first to eliminate the contradiction between the theories of Young and Laplace on capillary phenomena. He initiated the theoretical basis of helical (Beltrami) flow, and he studied the movement of cyclones and anticyclones seventeen years before Zermelo (whose work is considered as pioneering). He is also the first to analyse wave propagation in liquid-filled hoses, thereby including fluid–structure interaction.
      Citation: Fluids
      PubDate: 2024-02-23
      DOI: 10.3390/fluids9030057
      Issue No: Vol. 9, No. 3 (2024)
       
  • Fluids, Vol. 9, Pages 58: Visualizing and Evaluating Microbubbles in
           Multiphase Flow Applications

    • Authors: Safa A. Najim, Deepak Meerakaviyad, Kul Pun, Paul Russell, Poo Balan Ganesan, David Hughes, Faik A. Hamad
      First page: 58
      Abstract: Accurate visualization of bubbles in multiphase flow is a crucial aspect of modeling heat transfer, mixing, and turbulence processes. It has many applications, including chemical processes, wastewater treatment, and aquaculture. A new software, Flow_Vis, based on experimental data visualization, has been developed to visualize the movement and size distribution of bubbles within multiphase flow. Images and videos recorded from an experimental rig designed to generate microbubbles were analyzed using the new software. The bubbles in the fluid were examined and found to move with different velocities due to their varying sizes. The software was used to measure bubble size distributions, and the obtained results were compared with experimental measurements, showing reasonable accuracy. The velocity measurements were also compared with literature values and found to be equally accurate.
      Citation: Fluids
      PubDate: 2024-02-27
      DOI: 10.3390/fluids9030058
      Issue No: Vol. 9, No. 3 (2024)
       
  • Fluids, Vol. 9, Pages 59: Application of Deep Learning in Predicting
           Particle Concentration of Gas–Solid Two-Phase Flow

    • Authors: Zhiyong Wang, Bing Yan, Haoquan Wang
      First page: 59
      Abstract: Particle concentration is an important parameter for describing the state of gas–solid two-phase flow. This study compares the performance of three methods, namely, Back-Propagation Neural Networks (BPNNs), Recurrent Neural Networks (RNNs), and Long Short-Term Memory (LSTM), in handling gas–solid two-phase flow data. The experiment utilized seven parameters, including temperature, humidity, upstream and downstream sensor signals, delay, pressure difference, and particle concentration, as the dataset. The evaluation metrics, such as prediction accuracy, were used for comparative analysis by the experimenters. The experiment results indicate that the prediction accuracies of the RNN, LSTM, and BPNN experiments were 92.4%, 92.7%, and 92.5%, respectively. Future research can focus on further optimizing the performance of the BPNN, RNN, and LSTM to enhance the accuracy and efficiency of gas–solid two-phase flow data processing.
      Citation: Fluids
      PubDate: 2024-02-27
      DOI: 10.3390/fluids9030059
      Issue No: Vol. 9, No. 3 (2024)
       
  • Fluids, Vol. 9, Pages 60: Grid Turbulence Measurements with an Acoustic
           Doppler Current Profiler

    • Authors: Trygve K. Løken, David Lande-Sudall, Atle Jensen, Jean Rabault
      First page: 60
      Abstract: The motivation for this study is to investigate the abilities and limitations of a Nortek Signature1000 acoustic Doppler current profiler (ADCP) regarding fine-scale turbulence measurements. Current profilers offer the advantage of gaining more coherent measurement data than available with point acoustic measurements, and it is desirable to exploit this property in laboratory and field applications. The ADCP was tested in a towing tank, where turbulence was generated from a grid towed under controlled conditions. Grid-induced turbulence is a well-studied phenomenon and a good approximation for isotropic turbulence. Several previous experiments are available for comparison and there are developed theories within the topic. In the present experiments, a Nortek Vectrino acoustic Doppler velocimeter (ADV), which is an established instrument for turbulence measurements, was applied to validate the ADCP. It was found that the mean flow measured with the ADCP was accurate within 4% of the ADV. The turbulent variance was reasonably well resolved by the ADCP when large grid bars were towed at a high speed, but largely overestimated for lower towing speed and smaller grid bars. The effective cutoff frequency and turbulent eddy size were characterized experimentally, which provides detailed guidelines for when the ADCP data can be trusted and will allow future experimentalists to decide a priori if the Nortek Signature can be used in their setup. We conclude that the ADCP is not suitable for resolving turbulent spectra in a small-scale grid-induced flow due to the intrinsic Doppler noise and the low spatial and temporal sample resolution relative to the turbulent scales.
      Citation: Fluids
      PubDate: 2024-03-01
      DOI: 10.3390/fluids9030060
      Issue No: Vol. 9, No. 3 (2024)
       
  • Fluids, Vol. 9, Pages 31: Characterization of the Wing Tone around the
           Antennae of a Mosquito-like Model

    • Authors: Yongtao Wang, Zhiteng Zhou, Zhuoyu Xie
      First page: 31
      Abstract: Mosquitoes’ self-generated air movements around their antennae, especially at the wing-beat frequency, are crucial for both obstacle avoidance and mating communication. However, the characteristics of these air movements are not well clarified. In this study, the air movements induced by wing tones (sound generated by flapping wings in flight) around the antennae of a mosquito-like model (Culex quinquefasciatus, male) are investigated using the acoustic analogy method. Both the self-generated wing tone and the wing tone reflected from the ground are calculated. Given that the tiny changes in direction and magnitude of air movements can be detected by the mosquito’s antennae, a novel method is introduced to intuitively characterize the air movements induced by the wing tone. The air movements are decomposed into two basic modes (oscillation and revolution). Our results show that, without considering the scattering on the mosquito’s body, the self-generated sound wave of the wing-beat frequency around the antennae mainly induces air oscillation, with the velocity amplitude exceeding the mosquito’s hearing threshold of the male wingbeat frequency by two orders of magnitude. Moreover, when the model is positioned at a distance from the ground greater than approximately two wing lengths, the reflected sound wave at the male wingbeat frequency attenuates below the hearing threshold. That is, the role of reflected wing tone in the mosquito’s obstacle avoidance mechanism appears negligible. Our findings and method may provide insight into how mosquitoes avoid obstacles when their vision is unavailable and inspire the development of collision avoidance systems in micro-aerial vehicles.
      Citation: Fluids
      PubDate: 2024-01-24
      DOI: 10.3390/fluids9020031
      Issue No: Vol. 9, No. 2 (2024)
       
  • Fluids, Vol. 9, Pages 32: Numerical Investigation of Gas Bubble
           Interaction in a Circular Cross-Section Channel in Shear Flow

    • Authors: Daniel B. V. Santos, Gustavo P. Oliveira, Norberto Mangiavacchi, Prashant Valluri, Gustavo R. Anjos
      First page: 32
      Abstract: This work’s goal is to numerically investigate the interactions between two gas bubbles in a fluid flow in a circular cross-section channel, both in the presence and in the absence of gravitational forces, with several Reynolds and Weber numbers. The first bubble is placed at the center of the channel, while the second is near the wall. Their positions are set in such a way that a dynamic interaction is expected to occur due to their velocity differences. A finite element numerical tool is utilized to solve the incompressible Navier–Stokes equations and simulate two-phase flow using an unfitted mesh to represent the fluid interface, akin to the front-tracking method. The results show that the velocity gradient influences bubble shapes near the wall. Moreover, lower viscosity and surface tension force account for more significant interactions, both in the bubble shape and in the trajectory. In this scenario, it can be observed that one bubble is trapped in the other’s wake, with the proximity possibly allowing the onset of coalescence. The results obtained contribute to a deeper understanding of two-phase inner flows.
      Citation: Fluids
      PubDate: 2024-01-26
      DOI: 10.3390/fluids9020032
      Issue No: Vol. 9, No. 2 (2024)
       
  • Fluids, Vol. 9, Pages 33: Application of Central-Weighted Essentially
           Non-Oscillatory Finite-Volume Interface-Capturing Schemes for Modeling
           Cavitation Induced by an Underwater Explosion

    • Authors: Ebenezer Mayowa Adebayo, Panagiotis Tsoutsanis, Karl W. Jenkins
      First page: 33
      Abstract: Cavitation resulting from underwater explosions in compressible multiphase or multicomponent flows presents significant challenges due to the dynamic nature of shock–cavitation–structure interactions, as well as the complex and discontinuous nature of the involved interfaces. Achieving accurate resolution of interfaces between different phases or components, in the presence of shocks, cavitating regions, and structural interactions, is crucial for modeling such problems. Furthermore, pressure convergence in simulations involving shock–cavitation–structure interactions requires accurate algorithms. In this research paper, we employ the diffuse interface method, also known as the interface-capturing scheme, to investigate cavitation in various underwater explosion test cases near different surfaces: a free surface and a rigid surface. The simulations are conducted using the unstructured compressible Navier–Stokes (UCNS3D) finite-volume framework employing central-weighted essentially non-oscillatory (CWENO) reconstruction schemes, utilizing the five-equation diffuse interface family of methods. Quantitative comparisons are made between the performance of both models. Additionally, we examine the effects of cavitation as a secondary loading source on structures, and evaluate the ability of the CWENO schemes to accurately capture and resolve material interfaces between fluids with minimal numerical dissipation or smearing. The results are compared with existing high-order methods and experimental data, where possible, to demonstrate the robustness of the CWENO schemes in simulating cavitation bubble dynamics, as well as their limitations within the current implementation of interface capturing.
      Citation: Fluids
      PubDate: 2024-01-29
      DOI: 10.3390/fluids9020033
      Issue No: Vol. 9, No. 2 (2024)
       
  • Fluids, Vol. 9, Pages 34: The Chimera Revisited: Wall- and
           Magnetically-Bounded Turbulent Flows

    • Authors: Nils Tångefjord Basse
      First page: 34
      Abstract: This review is a first attempt at bringing together various concepts from research on wall- and magnetically-bounded turbulent flows. Brief reviews of both fields are provided: The main similarities identified are coherent (turbulent) structures, flow generation, and transport barriers. Examples are provided and discussed.
      Citation: Fluids
      PubDate: 2024-01-30
      DOI: 10.3390/fluids9020034
      Issue No: Vol. 9, No. 2 (2024)
       
  • Fluids, Vol. 9, Pages 35: An Experimental Study on the Effect of Distance
           and Sheltering Area of a Group of Linearly Arranged Sacrificial Piles on
           Reducing Local Scour around a Circular Bridge Pier under Clear-Water
           Conditions

    • Authors: Subodh Guragain, Norio Tanaka
      First page: 35
      Abstract: One of the major problems associated with bridge piers is ensuring their safety against local scouring caused by the erosive action of flow. Numerous countermeasures have been developed and tested to solve this problem, among which sacrificial piles are highly recognized due to their high performance, economy, durability, and ease of construction. Several factors affect the performance of sacrificial piles, such as their number, size, degree of submergence, and geometric arrangement parameters. In this study, the performance of a group of linearly arranged cylindrical sacrificial piles in reducing local scour around a circular bridge pier was investigated by varying the number of piles (or sheltering area) and distance between piles and the pier under clear-water conditions. Three values of distance between piles and the pier and three values of sheltering area (or number of piles) were tested. The efficiencies of sacrificial piles in different configurations were presented in terms of the percentage reduction in maximum scour depth at an unprotected pier under the same hydraulic conditions. The results of this experiment show that when linearly arranged sacrificial piles are placed close to the pier (at distance D; D is the pier diameter), an increase in the number of piles (or sheltered area) results in an increased scour depth, and when placed far from the pier (2D and 3D), an increase in the number of piles results in a decrease in scour depth around the pier. In addition, for 40% and 60% sheltering conditions, scour depth increased with an increase in the spacing between piles and the pier, while for 80% sheltering conditions, optimum protection was observed at a distance of 2D. Overall, two piles placed at distance D provided optimum protection with a scour depth reduction of 41.6%, while minimum protection was recorded when the same were placed at a spacing of 3D from the pier (25.5%).
      Citation: Fluids
      PubDate: 2024-01-31
      DOI: 10.3390/fluids9020035
      Issue No: Vol. 9, No. 2 (2024)
       
  • Fluids, Vol. 9, Pages 36: Rheological Characterization of a Thixotropic
           Semisolid Slurry by Means of Numerical Simulations of Squeeze-Flow
           Experiments

    • Authors: Georgios C. Florides, Georgios C. Georgiou, Michael Modigell, Eugenio José Zoqui
      First page: 36
      Abstract: We propose a methodology for the rheological characterization of a semisolid metal slurry using experimental squeeze-flow data. The slurry is modeled as a structural thixotropic viscoplastic material, obeying the regularized Herschel–Bulkley constitutive equation. All rheological parameters are assumed to vary with the structure parameter that is governed by first-order kinetics accounting for the material structure breakdown and build-up. The squeeze flow is simulated using finite elements in a Lagrangian framework. The evolution of the sample height has been studied for wide ranges of the Bingham and Reynolds numbers, the power-law exponent as well as the kinetics parameters of the structure parameter. Systematic comparisons have been carried out with available experimental data on a semisolid aluminum alloy (A356), where the sample is compressed from its top side under a specified strain of 80% at a temperature of 582 °C, while the bottom side remains fixed. Excellent agreement with the experimental data could be achieved provided that at the initial instances (up to 0.01 s) of the experiment, the applied load is much higher than the nominal experimental load and that the yield stress and the power-law exponent vary linearly with the structure parameter. The first assumption implies that a different model, such as an elastoviscoplastic one, needs to be employed during the initial stages of the experiment. As for the second one, the evolution of the sample height can be reproduced allowing the yield stress to vary from 0 (no structure) to a maximum nominal value (full structure) and the power-law exponent from 0.2 to 1.4, i.e., from the shear-thinning to the shear-thickening regime. These variations are consistent with the internal microstructure variation pattern known to be exhibited by semisolid slurries.
      Citation: Fluids
      PubDate: 2024-01-31
      DOI: 10.3390/fluids9020036
      Issue No: Vol. 9, No. 2 (2024)
       
  • Fluids, Vol. 9, Pages 37: Numerical Analysis of Non-Newtonian Fluid
           Effects on the Equilibrium Position of a Suspended Particle and Relative
           Viscosity in Two-Dimensional Flow

    • Authors: Keiya Tomioka, Tomohiro Fukui
      First page: 37
      Abstract: A solvent in suspension often has non-Newtonian properties. To date, in order to determine these properties, many constitutive equations have been suggested. In particular, power-law fluid, which describes both dilatant and pseudoplastic fluids, has been used in many previous studies because of its simplicity. Then, the Herschel–Bulkley model is used, which describes fluid with yield stress. In this study, we considered how a non-Newtonian solvent affected the equilibrium position of a particle and relative viscosity using the regularized lattice Boltzmann method for fluid and a two-way coupling scheme for the particle. We focused on these methods so as to evaluate the non-Newtonian effects of a solvent. The equilibrium position in Bingham fluid was closer to the wall than that in Newtonian or power-law fluid. In contrast, the tendency of relative viscosity in Bingham fluid for each position was similar to that in power-law fluid.
      Citation: Fluids
      PubDate: 2024-02-01
      DOI: 10.3390/fluids9020037
      Issue No: Vol. 9, No. 2 (2024)
       
  • Fluids, Vol. 9, Pages 38: Hydraulic Flushing of Sediment in Reservoirs:
           Best Practices of Numerical Modeling

    • Authors: Yong G. Lai, Jianchun Huang, Blair P. Greimann
      First page: 38
      Abstract: This article provides a comprehensive review and best practices for numerically simulating hydraulic flushing for reservoir sediment management. Three sediment flushing types are discussed: drawdown flushing, pressure flushing, and turbidity current venting. The need for reservoir sediment management and the current practices are reviewed. Different hydraulic drawdown types are described in terms of the basic physical processes involved as well as the empirical/analytical assessment tools that may be used. The primary focus has been on the numerical modeling of various hydraulic flushing options. Three model categories are reviewed: one-dimensional (1D), two-dimensional (2D) depth-averaged or layer-averaged, and three-dimensional (3D) computational fluid dynamics (CFD) models. General guidelines are provided on how to select a proper model given the characteristics of the reservoir and the flushing method, as well as specific guidelines for modeling. Case studies are also presented to illustrate the guidelines.
      Citation: Fluids
      PubDate: 2024-02-01
      DOI: 10.3390/fluids9020038
      Issue No: Vol. 9, No. 2 (2024)
       
  • Fluids, Vol. 9, Pages 39: Experimental Studies on Vortex-Induced Vibration
           of a Piggyback Pipeline

    • Authors: Difei Xiao, Zhiyong Hao, Tongming Zhou, Hongjun Zhu
      First page: 39
      Abstract: Offshore pipelines of different diameters are often seen in piggyback arrangements in close proximity. Under the effects of external flows, the pipelines may experience vibration. Reliable prediction of the vibration amplitudes is important for the design and operation of these structures. In the present study, the effect of the position angle (α) and gap ratio (G/D) of a piggyback pipeline on the amplitude of 1DOF vortex-induced vibration (VIV) was investigated experimentally in a wind tunnel. The diameter ratio d/D of the two cylinders was 0.5. Five position angles, namely, α = 0°, 45°, 90°, 135°, and 180°, and six gap ratios at each angle, G/D = 0, 0.1, 0.2, 0.3, 0.4, 0.5, were tested. It was found that both α and G/D affected the amplitude of vibrations significantly. For all gap ratios, the amplitude of vibrations increased from α = 0° to α = 90° and then decreased to a minimum value around α = 135°. The maximum amplitude occurred around α = 90° when G/D = 0, and the minimum occurred around α = 135°, when G/D = 0.2–0.3. At other position angles, the vibration amplitude was less sensitive to G/D, especially when the latter was between 0.1 and 0.4. These results verified those obtained using numerical methods and are invaluable to engineers when designing offshore piggyback pipelines.
      Citation: Fluids
      PubDate: 2024-02-01
      DOI: 10.3390/fluids9020039
      Issue No: Vol. 9, No. 2 (2024)
       
  • Fluids, Vol. 9, Pages 40: Interpreting Image Patterns for Agricultural
           Sprays Using Statistics and Machine Learning Techniques

    • Authors: Steven Cryer, John Raymond
      First page: 40
      Abstract: The atomization of liquid spray solutions through nozzles is a mechanism for delivering many pesticides to the target. The smallest drop sizes (<150 μm) are known as driftable fines and have a propensity for wind-induced convection. Many agricultural applications include oil-in-water formulations. The experimental metrics obtained from spray images of these formulations include the distance from the nozzle origin to the drop centroid once a drop has formed; the hole location and surface area for holes that form in the liquid sheet (all hole areas approximated as polygons); the angles formed between polygon segments (whose vertices are represented as boundary points); and the ligament dimensions that form from intersecting holes, such as the ligament aspect ratio (R/L), ligament length (L), and ligament radius (width), along with the number of drops a ligament breaks up into. These metrics were used in a principal component regression (PCR) analysis, and the results illustrated that 99% of the variability in the response variable (DT10) was addressed by 10 principal components. Angles formed by the colliding holes, hole distance from the nozzle, drop distance, hole number, ligament number, and drop number were negatively correlated to the atomization driftable fine fraction, while hole area, ligament distance, ligament area, and boundary area were positively correlated. Thus, to decrease/minimize driftable fines, one needs to increase the negatively correlated metrics.
      Citation: Fluids
      PubDate: 2024-02-01
      DOI: 10.3390/fluids9020040
      Issue No: Vol. 9, No. 2 (2024)
       
  • Fluids, Vol. 9, Pages 41: Effect of Dissolved Carbon Dioxide on Cavitation
           in a Circular Orifice

    • Authors: Sina Safaei, Carsten Mehring
      First page: 41
      Abstract: In this work, we investigate the effect of dissolved gas concentration on cavitation inception and cavitation development in a transparent sharp-edged orifice, similar to that previously analyzed by Nurick in the context of liquid injectors. The working liquid is water, and carbon dioxide is employed as a non-condensable dissolved gas. Cavitation inception points are determined for different dissolved gas concentration levels by measuring wall-static pressures just downstream of the orifice contraction and visually observing the onset of a localized (vapor) bubble cloud formation and collapse. Cavitation onset correlates with a plateau in wall-static pressure measurements as a function of a cavitation number. An increase in the amount of dissolved carbon dioxide is found to increase the cavitation number at which the onset of cavitation occurs. The transition from cloud cavitation to extended-sheet or full cavitation along the entire orifice length occurs suddenly and is shifted to higher cavitation numbers with increasing dissolved gas content. Volume flow rate measurements are performed to determine the change in the discharge coefficient with the cavitation number and dissolved gas content for the investigated cases. CFD analyses are carried out based on the cavitation model by Zwart et al. and the model by Yang et al. to account for non-condensable gases. Discharge coefficients obtained from the numerical simulations are in good agreement with experimental values, although they are slightly higher in the cavitating case. The earlier onset of fluid cavitation (i.e., cavitation inception at higher cavitation numbers) with increasing dissolved carbon dioxide content is not predicted using the employed numerical model.
      Citation: Fluids
      PubDate: 2024-02-01
      DOI: 10.3390/fluids9020041
      Issue No: Vol. 9, No. 2 (2024)
       
  • Fluids, Vol. 9, Pages 42: A Comprehensive Evaluation of Turbulence Models
           for Predicting Heat Transfer in Turbulent Channel Flow across Various
           Prandtl Number Regimes

    • Authors: Liyuan Liu, Umair Ahmed, Nilanjan Chakraborty
      First page: 42
      Abstract: Turbulent heat transfer in channel flows is an important area of research due to its simple geometry and diverse industrial applications. Reynolds-Averaged Navier–Stokes (RANS) models are the most-affordable simulation methodology and are often the only viable choice for investigating industrial flows. However, accurate modelling of wall-bounded flows is challenging in RANS, and the assessment of the performance of RANS models for heated turbulent channel flow has not been sufficiently investigated for a wide range of Reynolds and Prandtl numbers. In this study, five RANS models are assessed for their ability to predict heat transfer in channel flows across a wide range of Reynolds and Prandtl numbers (Pr) by comparing the RANS results with respect to the corresponding Direct Numerical Simulation data. The models include three Eddy Viscosity Models (EVMs): standard k−ϵ, low Reynolds number k−ϵLS, and k−ωSST, as well as two Reynolds Stress Models (RSMs): Launder–Reece–Rodi and Speziale–Sarkar–Gatski models. The study analyses the Reynolds number effects on turbulent heat transfer in a channel flow at a Pr of 0.71 for friction Reynolds number values of 180,395,640, and 1020. The results show that all models accurately predict velocity across all Reynolds numbers, but the accuracy of mean temperature prediction drops with increasing Reynolds number for all models, except for the k−ωSST model. The study also analyses the Pr effects on turbulent heat transfer in a channel flow with Pr values between 0.025 and 10.0. An error analysis is performed on the results obtained from different turbulence models, and it is shown that the k−ωSST model has the smallest error for the predictions of the mean temperature and Nusselt number for high-Prandtl-number flows, while the low Reynolds number k−ϵLS model shows the smallest errors for low-Prandtl-number flows at different Reynolds numbers. An analytical solution is utilised to identify Pr effects on forced convection in a channel flow into three different regimes: analytical region, transitional region, and turbulent diffusion-dominated region. These regimes are helpful to discuss the validity of the models in relation to the Pr. The findings of this paper provide insights into the performance of different RANS models for heat transfer predictions in a channel flow.
      Citation: Fluids
      PubDate: 2024-02-03
      DOI: 10.3390/fluids9020042
      Issue No: Vol. 9, No. 2 (2024)
       
  • Fluids, Vol. 9, Pages 43: Vortex-Breakdown Efficiency of Planar Regular
           Grid Structures—Towards the Development of Design Guidelines

    • Authors: Julien Sirois, Marlène Sanjosé, Fabian Sanchez, Vladimir Brailovski
      First page: 43
      Abstract: The work presented here aims to provide design guidelines to create vortex-damping structures. A design of experiment was developed to investigate the individual and combined effects of the geometrical properties of planar regular grid structures, i.e., the wire diameter, the porosity, and the inter-grid spacing, on their vortex-breakdown performance. The simulations were carried out using a commercial unsteady RANS solver. The model relies on the Von Karman street effect to generate vortices in a pipe which are convected downstream, where they interact with an array of grids. The vortex-breakdown efficiency is characterized by the pressure drop, the residual turbulent kinetic energy, the flow homogeneity, and the size of the transmitted vortices. The wire diameter is shown to be an important design lever as it affects the level of distortion of the transmitted vortices. Increasing the number of grids augments the pressure loss, but their contribution to vortex breakdown is otherwise limited when the wire diameter is small. The influence of grid spacing strongly depends on the wire diameter and grid alignment. For instance, minimizing this gap reduces the pressure drop for the inline configurations, but increases the pressure drop for the offset configurations.
      Citation: Fluids
      PubDate: 2024-02-08
      DOI: 10.3390/fluids9020043
      Issue No: Vol. 9, No. 2 (2024)
       
  • Fluids, Vol. 9, Pages 44: Comparative Analysis of Simulation Methodologies
           for Spindle Pumps

    • Authors: Pasquale Borriello, Emma Frosina, Pierpaolo Lucchesi, Adolfo Senatore
      First page: 44
      Abstract: This research conducts a comprehensive comparative analysis of simulation methodologies for spindle pumps, with a specific focus on steady-state CFD, transient-CFD, and lumped-parameter approaches. Spindle pumps, renowned for their reliability, efficiency, and low noise emission, play a pivotal role in Thermal Management for Battery Electric Vehicles, aligning with the automotive industry’s commitment to reducing pollutants and CO2 emissions. The study is motivated by the critical need to curtail energy consumption during on-the-road operations, particularly as the automotive industry strives for enhanced efficiency. While centrifugal pumps are commonly employed for such applications, their efficiency is highly contingent on rotational speed, leading to energy wastage in real-world scenarios despite high efficiency at the design point. Consequently, the adoption of precisely designed spindle pumps for thermal management systems emerges as a viable solution to meet evolving industry needs. Recognizing the profound impact of simulation tools on the design and optimization phases for pump manufacturers, this research emphasizes the significance of fast and accurate simulation tools. Transient-CFD emerges as a powerful Tool, enabling real-time monitoring of various performance indicators, while steady-CFD, with minimal simplifications, adeptly captures pressure distribution and machine leakages. Lumped-parameter approaches, though requiring effort in simulation setup and simplifying input geometry, offer rapid computational times and comprehensive predictions, including leakages, Torque, cavitation, and pressure ripple. Breaking new ground, this paper presents, for the first time in the literature, accurate simulation models for the same reference machine using the aforementioned methodologies. The results were rigorously validated against experiments spanning a wide range of pump speeds and pressure drops. The discussion encompasses predicted flow, Torque, cavitation, and pressure ripple, offering valuable insights into the strengths and limitations of each methodology.
      Citation: Fluids
      PubDate: 2024-02-09
      DOI: 10.3390/fluids9020044
      Issue No: Vol. 9, No. 2 (2024)
       
  • Fluids, Vol. 9, Pages 45: CFD Analysis of Ultra-High-Performance Concrete
           Rheological Tests

    • Authors: Tomáš Jirout, Adam Krupica, Alexandr Kolomijec
      First page: 45
      Abstract: This study connects and compares the results from two different rheological measurement techniques, namely, the slump test and rotational rheometry, on UHPC (Ultra-High-Performance Concrete) through the use of commercially available numerical simulation software ANSYS Fluent 2022 R2. The workability and resulting mechanical properties of the UHPC (a material used in construction) are highly dependent on its rheology and, hence, also on the composition and level of homogeneity of the assessed mixture. It is generally understood that the most suitable rheological model for concrete mixtures is the Hershel–Bulkley model. However, obtaining reliable rheological data is complicated as the wide-gap rotational rheometers developed for concrete show bias in their measurements even on precise laboratory equipment, while common industrial tests, such as the slump test, do not produce the usual shear rate–shear stress relation and, hence, do not allow for more complex analysis. Recently, a new methodology for the rheological measurement of non-Newtonian fluids that utilises a simple power input–rotation speed measurement was published. However, in this study, only model liquids were evaluated, and the method was not validated for more complex fluids such as pastes. Therefore, it was the goal of this study to show this method’s suitability for fine pastes through a comparison with the slump test, using numerical simulation.
      Citation: Fluids
      PubDate: 2024-02-11
      DOI: 10.3390/fluids9020045
      Issue No: Vol. 9, No. 2 (2024)
       
  • Fluids, Vol. 9, Pages 46: The Statistical Mechanics of Ideal
           Magnetohydrodynamic Turbulence and a Solution of the Dynamo Problem

    • Authors: John V. Shebalin
      First page: 46
      Abstract: We review and extend the theory of ideal, homogeneous, incompressible, magnetohydrodynamic (MHD) turbulence. The theory contains a solution to the ‘dynamo problem’, i.e., the problem of determining how a planetary or stellar body produces a global dipole magnetic field. We extend the theory to the case of ideal MHD turbulence with a mean magnetic field that is alignedwith a rotation axis. The existing theory is also extended by developing the thermodynamics of ideal MHD turbulence based on entropy. A mathematical model is created by Fourier transforming the MHD equations and dynamical variables, resulting in a dynamical system consisting of the independent Fourier coefficients of the velocity and magnetic fields. This dynamical system has a large but finite-dimensional phase space in which the phase flow is divergenceless in the ideal case. There may be several constants of the motion, in addition to energy, which depend on the presence, or lack thereof, of a mean magnetic field or system rotation or both imposed on the magnetofluid; this leads to five different cases of MHD turbulence that must be considered. The constants of the motion (ideal invariants)—the most important being energy and magnetic helicity—are used to construct canonical probability densities and partition functions that enable ensemble predictions to be made.These predictions are compared with time averages from numerical simulations to test whether or not the system is ergodic. In the cases most pertinent to planets and stars, nonergodicity is observed at the largest length-scales and occurs when the components of the dipole field become quasi-stationary and dipole energy is directly proportional to magnetic helicity. This nonergodicity is evident in the thermodynamics, while dipole alignment with a rotation axis may be seen as the result of dynamical symmetry breaking, i.e., ‘broken ergodicity’. The relevance of ideal theoretical results to real (forced, dissipative) MHD turbulence is shown through numerical simulation. Again, an important result is a statistical solution of the ‘dynamo problem’.
      Citation: Fluids
      PubDate: 2024-02-12
      DOI: 10.3390/fluids9020046
      Issue No: Vol. 9, No. 2 (2024)
       
  • Fluids, Vol. 9, Pages 47: Distinctions of the Emergence of Convective
           Flows at the “Diffusion–Convections” Boundary in
           Isothermal Ternary Gas Mixtures with Carbon Dioxide

    • Authors: Vladimir Kossov, Dauren Zhakebayev, Olga Fedorenko, Ainur Zhumali
      First page: 47
      Abstract: This study discusses the influence of the composition of a ternary gas mixture on the possibility of occurrence of convective instability under isothermal conditions due to the difference in the diffusion abilities of the components. A numerical study was carried out to study the change in “diffusion–concentration gravitational convection” modes in an isothermal three-component gas mixture He + CO2 − N2. The mixing process in the system under study was modeled at different initial carbon dioxide contents. To carry out a numerical experiment, a mathematical algorithm based on the D2Q9 model of lattice Boltzmann equations was used for modeling the flow of gases. We show that the model presented in the paper allows one to study the occurrence of convective structures at different heavy component contents (carbon dioxide). It has been established that in the system under study, the instability of the mechanical equilibrium occurs when the content of carbon dioxide in the mixture is more than 0.3 mole fractions. The characteristic times for the onset of convective instability and the subsequent creation of structural formations, the values of which depend on the initial content of carbon dioxide in the mixture, have been determined. Distributions of concentration, pressure and kinetic energy that allow one to specify the types of mixing and explain the occurrence of convection for a situation where, at the initial moment of time, the density of the gas mixture in the upper part of the diffusion channel is less than in the lower one, were obtained.
      Citation: Fluids
      PubDate: 2024-02-12
      DOI: 10.3390/fluids9020047
      Issue No: Vol. 9, No. 2 (2024)
       
  • Fluids, Vol. 9, Pages 48: Effect of Droplet Viscosity Ratio and Surfactant
           Adsorption on the Coalescence of Droplets with Interfacial Viscosity

    • Authors: Natasha Singh, Vivek Narsimhan
      First page: 48
      Abstract: Surface rheology becomes important for droplets with adsorbed proteins, solid particulates, lipids, or polymers, and understanding how surface rheology alters basic droplet processes like coalescence provides insight into the processing of dispersions in industrial and biological systems. In this work, we model the approach of two equal-size deformable droplets under an axisymmetric, biaxial extensional flow in the Stokes flow limit. We explore how the viscosity contrast between the drop and suspending fluid alters the film drainage behaviour when interfacial viscosity is present. For a clean droplet at a fixed capillary number, the drainage time is observed to be independent of the viscosity ratio (λ) for λ≤O(1), while the drainage increases linearly with the viscosity ratio for λ≥O(1). Surface viscosity increases the drainage time by causing the thin film between the droplets to flatten and widen, and shifts the viscosity ratio at which the aforementioned scaling behaviour changes to larger values. The drainage time is increased more significantly at lower viscosity ratio values than higher values. In the second half of the paper, we examine how surface viscosity alters film drainage when the surfactant can be soluble. We examine the kinetically controlled adsorption/desorption limit. We find that surfactant solubility abolishes surface tension gradients and increases the prominence of surface viscosity effects, the effects of which are quantified for Boussinesq numbers Bq∼O(0.1).
      Citation: Fluids
      PubDate: 2024-02-13
      DOI: 10.3390/fluids9020048
      Issue No: Vol. 9, No. 2 (2024)
       
  • Fluids, Vol. 9, Pages 49: Bursting Sand Balloons

    • Authors: Gustavo Gómez, Francisco José Higuera, Florencio Sánchez-Silva, Abraham Medina
      First page: 49
      Abstract: Using linear elasticity theory, we describe the mechanical response of dry non-cohesive granular masses of Ottawa sand contained by spherical rubber balloons subject to sudden bursting in the earliest instants of the event. Due to the compression imposed by the balloon, the rupture produces a fast radial expansion of the sand front that depends on the initial radius R0, the initial pressure p originated by the balloon, and the effective modulus of compression Ke. The hydrostatic compression approximation allows for the theoretical study of this problem. We found a linear decompression wave that travels into the sand and that induces a radial expansion of the granular front in the opposite direction with similar behavior to the wave but with a slightly lower speed.
      Citation: Fluids
      PubDate: 2024-02-14
      DOI: 10.3390/fluids9020049
      Issue No: Vol. 9, No. 2 (2024)
       
  • Fluids, Vol. 9, Pages 50: Hemodynamic Insights into Abdominal Aortic
           Aneurysms: Bridging the Knowledge Gap for Improved Patient Care

    • Authors: Suvash C. Saha, Isabella Francis, Goutam Saha, Xinlei Huang, Md. Mamun Molla
      First page: 50
      Abstract: Background: Abdominal aortic aneurysms (AAAs) present a formidable public health concern due to their propensity for localized, anomalous expansion of the abdominal aorta. These insidious dilations, often in their early stages, mask the life-threatening potential for rupture, which carries a grave prognosis. Understanding the hemodynamic intricacies governing AAAs is paramount for predicting aneurysmal growth and the imminent risk of rupture. Objective: Our extensive investigation delves into this complex hemodynamic environment intrinsic to AAAs, utilizing comprehensive numerical analyses of the physiological pulsatile blood flow and realistic boundary conditions to explore the multifaceted dynamics influencing aneurysm rupture risk. Our study introduces novel elements by integrating these parameters into the overall context of aneurysm pathophysiology, thus advancing our understanding of the intricate mechanics governing their evolution and rupture. Methods: Conservation of mass and momentum equations are used to model the blood flow in an AAAs, and these equations are solved using a finite volume-based ANSYS Fluent solver. Resistance pressure outlets following a three-element Windkessel model were imposed at each outlet to accurately model the blood flow and the AAAs’ shear stress. Results: Our results uncover elevated blood flow velocities within an aneurysm, suggesting an augmented risk of future rupture due to increased stress in the aneurysm wall. During the systole phase, high wall shear stress (WSS) was observed, typically associated with a lower risk of rupture, while a low oscillatory shear index (OSI) was noted, correlating with a decreased risk of aneurysm expansion. Conversely, during the diastole phase, low WSS and a high OSI were identified, potentially weakening the aneurysm wall, thereby promoting expansion and rupture. Conclusion: Our study underscores the indispensable role of computational fluid dynamic (CFD) techniques in the diagnostic, therapeutic, and monitoring realms of AAAs. This body of research significantly advances our understanding of aneurysm pathophysiology, thus offering pivotal insights into the intricate mechanics underpinning their progression and rupture, informing clinical interventions and enhancing patient care.
      Citation: Fluids
      PubDate: 2024-02-15
      DOI: 10.3390/fluids9020050
      Issue No: Vol. 9, No. 2 (2024)
       
  • Fluids, Vol. 9, Pages 51: Dynamic Mesh Simulations in OpenFOAM: A Hybrid
           Eulerian–Lagrangian Approach

    • Authors: Rention Pasolari, Carlos Simão Ferreira, Alexander van van Zuijlen, Carlos Fernando Baptista
      First page: 51
      Abstract: The past few decades have witnessed a growing popularity in Eulerian–Lagrangian solvers due to their significant potential for simulating aerodynamic flows, particularly in cases involving strong body–vortex interactions. In this hybrid approach, the two component solvers are mutually coupled in a two-way fashion. Initially, the Lagrangian solver can supply boundary conditions to the Eulerian solver, while the Eulerian solver functions as a corrector for the Lagrangian solution in regions where the latter cannot achieve high accuracy. To utilize such tools effectively, it is vital for them to be capable of handling dynamic mesh movements. This study builds upon the previous research conducted by our team and extends the capabilities of the hybrid solver to handle dynamic meshes. While OpenFOAM, the Eulerian component of this hybrid code, incorporates built-in dynamic mesh properties, certain modifications are necessary to ensure its compatibility with the Lagrangian solver. More specifically, the evolution algorithm of the pimpleFOAM solver needs to be divided into two discrete steps: first, updating the mesh, and later, evolving the solution. This division enables a proper coupling between pimpleFOAM and the Lagrangian solver as an intermediate step. Therefore, the primary objective of this specific paper is to adapt the OpenFOAM solver to meet the demands of the hybrid solver and subsequently validate that the hybrid solver can effectively address dynamic mesh challenges using this approach. This approach introduces a pioneering method for conducting dynamic mesh simulations within the OpenFOAM framework, showcasing its potential for broader applications. To validate the approach, various test cases involving dynamic mesh movements are employed. Specifically, all these cases employ the Lamb–Oseen diffusing vortex, but each case incorporates different types of mesh movements, including translational, rotational, oscillational, and combinations thereof. The results from these cases demonstrate the effectiveness of the proposed OpenFOAM algorithm, with the maximum relative errors —when compared to the analytical solution across all presented cases—capped at 2.0% for the worst-case scenario. This affirms the algorithm’s capability to successfully handle dynamic mesh simulations with the proposed solver.
      Citation: Fluids
      PubDate: 2024-02-16
      DOI: 10.3390/fluids9020051
      Issue No: Vol. 9, No. 2 (2024)
       
  • Fluids, Vol. 9, Pages 14: Degradation Identification of an EHA Piston Pump
           by Analysis of Load-Holding States

    • Authors: Yannick Duensing, Amos Merkel, Katharina Schmitz
      First page: 14
      Abstract: In pursuit of advancing the development of more electric aircraft, the present research explores the forefront capabilities of electro-hydrostatic actuators (EHAs) as potential replacements for conventional hydraulic flight control systems. EHAs are currently used primarily as backup options due to their limited durability. As of now, the high dynamic axial piston pump is the main cause of the limited longevity of the EHA, due to strong tribological wear. The primary objective of this investigation is the identification of parameters and pump behavior to determine the current wear of the pump, as well as providing valuable insights into run-ins, temperature dependencies, and wear-related efficiency losses for future pump improvements. In the scope of this paper, the design of EHAs is explained in detail and the impact of challenging working conditions on the health status of the pump by comprehensive analysis of load-holding modes is examined. The experimental data for analysis is conducted on a longevity test bench with test profiles specifically designed to simulate real-world operational scenarios.
      Citation: Fluids
      PubDate: 2024-01-02
      DOI: 10.3390/fluids9010014
      Issue No: Vol. 9, No. 1 (2024)
       
  • Fluids, Vol. 9, Pages 15: From Navier to Stokes: Commemorating the
           Bicentenary of Navier’s Equation on the Lay of Fluid Motion

    • Authors: Aldo Tamburrino
      First page: 15
      Abstract: The article presents a summarised history of the equations governing fluid motion, known as the Navier–Stokes equations. It starts with the work of Castelli, who established the continuity equation in 1628. The determination of fluid flow resistance was a topic that involved the brightest minds of the 17th and 18th centuries. Navier’s contribution consisted of the incorporation of molecular attraction effects into Euler’s equation, giving rise to an additional term associated with resistance. However, his analysis was not the only one. This continued until 1850, when Stokes firmly established the boundary conditions that must be applied to the differential equations of motion, specifically stating the non-slip condition of the fluid in contact with a solid surface. With this article, the author wants to commemorate the bicentennial of the publication of “Sur les Lois du Mouvement des Fluides” by Navier in the Mémoires de l’Académie Royale des Sciences de l’Institut de France.
      Citation: Fluids
      PubDate: 2024-01-06
      DOI: 10.3390/fluids9010015
      Issue No: Vol. 9, No. 1 (2024)
       
  • Fluids, Vol. 9, Pages 16: A GPU-Accelerated Modern Fortran Version of the
           ECHO Code for Relativistic Magnetohydrodynamics

    • Authors: Luca Del Zanna, Simone Landi, Lorenzo Serafini, Matteo Bugli, Emanuele Papini
      First page: 16
      Abstract: The numerical study of relativistic magnetohydrodynamics (MHD) plays a crucial role in high-energy astrophysics but unfortunately is computationally demanding, given the complex physics involved (high Lorentz factor flows, extreme magnetization, and curved spacetimes near compact objects) and the large variety of spatial scales needed to resolve turbulent motions. A great benefit comes from the porting of existing codes running on standard processors to GPU-based platforms. However, this usually requires a drastic rewriting of the original code, the use of specific languages like CUDA, and a complex analysis of data management and optimization of parallel processes. Here, we describe the porting of the ECHO code for special and general relativistic MHD to accelerated devices, simply based on native Fortran language built-in constructs, especially do concurrent loops, few OpenACC directives, and straightforward data management provided by the Unified Memory option of NVIDIA compilers. Thanks to these very minor modifications to the original code, the new version of ECHO runs at least 16 times faster on GPU platforms as compared to CPU-based ones. The chosen benchmark is the 3D propagation of a relativistic MHD Alfvén wave, for which strong and weak scaling tests performed on the LEONARDO pre-exascale supercomputer at CINECA are provided (using up to 256 nodes corresponding to 1024 GPUs, and over 14 billion cells). Finally, an example of high-resolution relativistic MHD Alfvénic turbulence simulation is shown, demonstrating the potential for astrophysical plasmas of the new GPU-based version of ECHO.
      Citation: Fluids
      PubDate: 2024-01-06
      DOI: 10.3390/fluids9010016
      Issue No: Vol. 9, No. 1 (2024)
       
  • Fluids, Vol. 9, Pages 17: Wind Velocity and Forced Heat Transfer Model for
           Photovoltaic Module

    • Authors: Reza Hassanian, Nashmin Yeganeh, Morris Riedel
      First page: 17
      Abstract: This study proposes a computational model to define the wind velocity of the environment on the photovoltaic (PV) module via heat transfer concepts. The effect of the wind velocity and PV module is mostly considered a cooling effect. However, cooling and controlling the PV module temperature leads to the capability to optimize the PV module efficiency. The present study applied a nominal operating cell temperature (NOCT) condition of the PV module as a reference condition to determine the wind velocity and PV module temperature. The obtained model has been examined in contrast to the experimental heat transfer equation and outdoor PV module performance. The results display a remarkable matching of the model with experiments. The model’s novelty defines the PV module temperature in relation to the wind speed, PV module size, and various ambient temperatures that were not included in previous studies. The suggested model could be used in PV module test specification and provide analytical evaluation.
      Citation: Fluids
      PubDate: 2024-01-07
      DOI: 10.3390/fluids9010017
      Issue No: Vol. 9, No. 1 (2024)
       
  • Fluids, Vol. 9, Pages 18: A Spectral/hp-Based Stabilized Solver with
           Emphasis on the Euler Equations

    • Authors: Rakesh Ranjan, Lucia Catabriga, Guillermo Araya
      First page: 18
      Abstract: The solution of compressible flow equations is of interest with many aerospace engineering applications. Past literature has focused primarily on the solution of Computational Fluid Dynamics (CFD) problems with low-order finite element and finite volume methods. High-order methods are more the norm nowadays, in both a finite element and a finite volume setting. In this paper, inviscid compressible flow of an ideal gas is solved with high-order spectral/hp stabilized formulations using uniform high-order spectral element methods. The Euler equations are solved with high-order spectral element methods. Traditional definitions of stabilization parameters used in conjunction with traditional low-order bilinear Lagrange-based polynomials provide diffused results when applied to the high-order context. Thus, a revision of the definitions of the stabilization parameters was needed in a high-order spectral/hp framework. We introduce revised stabilization parameters, τsupg, with low-order finite element solutions. We also reexamine two standard definitions of the shock-capturing parameter, δ: the first is described with entropy variables, and the other is the YZβ parameter. We focus on applications with the above introduced stabilization parameters and analyze an array of problems in the high-speed flow regime. We demonstrate spectral convergence for the Kovasznay flow problem in both L1 and L2 norms. We numerically validate the revised definitions of the stabilization parameter with Sod’s shock and the oblique shock problems and compare the solutions with the exact solutions available in the literature. The high-order formulation is further extended to solve shock reflection and two-dimensional explosion problems. Following, we solve flow past a two-dimensional step at a Mach number of 3.0 and numerically validate the shock standoff distance with results obtained from NASA Overflow 2.2 code. Compressible flow computations with high-order spectral methods are found to perform satisfactorily for this supersonic inflow problem configuration. We extend the formulation to solve the implosion problem. Furthermore, we test the stabilization parameters on a complex flow configuration of AS-202 capsule analyzing the flight envelope. The proposed stabilization parameters have shown robustness, providing excellent results for both simple and complex geometries.
      Citation: Fluids
      PubDate: 2024-01-08
      DOI: 10.3390/fluids9010018
      Issue No: Vol. 9, No. 1 (2024)
       
  • Fluids, Vol. 9, Pages 19: Quantitative Color Schlieren for an H2–O2
           Exhaust Jet Developing in Air

    • Authors: Emilia-Georgiana Prisăcariu, Tudor Prisecaru
      First page: 19
      Abstract: Throughout many decades, the Schlieren visualization method has been mainly used as means to visualize transparent flows in a qualitative manner. The images recorded provide data regarding the existence of the flow, or illustrate predicted flow geometries and details. The colored Schlieren method has been developed in the late 1890s and has always had the intent to provide quantitative data rather than qualitative pictures of the studied phenomena. This paper centers on applying a quantitative color Schlieren method to help determine the gasodynamic parameters of an H2–O2 exhaust jet, developing in air. A comparison between the parameters obtained through calibrating the color filter for the Schlieren method and the results from a CFD simulation is performed to assess the range of the CS (color Schlieren) measurement. This paper’s findings address the issues of calibrated color filter Schlieren encounter during its implementation and discusses possible errors appearing when the method is applied to a 3D flow. While the qualitative Schlieren images are still impressive to observe, the quantitative Schlieren presents challenges and a low measurement accuracy (75%) when applied to 3D flows and compared to 2D cases found in the literature (97–98%).
      Citation: Fluids
      PubDate: 2024-01-08
      DOI: 10.3390/fluids9010019
      Issue No: Vol. 9, No. 1 (2024)
       
  • Fluids, Vol. 9, Pages 20: Application of Machine Learning Algorithms in
           Predicting Rheological Behavior of BN-diamond/Thermal Oil Hybrid
           Nanofluids

    • Authors: Abulhassan Ali, Nawal Noshad, Abhishek Kumar, Suhaib Umer Ilyas, Patrick E. Phelan, Mustafa Alsaady, Rizwan Nasir, Yuying Yan
      First page: 20
      Abstract: The use of nanofluids in heat transfer applications has significantly increased in recent times due to their enhanced thermal properties. It is therefore important to investigate the flow behavior and, thus, the rheology of different nanosuspensions to improve heat transfer performance. In this study, the viscosity of a BN-diamond/thermal oil hybrid nanofluid is predicted using four machine learning (ML) algorithms, i.e., random forest (RF), gradient boosting regression (GBR), Gaussian regression (GR) and artificial neural network (ANN), as a function of temperature (25–65 °C), particle concentration (0.2–0.6 wt.%), and shear rate (1–2000 s−1). Six different error matrices were employed to evaluate the performance of these models by providing a comparative analysis. The data were randomly divided into training and testing data. The algorithms were optimized for better prediction of 700 experimental data points. While all ML algorithms produced R2 values greater than 0.99, the most accurate predictions, with minimum error, were obtained by GBR. This study indicates that ML algorithms are highly accurate and reliable for the rheological predictions of nanofluids.
      Citation: Fluids
      PubDate: 2024-01-09
      DOI: 10.3390/fluids9010020
      Issue No: Vol. 9, No. 1 (2024)
       
  • Fluids, Vol. 9, Pages 21: Deeper Flow Behavior Explanation of Temperature
           Effects on the Fluid Dynamic inside a Tundish

    • Authors: Enif Gutiérrez, Saul Garcia-Hernandez, Rodolfo Morales Davila, Jose de Jesus Barreto
      First page: 21
      Abstract: The continuous casting tundish is non-isothermal due to heat losses and temperature variation from the inlet stream, which generate relevant convection forces. This condition is commonly avoided through qualitative fluid dynamic analysis only. This work searches to establish the conditions for which non-isothermal simulations are mandatory or for which isothermal simulations are enough to accurately describe the fluid dynamics inside the tundish by quantifying the buoyant and inertial forces. The mathematical model, simulated by CFD software, considers the Navier-Stokes equations, the realizable k-ε model for solving the turbulence, and the Lagrangian discrete phase to track the inclusion trajectories. The results show that temperature does not significantly impact the volume fraction percentages or the mean residence time results; nevertheless, bigger velocity magnitudes under non-isothermal conditions than in isothermal conditions and noticeable changes in the fluid dynamics between isothermal and non-isothermal cases in all the zones where buoyancy forces dominate over inertial forces were observed. Because of the results, it is concluded that isothermal simulations can accurately describe the flow behavior in tundishes when the flow control devices control the fluid dynamics, but simulations without control devices or with a weak fluid dynamic dependence on the control devices require non-isothermal simulations.
      Citation: Fluids
      PubDate: 2024-01-10
      DOI: 10.3390/fluids9010021
      Issue No: Vol. 9, No. 1 (2024)
       
  • Fluids, Vol. 9, Pages 22: Continuous Eddy Simulation vs.
           Resolution-Imposing Simulation Methods for Turbulent Flows

    • Authors: Adeyemi Fagbade, Stefan Heinz
      First page: 22
      Abstract: The usual concept of simulation methods for turbulent flows is to impose a certain (partial) flow resolution. This concept becomes problematic away from limit regimes of no or an almost complete flow resolution: discrepancies between the imposed and actual flow resolution may imply an unreliable model behavior and high computational cost to compensate for simulation deficiencies. An exact mathematical approach based on variational analysis provides a solution to these problems. Minimal error continuous eddy simulation (CES) designed in this way enables simulations in which the model actively responds to variations in flow resolution by increasing or decreasing its contribution to the simulation as required. This paper presents the first application of CES methods to a moderately complex, relatively high Reynolds number turbulent flow simulation: the NASA wall-mounted hump flow. It is shown that CES performs equally well or better than almost resolving simulation methods at a little fraction of computational cost. Significant computational cost and performance advantages are reported in comparison to popular partially resolving simulation methods including detached eddy simulation and wall-modeled large eddy simulation. Characteristic features of the asymptotic flow structure are identified on the basis of CES simulations.
      Citation: Fluids
      PubDate: 2024-01-10
      DOI: 10.3390/fluids9010022
      Issue No: Vol. 9, No. 1 (2024)
       
  • Fluids, Vol. 9, Pages 23: Calibration of Thixotropic and Viscoelastic
           Shear-Thinning Fluids Using Pipe Rheometer Measurements

    • Authors: Eric Cayeux
      First page: 23
      Abstract: Some non-Newtonian fluids have time-dependent rheological properties like a shear stress that depends on the shear history or a stress overshoot that is a function of the resting time, when fluid movement is started. The rheological properties of such complex fluids may not stay constant while they are used in an industrial process, and it is therefore desirable to measure these properties frequently and with a simple and robust device like a pipe rheometer. This paper investigated how the time-dependent rheological properties of a thixotropic and viscoelastic shear-thinning fluid can be extracted from differential pressure measurements obtained at different flowrates along a circular pipe section. The method consists in modeling the flow of a thixotropic version of a Quemada fluid and solving the inverse problem in order to find the model parameters using the measurements made in steady-state conditions. Also, a Maxwell linear viscoelastic model was used to reproduce the stress overshoot observed when starting circulation after a resting period. The pipe rheometer was designed to have the proper features necessary to exhibit the thixotropic and viscoelastic effects that were needed to calibrate the rheological model parameters. The accuracy of rheological measurements depends on understanding the effects that can influence the observations and on a proper design that takes advantage of these side effects instead of attempting to eliminate them.
      Citation: Fluids
      PubDate: 2024-01-10
      DOI: 10.3390/fluids9010023
      Issue No: Vol. 9, No. 1 (2024)
       
  • Fluids, Vol. 9, Pages 24: Parametrization Effects of the Non-Linear
           Unsteady Vortex Method with Vortex Particle Method for Small Rotor
           Aerodynamics

    • Authors: Vincent Proulx-Cabana, Guilhem Michon, Eric Laurendeau
      First page: 24
      Abstract: The aim of this article is to investigate the parameter sensitivity of the (Non-Linear) Unsteady Vortex Lattice Method-Vortex Particle Method [(NL-)UVLM-VPM] with Particle Strength Exchange-Large Eddy Simulations (PSE-LES) method on a lower Reynolds number rotor. The previous work detailed the method, but introduced parameters whose influence were not investigated. Most importantly, the Vreman model coefficient was chosen arbitrarily and was not suitable to ensure stability for this lower Reynolds number rotor simulation. In addition, the previous work presented a consistency study where geometry and time discretization were refined simultaneously. The present article starts with a comparative literature review of potential methods used to solve the aerodynamics of an isolated hovering rotor. This review highlights the differences in modeling, discretizations, sensitivity analysis, validation cases, and the results chosen by the different studies. Then, a transparent and thorough parametric study of the method is presented alongside discussions of the observed results and their physical interpretation regarding the flow. The sensitivity analysis is performed for the three free parameters of UVLM, namely Vatistas core size, the geometry and the temporal discretizations, and then for the three additional parameters introduced by UVLM-VPM, which are the Vreman model coefficient, the particle spacing, and the conversion time. The effect of different databases in the non-linear coupling is also shown. The method is shown to be consistent with both geometry and temporal refinements. It is also consistent with the expected behavior of the different parameters change, including the numerical stability that depends on the strength of the LES diffusion controlled by the Vreman model coefficient. The effect of discretization refinement presented here not only shows the integrated coefficients where different errors can cancel each other, but also looks at their convergence and where relevant, the distributed loads and tip singularity position. Finally, the aerodynamics results of the method are compared for different databases and with higher fidelity Unsteady Reynolds Averaged Navier–Stokes (URANS) 3D results on a lower Reynolds number rotor.
      Citation: Fluids
      PubDate: 2024-01-15
      DOI: 10.3390/fluids9010024
      Issue No: Vol. 9, No. 1 (2024)
       
  • Fluids, Vol. 9, Pages 25: The Asymptotic Structure of Canonical
           Wall-Bounded Turbulent Flows

    • Authors: Stefan Heinz
      First page: 25
      Abstract: Our ability to reliably and efficiently predict complex high-Reynolds-number (Re) turbulent flows is essential for dealing with a large variety of problems of practical relevance. However, experiments as well as computational methods such as direct numerical simulation (DNS) and large eddy simulation (LES) face serious questions regarding their applicability to high Re turbulent flows. The most promising option to create reliable guidelines for experimental and computational studies is the use of analytical conclusions. An essential criterion for the reliability of such analytical conclusions is the inclusion of a physically plausible explanation of the asymptotic turbulence regime at infinite Re in consistency with observed physical requirements. Corresponding analytical results are reported here for three canonical wall-bounded turbulent flows: channel flow, pipe flow, and the zero-pressure gradient turbulent boundary layer. The asymptotic structure of the mean velocity and characteristic turbulence velocity, length, and time scales is analytically determined. In outer scaling, a stable asymptotic mean velocity distribution is found corresponding to a linear probability density function of mean velocities along the wall-normal direction, which is modified through wake effects. Turbulence tends to decay in this regime. In inner scaling, the mean velocity is governed by a universal log-law. Turbulence does survive in an infinitesimally thin layer very close to the wall.
      Citation: Fluids
      PubDate: 2024-01-17
      DOI: 10.3390/fluids9010025
      Issue No: Vol. 9, No. 1 (2024)
       
  • Fluids, Vol. 9, Pages 26: Control of Aerodynamic Characteristics of Thick
           Airfoils at Low Reynolds Numbers Using Methods of Boundary Layer Control

    • Authors: Pavel Bulat, Pavel Chernyshov, Nikolay Prodan, Konstantin Volkov
      First page: 26
      Abstract: The article explores flow behavior around thick airfoils at low Reynolds numbers and the potential application of energy methods to manipulate the flow field for increased lift and reduced drag. The study relies on a set of propulsion airfoils calculated using a combined approach of solving the inverse problem of aerodynamics and applying stochastic global optimization methods. The calculations consider the transition from laminar to turbulent flow regimes, which significantly affects lift and airfoil drag. The suitability of different turbulence models for airfoil modeling in low Reynolds numbers is discussed, and numerical simulation results determine the lift coefficient dependence on angle of attack and the optimal air flow rate taken from the airfoil surface for each angle of attack. The accuracy of different turbulence models is analyzed by comparing numerical simulation results to physical experiment data.
      Citation: Fluids
      PubDate: 2024-01-17
      DOI: 10.3390/fluids9010026
      Issue No: Vol. 9, No. 1 (2024)
       
  • Fluids, Vol. 9, Pages 27: A Parametric 3D Model of Human Airways for
           Particle Drug Delivery and Deposition

    • Authors: Leonardo Geronzi, Benigno Marco Fanni, Bart De Jong, Gerben Roest, Sasa Kenjeres, Simona Celi, Marco Evangelos Biancolini
      First page: 27
      Abstract: The treatment for asthma and chronic obstructive pulmonary disease relies on forced inhalation of drug particles. Their distribution is essential for maximizing the outcomes. Patient-specific computational fluid dynamics (CFD) simulations can be used to optimize these therapies. In this regard, this study focuses on creating a parametric model of the human respiratory tract from which synthetic anatomies for particle deposition analysis through CFD simulation could be derived. A baseline geometry up to the fourth generation of bronchioles was extracted from a CT dataset. Radial basis function (RBF) mesh morphing acting on a dedicated tree structure was used to modify this baseline mesh, extracting 1000 synthetic anatomies. A total of 26 geometrical parameters affecting branch lengths, angles, and diameters were controlled. Morphed models underwent CFD simulations to analyze airflow and particle dynamics. Mesh morphing was crucial in generating high-quality computational grids, with 96% of the synthetic database being immediately suitable for accurate CFD simulations. Variations in wall shear stress, particle accretion rate, and turbulent kinetic energy across different anatomies highlighted the impact of the anatomical shape on drug delivery and deposition. The study successfully demonstrates the potential of tree-structure-based RBF mesh morphing in generating parametric airways for drug delivery studies.
      Citation: Fluids
      PubDate: 2024-01-18
      DOI: 10.3390/fluids9010027
      Issue No: Vol. 9, No. 1 (2024)
       
  • Fluids, Vol. 9, Pages 28: Combined Impact of the Lewis Number and Thermal
           Expansion on Laminar Flame Flashback in Tubes

    • Authors: Kai Huang, Louis Benteux, Wenhu Han, Damir M. Valiev
      First page: 28
      Abstract: The understanding of the boundary layer flame flashback (BLF) has considerably improved in recent decades, driven by the increasing focus on clean energy and the need to address the operational issues associated with flashback. This study investigates the influence of the Lewis number (Le) on symmetric flame shapes under the critical conditions for a laminar boundary layer flashback in cylindrical tubes. It has been found that the transformation of the flame shape from a mushroom to a tulip happens in a tube of a given radius, as the thermal expansion coefficient and Le are modified. A smaller Lewis number results in a local increase in the burning rate at the flame tip, with the flame being able to propagate closer to the wall, which significantly increases the flashback propensity, in line with previous findings. In cases with a Lewis number smaller than unity, a higher thermal expansion results in a flame propagation happening closer to the wall, thus facing a weaker oncoming flow and, consequently, becoming more prone to flashback. For Le > 1, the effect of the increase in the thermal expansion coefficient on the flashback tendency is much less pronounced.
      Citation: Fluids
      PubDate: 2024-01-19
      DOI: 10.3390/fluids9010028
      Issue No: Vol. 9, No. 1 (2024)
       
  • Fluids, Vol. 9, Pages 29: The Role of Particle Inertia and Thermal Inertia
           in Heat Transfer in a Non-Isothermal Particle-Laden Turbulent Flow

    • Authors: Hamid Reza Zandi Pour, Michele Iovieno
      First page: 29
      Abstract: We present an analysis of the effect of particle inertia and thermal inertia on the heat transfer in a turbulent shearless flow, where an inhomogeneous passive temperature field is advected along with inertial point particles by a homogeneous isotropic velocity field. Eulerian–Lagrangian direct numerical simulations are carried out in both one- and two-way coupling regimes and analyzed through single-point statistics. The role of particle inertia and thermal inertia is discussed by introducing a new decomposition of particle second-order moments in terms of correlations involving Lagrangian acceleration and time derivative of particles. We present how particle relaxation times mediate the level of particle velocity–temperature correlation, which gives particle contribution to the overall heat transfer. For each thermal Stokes number, a critical Stokes number is individuated. The effect of particle feedback on the attenuation or enhancement of fluid temperature variance is presented. We show that particle feedback enhances fluid temperature variance for Stokes numbers less than one and damps is for larger than one Stokes number, regardless of the thermal Stokes number, even if this effect is amplified by an increasing thermal inertia.
      Citation: Fluids
      PubDate: 2024-01-19
      DOI: 10.3390/fluids9010029
      Issue No: Vol. 9, No. 1 (2024)
       
  • Fluids, Vol. 9, Pages 30: Experimental Analysis of the Influence of the
           Sliding-Gate Valve on Submerged Entry Nozzle Outlet Jets

    • Authors: Jesus Gonzalez-Trejo, Raul Miranda-Tello, Ruslan Gabbasov, Cesar A. Real-Ramirez, Francisco Cervantes-de-la-Torre
      First page: 30
      Abstract: This work studies how the sliding-gate valve (SGV) modifies the features and the dynamic behavior of the outlet jets for flat-bottom and well-bottom bifurcated submerged entry nozzles (SENs) used in continuous casting machines. Three conditions for the SGV were studied: no obstruction, moderate obstruction, and severe obstruction. The experimental study used a scaled model, employing cold water as the working fluid. A high-frequency analysis of the flow inside the SEN’s bore arriving at the outlet ports was performed by employing the particle image velocimetry (PIV) technique. Low-frequency measurements of the volumetric flow at the exit port were obtained by splitting the exit jet into four quadrants and employing digital flowmeters. It was observed that reducing the SGV clearance increases the turbulence of the flow inside the SEN bore, but the flow displays ordered rather than erratic fluctuations. Flowmeter measurements showed that, regardless of the level of obstruction in the SGV, the outlet jets on flat-bottom and the well-bottom SENs have dynamic behaviors and features with significant differences. This finding is relevant because the flow distribution inside the outlet ports is directly related to the jet’s wideness, affecting the recirculation pattern inside the mold and, therefore, the quality of the finished steel slab.
      Citation: Fluids
      PubDate: 2024-01-20
      DOI: 10.3390/fluids9010030
      Issue No: Vol. 9, No. 1 (2024)
       
  • Fluids, Vol. 9, Pages 1: Evaluating the Impact of Domain Boundaries on
           Hemodynamics in Intracranial Aneurysms within the Circle of Willis

    • Authors: Pablo Jeken-Rico, Aurèle Goetz, Philippe Meliga, Aurélien Larcher, Yigit Özpeynirci, Elie Hachem
      First page: 1
      Abstract: Hemodynamic simulations are increasingly used to study vascular diseases such as Intracranial Aneurysms (IA) and to further develop treatment options. However, due to limited data, certain aspects must rely on heuristics, especially at the simulation’s distal ends. In the literature, Murray’s Law is often used to model the outflow split based on vessel cross-section area; however, this poses challenges for the communicating arteries in the Circle of Willis (CoW). In this study, we contribute by assessing the impact of Murray’s Law in patient-specific geometries featuring IA at the posterior communication. We simulate different domain extensions representing common modelling choices and establish Full CoW simulations as a baseline to evaluate the effect of these modelling assumptions on hemodynamic indicators, focusing on IA growth and rupture-related factors such as the Wall Shear Stress (WSS) and Oscillatory Shear Index (OSI). Our findings reveal qualitative alterations in hemodynamics when not modeling posterior communication. Comparisons between computing the anterior circulation and computing the whole Circle of Willis reveal that quantitative changes in WSS may reach up to 80%, highlighting the significance of modelling choices in assessing IA risks and treatment strategies.
      Citation: Fluids
      PubDate: 2023-12-21
      DOI: 10.3390/fluids9010001
      Issue No: Vol. 9, No. 1 (2023)
       
  • Fluids, Vol. 9, Pages 2: Impact of Crustacean Morphology on Metachronal
           Propulsion: A Numerical Study

    • Authors: Enbao Cao, Zbigniew J. Kabala
      First page: 2
      Abstract: Metachrony is defined as coordinated asynchronous movement throughout multiple appendages, such as the cilia of cells and swimmerets of crustaceans. Used by species of crustaceans and microscopic cells to move through fluid, the process of metachronal propulsion was investigated. A rigid crustacean model with paddles moving in symmetric strokes was created to simulate metachronal movement. Coupled with the surrounding fluid domain, the immersed boundary method was employed to analyze the fluid–structure interactions. To explore the effect of a nonlinear morphology on the efficiency of metachronal propulsion, a range of crustacean body shapes was generated and simulated, from upward curves to downward curves. The highest propulsion velocity was found to be achieved when the crustacean model morphology was a downward curve, specifically a parabola of leading coefficient k = −0.4. This curved morphology resulted in a 4.5% higher velocity when compared to the linear model. As k deviated from −0.4, the propulsion velocity decreased with increasing magnitude, forming a concave downward trend. The impact of body shape on propulsion velocity is shown by how the optimal velocity with k = −0.4 is 71.5% larger than the velocity at k = 1. Overall, this study suggests that morphology has a significant impact on metachronal propulsion.
      Citation: Fluids
      PubDate: 2023-12-23
      DOI: 10.3390/fluids9010002
      Issue No: Vol. 9, No. 1 (2023)
       
  • Fluids, Vol. 9, Pages 3: Cavitation Strength, Acoustic Nonlinearity, and
           Gas Bubble Distribution in Water

    • Authors: Alexey V. Bulanov, Ekaterina V. Sosedko, Vladimir A. Bulanov, Igor V. Korskov
      First page: 3
      Abstract: The acoustic properties of real liquids are largely related to the phase inclusions contained in them, of which gas bubbles are the most common. The aim of the work was to find the relationship between the nonlinear acoustic parameter and the cavitation strength of the liquid with the distribution of bubbles in the liquid, which has so far been poorly studied. The theoretical studies of the parameter of acoustic nonlinearity and the cavitation strength of a liquid with bubbles were carried out within the framework of the homogeneous approximation of a micro-homogeneous liquid; the relationship of these parameters with the bubble distribution function was established, and the typical values of these parameters for different concentrations of bubbles were calculated. Experimental measurements of the parameter of acoustic nonlinearity and the cavitation strength in the upper layer of seawater were carried out; these measurements were consistent with the theoretical estimates. A connection was established between the thresholds of acoustic and optical cavitation—the optical breakdown of a liquid by laser radiation. The results obtained can find practical application in the measurement of the cavitation strength of seawater at great depths in the sea, and the use of an optoacoustic method associated with the use of optical cavitation is proposed.
      Citation: Fluids
      PubDate: 2023-12-24
      DOI: 10.3390/fluids9010003
      Issue No: Vol. 9, No. 1 (2023)
       
  • Fluids, Vol. 9, Pages 4: Lower-Dimensional Model of the Flow and Transport
           Processes in Thin Domains by Numerical Averaging Technique

    • Authors: Maria Vasilyeva, Nana Adjoah Mbroh, Mehrube Mehrubeoglu
      First page: 4
      Abstract: In this work, we present a lower-dimensional model for flow and transport problems in thin domains with rough walls. The full-order model is given for a fully resolved geometry, wherein we consider Stokes flow and a time-dependent diffusion–convection equation with inlet and outlet boundary conditions and zero-flux boundary conditions for both the flow and transport problems on domain walls. Generally, discretizations of a full-order model by classical numerical schemes result in very large discrete problems, which are computationally expensive given that sufficiently fine grids are needed for the approximation. To construct a computationally efficient numerical method, we propose a model-order-reduction numerical technique to reduce the full-order model to a lower-dimensional model. The construction of the lower-dimensional model for the flow and the transport problem is based on the finite volume method and the concept of numerical averaging. Numerical results are presented for three test geometries with varying roughness of walls and thickness of the two-dimensional domain to show the accuracy and applicability of the proposed scheme. In our numerical simulations, we use solutions obtained from the finite element method on a fine grid that can resolve the complex geometry at the grid level as the reference solution to the problem.
      Citation: Fluids
      PubDate: 2023-12-25
      DOI: 10.3390/fluids9010004
      Issue No: Vol. 9, No. 1 (2023)
       
  • Fluids, Vol. 9, Pages 5: Magnetohydrodynamic and Ferrohydrodynamic Fluid
           Flow Using the Finite Volume Method

    • Authors: Grigorios Chrimatopoulos, Efstratios E. Tzirtzilakis, Michalis A. Xenos
      First page: 5
      Abstract: Many problems in fluid mechanics describe the change in the flow under the effect of electromagnetic forces. The present study explores the behaviour of an electric conducting, Newtonian fluid flow applying the magnetohydrodynamics (MHD) and ferrohydrodynamics (FHD) principles. The physical problems for such flows are formulated by the Navier–Stokes equations with the conservation of mass and energy equations, which constitute a coupled non-linear system of partial differential equations subject to analogous boundary conditions. The numerical solution of such physical problems is not a trivial task due to the electromagnetic forces which may cause severe disturbances in the flow field. In the present study, a numerical algorithm based on a finite volume method is developed for the solution of such problems. The basic characteristics of the method are, the set of equations is solved using a simultaneous direct approach, the discretization is achieved using the finite volume method, and the solution is attained solving an implicit non-linear system of algebraic equations with intense source terms created by the non-uniform magnetic field. For the validation of the overall algorithm, comparisons are made with previously published results concerning MHD and FHD flows. The advantages of the proposed methodology are that it is direct and the governing equations are not manipulated like other methods such as the stream function vorticity formulation. Moreover, it is relatively easily extended for the study of three-dimensional problems. This study examines the Hartmann flow and the fluid flow with FHD principles, that formulate MHD and FHD flows, respectively. The major component of the Hartmann flow is the Hartmann number, which increases in value the stronger the Lorentz forces are, thus the fluid decelerates. In the case of FHD fluid flow, the major finding is the creation of vortices close to the external magnetic field source, and the stronger the magnetic field of the source, the larger the vortices are.
      Citation: Fluids
      PubDate: 2023-12-25
      DOI: 10.3390/fluids9010005
      Issue No: Vol. 9, No. 1 (2023)
       
  • Fluids, Vol. 9, Pages 6: The Influence of Two-Dimensional Temperature
           Modulation on Floating Droplet Dynamics

    • Authors: Alexander Nepomnyashchy, Ilya Simanovskii
      First page: 6
      Abstract: We investigate the dynamics and instabilities of a droplet that floats on a liquid substrate. The substrate is cooled from below. In the framework of the slender droplet approximation and the precursor model, the problem is studied numerically. Oscillatory and stationary regimes of thermocapillary convection have been observed. The influence of a two-dimensional spatial inhomogeneity of temperature on the droplet dynamics is investigated. The two-dimensional spatial temperature inhomogeneity can suppress oscillations, changing the droplet’s shape. In a definite region of parameters, the two-dimensional spatial modulation can lead to the excitation of periodic oscillations. The influence of the Biot number on the shape of the droplets is studied.
      Citation: Fluids
      PubDate: 2023-12-25
      DOI: 10.3390/fluids9010006
      Issue No: Vol. 9, No. 1 (2023)
       
  • Fluids, Vol. 9, Pages 7: Multiple Steady States in Laminar
           Rayleigh–Bénard Convection of Air

    • Authors: Julien Carlier, Miltiadis V. Papalexandris
      First page: 7
      Abstract: In this article, we report on numerical simulations of laminar Rayleigh–Bénard convection of air in cuboids. We provide numerical evidence of the existence of multiple steady states when the aspect ratio of the cuboid is sufficiently large. In our simulations, the Rayleigh number is fixed at Ra=1.7×104. The gas in the cube is initially at rest but subject to random small-amplitude velocity perturbations and an adverse temperature gradient. When the flow domain is a cube, i.e., the aspect ratio is equal to unity, there is only one steady state. This state is characterized by the development of a single convective roll and by a symmetric normalized temperature profile with respect to the mid-height. On the contrary, when the aspect ratio is equal to 2, there are five different steady states. Only one of them exhibits a symmetric temperature profile and flow structure. The other four steady states are characterized by two-roll configurations and asymmetric temperature profiles.
      Citation: Fluids
      PubDate: 2023-12-26
      DOI: 10.3390/fluids9010007
      Issue No: Vol. 9, No. 1 (2023)
       
  • Fluids, Vol. 9, Pages 8: Study of Insect Impact on an Aerodynamic Body
           Using a Rotary Wing Simulator

    • Authors: Mohammadamin Ghasemzadeh, Alidad Amirfazli
      First page: 8
      Abstract: Laminar flow aircraft may potentially save fuel and reduce the emission of pollutants and greenhouse gases. However, laminar flow aircraft face challenges caused by contaminations on the wings, such as insect impact residue. To study insect residue on an aircraft airfoil, a new setup was developed that used rotary wings and shot an insect toward the leading edge. This setup kept insects intact before impact while airflow was maintained throughout the experiment. Additionally, the setup enabled the long-term observation of the impact residue while the test speed was adjusted. Two experiments were carried out to investigate inconsistencies from past studies about insect rupture velocity and the effect of airflow on residue. Drosophila Hydei was the insect used, and aluminum was used as the baseline substrate, which was also coated with polyurethane, acrylic, and two superhydrophobic coatings. Instead of a threshold velocity for the minimum rupture velocity of the insect, a range from initial insect rupture to the velocity at which insects ruptured in all instances was determined (i.e., 17–30 m/s). Furthermore, the presence of a coating (polyurethane) on the airfoil did not affect the minimum rupture velocity. It was observed that airflow, which has been previously mentioned as a mitigation method, did not change the residue amount after coagulation for all coatings.
      Citation: Fluids
      PubDate: 2023-12-27
      DOI: 10.3390/fluids9010008
      Issue No: Vol. 9, No. 1 (2023)
       
  • Fluids, Vol. 9, Pages 9: Impacts of Mask Wearing and Leakages on Cyclic
           Respiratory Flows and Facial Thermoregulation

    • Authors: Kian Barari, Xiuhua Si, Jinxiang Xi
      First page: 9
      Abstract: Elevated face temperature due to mask wearing can cause discomfort and skin irritation, making mask mandates challenging. When thermal discomfort becomes intolerable, individuals instinctively or unknowingly loosen or remove their facemasks, compromising the mask’s protective efficacy. The objective of this study was to numerically quantify the microclimate under the mask and facial thermoregulation when wearing a surgical mask with different levels of misfit. An integrated ambient–mask–face–airway computational model was developed with gaps of varying sizes and locations and was validated against complementary experiments. The low Reynolds number (LRN) k-ω turbulence model with porous media was used to simulate transient respiratory flows. Both skin convective heat transfer and tissue heat generation were considered in thermoregulation under the facemask, besides the warm air exhaled from the body and the cool air inhaled from the ambient. The results of this study showed that when wearing a surgical mask with a perfect fit under normal breathing, the temperature at the philtrum increased by 4.3 °C compared to not wearing a mask. A small gap measuring 0.51 cm2 (gap A) at the nose top resulted in 5.6% leakage but reduced the warming effect by 28% compared to zero gap. Meanwhile, a gap of 4.3 cm2 (R1L1) caused 42% leakage and a 62% reduction in the warming effect. Unique temporospatial temperature profiles were observed at various sampling points and for different gap sizes, which correlated reasonably with the corresponding flow dynamics, particularly close to the gaps. The temperature change rate also exhibited patterns unique to the gap site and sampling point, with distinctive peaks occurring during the inspiratory–expiratory flow transitions. These results have the significant implications that by using the temporospatial temperature profiles at several landmark points, the gap location can potentially be pinpointed, and the gap size and leakage fractions can be quantified.
      Citation: Fluids
      PubDate: 2023-12-27
      DOI: 10.3390/fluids9010009
      Issue No: Vol. 9, No. 1 (2023)
       
  • Fluids, Vol. 9, Pages 10: Visualization of the Two-Phase Flow Behavior
           Involved in Enhanced Dense Phase Carbon Dioxide Pasteurization by Means of
           High-Speed Imaging

    • Authors: Ratka Hoferick, Holger Schönherr, Stéphan Barbe
      First page: 10
      Abstract: This research explores the two-phase flow behavior involved in enhanced dense phase carbon dioxide inactivation of E. coli DH5α, which has been shown to possess a high microbial reduction efficiency of up to 3.7 ± 0.4 log. We present an experiment in which the liquid sample was pressurized with liquid carbon dioxide to 8.2 MPa and, after saturation, was forced to flow through a mini tube. An experimental setup was developed to visualize the flow patterns (plug, slug and churn flows) occurring in the mini tube by means of high-speed imaging. The values of the wall shear stress were estimated within the mini tube with the help of the gas slug velocities (8–9 m/s) and were compared with threshold shear stress values reported for the disruption of fresh E. coli cells. The results suggest that the preliminary pressurization phase may cause a substantial destabilization of the cell wall of E. coli DH5α.
      Citation: Fluids
      PubDate: 2023-12-27
      DOI: 10.3390/fluids9010010
      Issue No: Vol. 9, No. 1 (2023)
       
  • Fluids, Vol. 9, Pages 11: Volumetric Flow Field inside a Gas Stirred
           Cylindrical Water Tank

    • Authors: Yasmeen Jojo-Cunningham, Xipeng Guo, Chenn Zhou, Yun Liu
      First page: 11
      Abstract: Ladle metallurgy serves as a crucial component of the steelmaking industry, where it plays a pivotal role in manipulating the molten steel to exercise precise control over its composition and properties. Turbulence in ladle metallurgy influences various important aspects of the steelmaking process, including mixing and distribution of additives, alongside the transport and removal of inclusions within the ladle. Consequently, gaining a clear understanding of the stirred flow field holds the potential of optimizing ladle design, improving control strategies, and enhancing the overall efficiency and steel quality. In this project, an advanced Particle-Tracking-Velocimetry system known as “Shake-the-Box” is implemented on a cylindrical water ladle model while compressed air injections through two circular plugs positioned at the bottom of the model are employed to actively stir the flow. To mitigate the particle images distortion caused by the cylindrical plexi-glass walls, the method of refractive matching is utilized with an outer polygon tank filled with a sodium iodide solution. The volumetric flow measurement is achieved on a 6 × 6 × 2 cm domain between the two plugs inside the cylindrical container while the flow rate of gas injection is set from 0.1 to 0.4 L per minute. The volumetric flow field result suggests double gas injection at low flow rate (0.1 L per minute) produce the least disturbed flow while highly disturbed and turbulent flow can be created at higher flow rate of gas injection.
      Citation: Fluids
      PubDate: 2023-12-28
      DOI: 10.3390/fluids9010011
      Issue No: Vol. 9, No. 1 (2023)
       
  • Fluids, Vol. 9, Pages 12: Thermal Transpiration Flow: Molecular Dynamics
           Study from Dense to Dilute Gas

    • Authors: Hiroki Yamaguchi, Gota Kikugawa
      First page: 12
      Abstract: Thermal transpiration flow, a flow from cold to hot, driven by a temperature gradient along a wall under a high Knudsen number condition, was studied using the molecular dynamics method with a two-dimensional channel consisting of infinite parallel plates with nanoscale clearance based on our previous study. To accelerate the numerical analysis, a dense gas was employed in our previous study. In this study, the influence of the number density of gas was investigated by varying the height of the channel while keeping the number of molecules to achieve the flow ranging from dense to dilute gas while maintaining a constant Knudsen number. From the flow velocity profile compared to the number density profile, the thermal transpiration flow was observed for all number density conditions from dense to dilute gas. A similar flow structure was exhibited regardless of the number density. Thus, the numerical analysis in a dense gas condition is considered to be valid and useful for analyzing the thermal transpiration flow.
      Citation: Fluids
      PubDate: 2023-12-30
      DOI: 10.3390/fluids9010012
      Issue No: Vol. 9, No. 1 (2023)
       
  • Fluids, Vol. 9, Pages 13: Computational Fluid Dynamics Modeling of
           Concrete Flows in Drilled Shafts

    • Authors: Jesudoss Aservitham Jeyaraj, Anthony Perez, Abla Zayed, Austin Gray Mullins, Andres E. Tejada-Martinez
      First page: 13
      Abstract: Drilled shafts are cylindrical, cast-in-place concrete deep foundation elements. During construction, anomalies in drilled shafts can occur due to the kinematics of concrete, flowing radially from the center of the shaft to the concrete cover region at the peripheral edge. This radial component of concrete flow develops veins or creases of poorly cemented or high water-cement ratio material, as the concrete flows around the reinforcement cage of rebars and ties, jeopardizing the shaft integrity. This manuscript presents a three-dimensional computational fluid dynamics (CFD) model of the non-Newtonian concrete flow in drilled shaft construction developed using the finite volume method with interface tracking based on the volume of fluid (VOF) method. The non-Newtonian behavior of the concrete is represented via the Carreau constitutive model. The model results are encouraging as the flow obtained from the simulations shows patterns of both horizontal and vertical creases in the concrete cover region, consistent with previously reported field and laboratory experiments. Moreover, the flow exhibits the concrete head differential developed between the inside and the outside of the reinforcement cage, as exhibited in the physical experiments. This head differential induces the radial component of the concrete flow responsible for the creases that develop in the concrete cover region. Results show that the head differential depends on the flowability of the concrete, consistent with field observations. Less viscous concrete tends to reduce the head differential and the formation of creases of poorly cemented material. The model is unique, making use of state-of-the-art numerical techniques and demonstrating the capability of CFD to model industrially relevant concrete flows.
      Citation: Fluids
      PubDate: 2023-12-31
      DOI: 10.3390/fluids9010013
      Issue No: Vol. 9, No. 1 (2023)
       
  • Fluids, Vol. 8, Pages 305: Measurements and Prediction of Ash Deposition
           in a Cyclone-Fired Boiler Operating under Variable Load Conditions

    • Authors: Gautham Krishnamoorthy, Evan Bloom, Krishnamoorthy Viswanathan, Shuchita Sanjay Patwardhan, David John Stadem, Steve Benson
      First page: 305
      Abstract: Measurements of ash deposition rates were made between the secondary superheater and reheater sections of a 450 MW cyclone-fired lignite boiler as the operational load varied from 33 to 100%. Significant reductions in deposition rates with a decrease in operational load were observed. To uncover the causative mechanisms behind these observations, operational data from the power plant were used to carry out computational fluid dynamic (CFD) simulations of the boiler. After ascertaining that the gas temperatures and velocities at various sections within the boiler were being represented adequately, decoupled simulations of the ash deposition process on the deposit probe were carried out using a finely resolved boundary layer mesh. Fly ash particle size distribution (PSD) and its concentration for the decoupled calculations were determined from stand-alone cyclone barrel simulations. The ash partitioning (mass %) between the fly ash and slag was found to be ~50:50, which was in line with previous field observations, and it did not vary significantly across different cyclone loads. The predicted PSD of the deposit ash was concentrated in the size range 10–30 microns, which was in agreement with cross-sectional images of the deposit obtained from the measurements. At lower loads, sharp variations in the deposition rates were predicted in the gas temperature range 950–1150 K. The particle kinetic energy—particle viscosity-based capture methodology utilized in this study in conjunction with appropriate ash compositions, ash viscosity models and gas temperature estimates can help estimate slagging propensities at different loads reasonably well in these systems.
      Citation: Fluids
      PubDate: 2023-11-23
      DOI: 10.3390/fluids8120305
      Issue No: Vol. 8, No. 12 (2023)
       
  • Fluids, Vol. 8, Pages 306: Reducing Scour around Semi-Elliptical Bridge
           Abutments: Application of Roughness Elements

    • Authors: Afsaneh Rezaie, Hossein Afzalimehr, Sina Sohrabi, Mohammad Nazari-Sharabian, Moses Karakouzian, Reza Ahmadi
      First page: 306
      Abstract: Bridge abutments in river channels induce local scour. Recent research indicates that introducing roughness elements on the surface of the bridge abutments can influence the flow pattern around the abutment, reducing the intensity of eddies and diverting the flow away from the abutment. The roughness elements protruding from the abutment surface, with specific thickness, protrusion, and spacing, influence the scour process by enhancing turbulence. This study investigates the impact of roughness elements and their spacing on clear water scour at bridge abutments. The results reveal a noteworthy reduction in scour depth as the spacing between roughness elements decreases and their thickness increases on the abutment surface. Furthermore, an increase in the roughness spacing to roughness protrusion ratio (s/p) leads to an amplified scour depth. Additionally, the presence of roughness on the abutment surface alters the slope characteristics of the scour hole in response to changes in flow depth. In particular, the absence of roughness exhibits an increased slope as flow depth increases, while the presence of roughness results in a reduced slope across all three flow depths examined. Notably, the maximum slope and depth of the scour hole under the influence of roughness elements occurs at angles of 50 to 70 degrees. Also, the slope and depth of the scour hole decrease to a minimum value at specific roughness dimensions (s = 0.17 L and p = 0.17 L).
      Citation: Fluids
      PubDate: 2023-11-25
      DOI: 10.3390/fluids8120306
      Issue No: Vol. 8, No. 12 (2023)
       
  • Fluids, Vol. 8, Pages 307: Portable Air Purifiers’ Predicted
           Efficacy in Mitigating Airborne Pathogen Transmission in an Office Room
           Featuring Mixing Ventilation

    • Authors: Xiangdong Li, Milan J. Patel, Ivan S. Cole
      First page: 307
      Abstract: Portable air purifiers have been extensively used to improve indoor air quality and mitigate the transmission of airborne diseases. However, the efficacy of mitigation is strongly affected by the interactions between jet flows of processed air from the air purifiers and the background airflows driven by the ventilation system. Critical factors in this context include the position and capacity of air purifiers and the ventilation rate of the heating ventilation and air-conditioning (HVAC) system. These factors are investigated in this study via computational fluid dynamics (CFD) simulations and the infection probability for different scenarios is quantified using the latest airborne infection predictive model incorporating recent pathological and clinical data for SARS-CoV-2. The results show that the use of air purifiers can significantly reduce the concentration of particulate matter, thus contributing to a generally lower risk of airborne transmission. However, the position of air purifiers affects their overall efficacy remarkably. Comparatively, a central HVAC system is more efficient at removing airborne particles under an equivalent ventilation rate assuming it uses a mixing ventilation scheme.
      Citation: Fluids
      PubDate: 2023-11-27
      DOI: 10.3390/fluids8120307
      Issue No: Vol. 8, No. 12 (2023)
       
  • Fluids, Vol. 8, Pages 308: Fluid Flow in Helically Coiled Pipes

    • Authors: Leonardo Di G. Sigalotti, Carlos E. Alvarado-Rodríguez, Otto Rendón
      First page: 308
      Abstract: Helically coiled pipes are widely used in many industrial and engineering applications because of their compactness, larger heat transfer area per unit volume and higher efficiency in heat and mass transfer compared to other pipe geometries. They are commonly encountered in heat exchangers, steam generators in power plants and chemical reactors. The most notable feature of flow in helical pipes is the secondary flow (i.e., the cross-sectional circulatory motion) caused by centrifugal forces due to the curvature. Other important features are the stabilization effects of turbulent flow and the higher Reynolds number at which the transition from a laminar to a turbulent state occurs compared to straight pipes. A survey of the open literature on helical pipe flows shows that a good deal of experimental and theoretical work has been conducted to derive appropriate correlations to predict frictional pressure losses under laminar and turbulent conditions as well as to study the dependence of the flow characteristics and heat transfer capabilities on the Reynolds number, the Nusselt number and the geometrical parameters of the helical pipe. Despite the progress made so far in understanding the flow and heat transfer characteristics of helical pipe flow, there is still much work to be completed to address the more complex problem of multiphase flows and the impact of pipe deformation and corrugation on single- and multiphase flow. The aim of this paper is to provide a review on the state-of-the-art experimental and theoretical research concerning the flow in helically coiled pipes.
      Citation: Fluids
      PubDate: 2023-11-27
      DOI: 10.3390/fluids8120308
      Issue No: Vol. 8, No. 12 (2023)
       
  • Fluids, Vol. 8, Pages 309: Effect of a Control Mechanism on the
           Interaction between a Rectangular Jet and a Slotted Plate: Experimental
           Study of the Aeroacoustic Field

    • Authors: Nour Eldin Afyouni, Marwan Alkheir, Hassan Assoum, Bilal El Zohbi, Kamel Abed-Meraim, Anas Sakout, Mouhammad El Hassan
      First page: 309
      Abstract: The aeroacoustic field of a rectangular subsonic jet impinging on a slotted plate was investigated experimentally using microphones and stereoscopic particle image velocimetry (S-PIV). The study was carried out with a Reynolds number of 6700 and an impact distance of 4 cm. The current configuration represents a benchmark standpoint, featuring high levels of generated noise. A control mechanism consisting of a thin rod was introduced downstream from the jet exit to suppress the self-sustained tones. A total of 1085 positions of the rod between the jet exit and impinging plate were tested to identify positions of optimal noise reduction. Two zones were distinguished in terms of control efficacy: a zone where the sound pressure level (SPL) dropped by up to 19 dB and another zone where the SPL increased by up to 14 dB. The velocity fields show that the presence of the rod divides the jet into two lateral secondary jets on both sides of the main jet axis. The outer part of the secondary jets expanded radially with less interaction with the plate compared to the case without the control. This behavior affected the deformation of vortices against the slot. Proper orthogonal decomposition was applied to the velocity field for a better understanding of the turbulence dynamics with and without the control rod.
      Citation: Fluids
      PubDate: 2023-11-28
      DOI: 10.3390/fluids8120309
      Issue No: Vol. 8, No. 12 (2023)
       
  • Fluids, Vol. 8, Pages 310: Numerical Investigation of Critical Hydraulic
           Parameters Using FLOW-3D: A Case Study of Taunsa Barrage, Pakistan

    • Authors: Muhammad Waqas Zaffar, Ishtiaq Haasan, Abdul Razzaq Ghumman
      First page: 310
      Abstract: Hydraulic structures, such as barrages, play an important role in the sustainable development of several regions worldwide. The aim of this novel study is to identify the critical hydraulic parameters (CHPs) of Taunsa Barrage, built on the Indus River. These CHPs, including free surface profiles, flow depths, Froude number, velocity profiles, energy dissipation and turbulence kinetic energy, were investigated using simulation via FLOW-3D numerical models. Incompressible Reynolds-averaged Navier–Stokes (RANS) equations on each computational cell were solved using the numerical methods available in FLOW-3D. The simulation results indicated that the locations of hydraulic jumps (HJs) were lower than that were reported in the previous one-dimensional study. Similarly, the distances of the HJs from the downstream toe of the glacis were reached at 2.97 m and 6 m at 129.10 m and 130.30 m tailwater levels, respectively, which deviated from the previous studies. In higher tailwater, the sequent depth ratio also deviated from the previous data. The maximum turbulent kinetic energies were observed in the developing regions of HJs, which were found to be decreased as the distance from the HJ was increased. The results of this research will be highly useful for engineers working in the field of design of hydraulic structures.
      Citation: Fluids
      PubDate: 2023-11-28
      DOI: 10.3390/fluids8120310
      Issue No: Vol. 8, No. 12 (2023)
       
  • Fluids, Vol. 8, Pages 311: Forced Convection in Porous Medium Using Triply
           Periodical Minimum Surfaces

    • Authors: Mohamad Ziad Saghir, Jordan So, Heba Rasheed, Dauren Ilesaliev
      First page: 311
      Abstract: Recent developments in the 3D printing of metals are attracting many researchers and engineers. Tailoring a porous structure using triply periodic minimum surfaces is becoming an excellent approach for cooling electronic equipment. The availability of metallic 3D printing encourages researchers to study cooling systems using porous media. In the present article, we designed a porous structure using a gyroid model produced using 3D printing. Porous aluminum has a 0.7, 0.8, and 0.9 porosity, respectively. The porous medium is tested experimentally using distilled fluid as the cooling liquid, while the structure is subject to bottom heating with a heat flux of 30,000 W/m2. A different inlet velocity from 0.05 m/s to 0.25 m/s is applied. On the numerical side, the porous medium is modeled as a porous structure, and only the Navier–Stokes equations and the energy equation were solved using the finite element technique. In addition, an excellent agreement between the experimental measurement and numerical calculation, an optimum porosity of 0.8 was obtained. The performance evaluation criterion led us to believe that pressure drop plays a significant role in heat enhancement for this type of gyroid structure. As the porosity increases, the boundary layer becomes more noticeable.
      Citation: Fluids
      PubDate: 2023-11-29
      DOI: 10.3390/fluids8120311
      Issue No: Vol. 8, No. 12 (2023)
       
  • Fluids, Vol. 8, Pages 312: Prediction of Flow Properties of Porous Triply
           Periodic Minimal Surface (TPMS) Structures

    • Authors: Saúl Piedra, Arturo Gómez-Ortega, James Pérez-Barrera
      First page: 312
      Abstract: The flow through geometrically complex structures is an important engineering problem. In this work, the laminar flow through Triply Periodic Minimal Surface (TPMS) structures is numerically analyzed using Computational Fluid Dynamics (CFD) simulations. Two different TPMS structures were designed, and their porosity was characterized as a function of the isovalue. Then, CFD simulations were implemented to compute the pressure drop by systematically varying the flow velocity and the porosity of the structure. A Darcy–Forchheimer model was fitted to CFD results to calculate the inertial and permeability coefficients as functions of the porosity. These types of results can be very useful for designing fluid flow applications and devices (for instance, heat exchangers), as well as for integrating these TPMS structures since the flow can be very well estimated when using the porous medium model.
      Citation: Fluids
      PubDate: 2023-11-29
      DOI: 10.3390/fluids8120312
      Issue No: Vol. 8, No. 12 (2023)
       
  • Fluids, Vol. 8, Pages 313: Research Progress on Active Secondary Jet
           Technology in Supersonic Flow Field of Aerospace Propulsion Systems

    • Authors: Hao Zhu, Haizhou Guo, Junjie Sun, Hui Tian, Guobiao Cai
      First page: 313
      Abstract: As humans continue to explore the aerospace field, higher demands have been placed on new types of propulsion systems. Meanwhile, active secondary flow has been applied to various aspects of engines over the past seventy years, significantly enhancing engine performance. For the new generation of propulsion systems, active secondary flow remains a highly promising technology. This article provides an overview of the application of active secondary flow in engines, including a review of the past research on the secondary jet flow field, and an introduction of the more prominent applications of the jet in engines and its research progress. Finally, the problems existing in the current application of the secondary jet are summarized, and the future direction of the research is anticipated.
      Citation: Fluids
      PubDate: 2023-11-30
      DOI: 10.3390/fluids8120313
      Issue No: Vol. 8, No. 12 (2023)
       
  • Fluids, Vol. 8, Pages 314: Identification of Local Isotropic Turbulence
           

    • Authors: Stoyan Nedeltchev
      First page: 314
      Abstract: Bubble columns (BCs) are widely used in the chemical industry. In many industrial applications, these important gas-liquid contactors operate in a churn-turbulent flow regime. In principle, it is essential to determine the operating conditions in every BC reactor, in which local isotropic turbulence is established. In this work, it was demonstrated that several different parameters (Kolmogorov entropy, correlation dimension and novel hybrid index) follow a monotonic decreasing trend. This finding could be explained by the constantly increasing coalesced bubble size, which brings more order into the gas-liquid system and thus any entropic or chaotic parameter should decrease with the increase in the superficial gas velocity Ug. The profiles of the new parameters in various gas-liquid systems were studied. They were extracted from different pressure signals (gauge or absolute). In this research, BCs of different diameter and equipped with different gas distributors were used. It was demonstrated that the studied parameters could be successfully correlated with the length scale of the micro eddies and thus the Ug range of applicability of the local isotropic turbulence theory under various operating conditions was indirectly determined. The overall gas holdup profiles were analyzed and, based on the exponent of the Ug value, it was found that in the aqueous solutions of alcohols studied, the conditions in the bubble bed (BB) are homogeneous, whereas in the air-tap water system aerated in different BCs, the conditions in the BB are heterogeneous. This result implies that the local isotropic turbulence conditions predominate mainly around the corresponding measurement positions.
      Citation: Fluids
      PubDate: 2023-12-04
      DOI: 10.3390/fluids8120314
      Issue No: Vol. 8, No. 12 (2023)
       
  • Fluids, Vol. 8, Pages 315: Transporting Particles with Vortex Rings

    • Authors: Van Gulinyan, Fedor Kuzikov, Roman Podgornyi, Daniil Shirkin, Ivan Zakharov, Zarina Sadrieva, Maxim Korobkov, Yana Muzychenko, Andrey Kudlis
      First page: 315
      Abstract: Due to their long-lived nature, vortex rings are highly promising for the non-contact transportation of colloidal microparticles. However, because of the high complexity of the structures, their description using rigorous, closed-form mathematical expressions is challenging, particularly in the presence of strongly inhomogeneous colloidal suspensions. In this work, we comprehensively study this phenomenon, placing special emphasis on a quantitative description of the ability of vortex rings to move the particles suspended in a liquid over distances significantly exceeding the ring’s dimensions. Moreover, within the study, we present straightforward analytical approximations extracted by using the fitting of the experimental and numerical simulation observations that reveal the dynamics of vortex rings transporting the microparticles. It includes both the dependence of the concentration on the distance traveled by the vortex ring and coefficients describing the evolution of vortex ring shape in time, which were not presented in the literature before. It turns out that despite the fact that 2D modeling is a simplification of the full 3D problem solution and is unable to capture some of the minor effects of real behavior, it has demonstrated a good consistency with the results obtained via experiments regarding the process of particles transportation.
      Citation: Fluids
      PubDate: 2023-12-05
      DOI: 10.3390/fluids8120315
      Issue No: Vol. 8, No. 12 (2023)
       
  • Fluids, Vol. 8, Pages 316: A Mathematical Model of Blood Loss during Renal
           Resection

    • Authors: James Cowley, Xichun Luo, Grant D. Stewart, Wenmiao Shu, Asimina Kazakidi
      First page: 316
      Abstract: In 2021, approximately 51% of patients diagnosed with kidney tumors underwent surgical resections. One possible way to reduce complications from surgery is to minimise the associated blood loss, which, in the case of partial nephrectomy, is caused by the inadequate repair of branching arteries within the kidney cut during the tumor resection. The kidney vasculature is particularly complicated in nature, consisting of various interconnecting blood vessels and numerous bifurcation, trifurcation, tetrafurcation, and pentafurcation points. In this study, we present a mathematical lumped-parameter model of a whole kidney, assuming a non-Newtonian Carreau fluid, as a first approximation of estimating the blood loss arising from the cutting of single or multiple vessels. It shows that severing one or more blood vessels from the kidney vasculature results in a redistribution of the blood flow rates and pressures to the unaltered section of the kidney. The model can account for the change in the total impedance of the vascular network and considers a variety of multiple cuts. Calculating the blood loss for numerous combinations of arterial cuts allows us to identify the appropriate surgical protocols required to minimise blood loss during partial nephrectomy as well as enhance our understanding of perfusion and account for the possibility of cellular necrosis. This model may help renal surgeons during partial organ resection in assessing whether the remaining vascularisation is sufficient to support organ viability.
      Citation: Fluids
      PubDate: 2023-12-10
      DOI: 10.3390/fluids8120316
      Issue No: Vol. 8, No. 12 (2023)
       
  • Fluids, Vol. 8, Pages 317: A Constructal-Theory-Based Methodology to
           Determine the Configuration of Empty Channels Used in the Resin
           Impregnation of a Square Porous Plate

    • Authors: Glauciléia Maria Cardoso Magalhães, Jeferson Avila Souza, Elizaldo Domingues dos Santos
      First page: 317
      Abstract: Liquid composite molding techniques are largely used to produce pieces such as truck cabins or wind turbine blades. The liquid resin infusion processes use a network of injection channels to improve the resin flow through a porous-reinforced medium. The present numerical study predicts the positioning of empty channels by applying constructal theory to an idealized problem. The channels’ position and size were not predefined but instead constructed (made to grow) from an elemental channel. Two strategies were tested for channel growth: each new elemental channel was placed next to the region with the lowest or highest resistance to resin flow. The geometric configuration of the channels was constructed using a control function instead of using pre-defined shapes. The conservation of mass and momentum and an additional transport equation for the resin volume fraction were solved using the finite volume method. The volume of the fluid model was used for the treatment of the multiphase flow (air + resin). The growth of an empty channel with the lowest resistance strategy led to a decrease in the injection time and waste of resin. The size (resolution) of the elemental channel also affected the performance indicators and geometric configuration of the injection channels.
      Citation: Fluids
      PubDate: 2023-12-10
      DOI: 10.3390/fluids8120317
      Issue No: Vol. 8, No. 12 (2023)
       
  • Fluids, Vol. 8, Pages 318: Demonstrating the Kelvin-Helmholtz Instability
           Using a Low-Cost Experimental Apparatus and Computational Fluid Dynamics
           Simulations

    • Authors: Melissa M. Gibbons, Dillon Muldoon, Imane Khalil
      First page: 318
      Abstract: A Kelvin-Helmholtz instability is formed when two fluids of different densities exert a shear on one another at their interface when flowing in opposite directions. This paper presents a step-by-step guide for the design of a low-cost, small-scale, experimental tilt tube apparatus and a corresponding computational fluid dynamics (CFD) model that can be used to introduce the Kelvin-Helmholtz instability to undergraduate mechanical engineering students in several courses. A thermal-fluids laboratory course is taken by our fourth-year mechanical engineering students, and the overall variety of experiments has been limited by the cost of commercial teaching equipment. The tilt tube apparatus allows students to induce and record the Kelvin-Helmholtz instability, and no ongoing costs are involved in incorporating this experiment into the course. In our introductory CFD course, students perform CFD simulations as part of the design and analysis process. Developing a two-dimensional (2D) CFD model with two different fluids is well within their capabilities after completing initial software and simulation tutorial exercises and homework. Representative experiments were conducted with fresh water and salt water of different densities, and results showed that both the amplitude of the waves and the amount of time the instability was visible decreased with increasing salt water salinity. Results from a 2D CFD model developed in Ansys Fluent exhibited the same trends as the experimental data.
      Citation: Fluids
      PubDate: 2023-12-12
      DOI: 10.3390/fluids8120318
      Issue No: Vol. 8, No. 12 (2023)
       
  • Fluids, Vol. 8, Pages 319: Influence of a Subsidiary Weir on the Stability
           of a Main Structure Built on a Finite Stratum

    • Authors: Yousry Mahmoud Ghazaw, Abdul Razzaq Ghumman, Ahmed Mohammed Sami Al-Janabi, Afzal Ahmed, Erum Aamir, Rana Muhammad Adnan Ikram
      First page: 319
      Abstract: Some dams globally have negatively affected downstream structures. Constructing subsidiary weirs may solve this problem. This novel study focuses on investigating the parameters of seepage beneath the original structure and the proposed subsidiary weir. Conformal mapping and finite element methods are used for the analysis. The proposed subsidiary weir consists of a sloping central apron, flat aprons on both the downstream and upstream ends, and upstream and downstream sheet piles of varying depths. The existing structure also has sheet piles of different depths at its upstream and downstream ends, with an impervious layer situated at a specific depth below both the structures. The study derives equations for the simulation of the upwards pressure on both the structures, seepage rate, and exit gradient along the downstream bed and the filter at an intermediate location. Our own developed software for the analysis and a commercial software for numerical methods named Finite Element Heat Transfer (FEHT)-version-1are used to calculate these parameters. The accuracy of the analytical and numerical methods is verified by comparing the results with experimental data, which demonstrate a good level of agreement. This study also simulates the impacts of various factors, such as sheet pile configurations, the depth of the stratum beneath the structure, the ratio of effective heads, and the length of the intermediate filter.
      Citation: Fluids
      PubDate: 2023-12-15
      DOI: 10.3390/fluids8120319
      Issue No: Vol. 8, No. 12 (2023)
       
  • Fluids, Vol. 8, Pages 320: Flight Dynamic Characteristics of Wide-Body
           Aircraft with Wind Gust and Turbulence

    • Authors: Kashif Mehmood, Syed Irtiza Ali Shah, Taimur Ali Shams, Muhammad Nafees Mumtaz Qadri, Tariq Amin Khan, David Kukulka
      First page: 320
      Abstract: In this research, a wide-body aircraft was analyzed with critical monitoring of its states, a function of several control inputs (wind gust, turbulence, and microburst). The aerodynamic and stability coefficients of a Boeing 747-200 were obtained from previously published works and 6- DOF equations were formulated. Simulations were conducted for various control inputs to determine the aircraft’s free response, as well as the forced response. In order to understand the nature of the atmosphere, three different models were incorporated, including (i) the Dryden Model, (ii) wind gust, and (iii) microburst. The aircraft was found to be stable in the longitudinal and lateral flight modes, with trim conditions agreeing with published data. For a vertical wind gust of −10 ft/s, the AoA and pitch rate were observed to oscillate sinusoidally and became stable with new trim conditions. These states were found to regain trim conditions once the gust was removed. In the case of 3D gust, it was found that the longitudinal modes achieved a new trim condition through Phugoid oscillations, whereas the lateral modes underwent short-period oscillations. For the case of turbulence, random fluctuations were observed for trim conditions with no unstable behavior. When considering the microburst case, it was found that the aircraft initially gained altitude in the region of the headwind; this was followed by a sharp descent under the influence of a vertical velocity component.
      Citation: Fluids
      PubDate: 2023-12-16
      DOI: 10.3390/fluids8120320
      Issue No: Vol. 8, No. 12 (2023)
       
  • Fluids, Vol. 8, Pages 321: Task-Driven Path Planning for Unmanned Aerial
           Vehicle-Based Bridge Inspection in Wind Fields

    • Authors: Yonghu Wang, Chengcheng Duan, Xinyu Huang, Juan Zhao, Ran Zheng, Haiping Li
      First page: 321
      Abstract: Using unmanned aerial vehicles (UAVs) for bridge inspection is becoming increasingly popular due to its ability to improve efficiency and ensure the safety of monitoring personnel. Compared to traditional manual monitoring methods, UAV inspections are a safer and more efficient alternative. This paper examines the impact of meteorological conditions on UAV-based bridge monitoring during specific tasks, with the aim of enhancing the safety of the UAV’s costly components. The wake vortex behind a bridge structure can vary over time due to airflow, which can have a direct impact on the safety of UAV flights. To assess this impact, numerical analysis is conducted based on monitoring requirements specific to different tasks, taking into account wind speed, wind direction, and air temperature. In order to optimize UAV trajectory, it is important to consider the wake vortex intensity and its associated influence region, which can pose a potential danger to UAV flight. Additionally, the analysis should take into account the aerodynamic effects of different types of bridge columns on the wake vortex. An optimization algorithm was utilized to optimize the trajectory of a UAV during bridge inspections within the safe region affected by wind fields. This resulted in the determination of an effective and safe flight path. The study reveals that varying wind speeds have an impact on the safe flight zone of UAVs, even if they are below the operational requirements. Therefore, when monitoring bridges using UAVs, it is important to take into account the influence of meteorological conditions. Furthermore, it was observed that the flight path of UAVs during square cylinder column monitoring is longer and more time-consuming than round cylinder column monitoring. Determining an effective UAV inspection path is crucial for completing bridge monitoring tasks in windy conditions, establishing bridge inspection standards, and developing the Intelligent Bridge Inspection System (IBIS).
      Citation: Fluids
      PubDate: 2023-12-16
      DOI: 10.3390/fluids8120321
      Issue No: Vol. 8, No. 12 (2023)
       
  • Fluids, Vol. 8, Pages 322: An Exploratory Wind Tunnel Study of Air Jet
           Wheel Spoilers

    • Authors: Jeff Howell, Daniel Butcher, Martin Passmore
      First page: 322
      Abstract: Wheels and wheelhouses are a significant source of aerodynamic drag on passenger cars. The use of air jets, in the form of an air curtain, to smooth the airflow around front wheel housings on cars has become common practice, as it produces a small drag benefit. This paper reports an initial small-scale wind tunnel study of an air jet employed as an effective wheel spoiler to reduce the drag produced by the front wheels and wheel housings of passenger cars. For this investigation, the air jet was created using an external compressed-air supply and was applied to a highly simplified car body shape. The data presented suggest that the air jet has some potential as a drag-reduction device.
      Citation: Fluids
      PubDate: 2023-12-18
      DOI: 10.3390/fluids8120322
      Issue No: Vol. 8, No. 12 (2023)
       
  • Fluids, Vol. 8, Pages 323: A Physics-Guided Bi-Fidelity Fourier-Featured
           Operator Learning Framework for Predicting Time Evolution of Drag and Lift
           Coefficients

    • Authors: Amirhossein Mollaali, Izzet Sahin, Iqrar Raza, Christian Moya, Guillermo Paniagua, Guang Lin
      First page: 323
      Abstract: In the pursuit of accurate experimental and computational data while minimizing effort, there is a constant need for high-fidelity results. However, achieving such results often requires significant computational resources. To address this challenge, this paper proposes a deep operator learning-based framework that requires a limited high-fidelity dataset for training. We introduce a novel physics-guided, bi-fidelity, Fourier-featured deep operator network (DeepONet) framework that effectively combines low- and high-fidelity datasets, leveraging the strengths of each. In our methodology, we begin by designing a physics-guided Fourier-featured DeepONet, drawing inspiration from the intrinsic physical behavior of the target solution. Subsequently, we train this network to primarily learn the low-fidelity solution, utilizing an extensive dataset. This process ensures a comprehensive grasp of the foundational solution patterns. Following this foundational learning, the low-fidelity deep operator network’s output is enhanced using a physics-guided Fourier-featured residual deep operator network. This network refines the initial low-fidelity output, achieving the high-fidelity solution by employing a small high-fidelity dataset for training. Notably, in our framework, we employ the Fourier feature network as the trunk network for the DeepONets, given its proficiency in capturing and learning the oscillatory nature of the target solution with high precision. We validate our approach using a well-known 2D benchmark cylinder problem, which aims to predict the time trajectories of lift and drag coefficients. The results highlight that the physics-guided Fourier-featured deep operator network, serving as a foundational building block of our framework, possesses superior predictive capability for the lift and drag coefficients compared to its data-driven counterparts. The bi-fidelity learning framework, built upon the physics-guided Fourier-featured deep operator, accurately forecasts the time trajectories of lift and drag coefficients. A thorough evaluation of the proposed bi-fidelity framework confirms that our approach closely matches the high-fidelity solution, with an error rate under 2%. This confirms the effectiveness and reliability of our framework, particularly given the limited high-fidelity dataset used during training.
      Citation: Fluids
      PubDate: 2023-12-18
      DOI: 10.3390/fluids8120323
      Issue No: Vol. 8, No. 12 (2023)
       
  • Fluids, Vol. 8, Pages 284: Rendering Maxwell Equations into the
           Compressible Inviscid Fluid Dynamics Form

    • Authors: Peter Vadasz
      First page: 284
      Abstract: Maxwell equations governing electromagnetic effects are being shown to be equivalent to the compressible inviscid Navier–Stokes equations applicable in fluid dynamics and representing conservation of mass and linear momentum. The latter applies subject to a generalized Beltrami condition to be satisfied by the magnetic field. This equivalence indicates that the compressible inviscid Navier–Stokes equations are Lorentz invariant as they derive directly from the Lorentz-invariant Maxwell equations subject to the same Beltrami condition, provided the pressure wave propagates at the speed of light, i.e., vo=co. In addition, the derivation and results provide support for the claim that electromagnetic potentials have physical significance as demonstrated by Aharonov–Bohm effect, and are not only a convenient mathematical formulation.
      Citation: Fluids
      PubDate: 2023-10-26
      DOI: 10.3390/fluids8110284
      Issue No: Vol. 8, No. 11 (2023)
       
  • Fluids, Vol. 8, Pages 285: An Enhanced Python-Based Open-Source Particle
           Image Velocimetry Software for Use with Central Processing Units

    • Authors: Ali Shirinzad, Khodr Jaber, Kecheng Xu, Pierre E. Sullivan
      First page: 285
      Abstract: Particle Image Velocimetry (PIV) is a widely used experimental technique for measuring flow. In recent years, open-source PIV software has become more popular as it offers researchers and practitioners enhanced computational capabilities. Software development for graphical processing unit (GPU) architectures requires careful algorithm design and data structure selection for optimal performance. PIV software, optimized for central processing units (CPUs), offer an alternative to specialized GPU software. In the present work, an improved algorithm for the OpenPIV–Python software (Version 0.25.1, OpenPIV, Tel Aviv-Yafo, Israel) is presented and implemented under a traditional CPU framework. The Python language was selected due to its versatility and widespread adoption. The algorithm was also tested on a supercomputing cluster, a workstation, and Google Colaboratory during the development phase. Using a known velocity field, the algorithm precisely captured the time-average flow, momentary velocity fields, and vortices.
      Citation: Fluids
      PubDate: 2023-10-27
      DOI: 10.3390/fluids8110285
      Issue No: Vol. 8, No. 11 (2023)
       
  • Fluids, Vol. 8, Pages 286: Investigations into the Effect of Mixing on
           Steam–Water Two-Phase Subsonic Cross-Flow Stability

    • Authors: Hassan Ali Ghazwani, Khairuddin Sanaullah, Vladimir Vladimirovich Sinitsin, Afrasyab Khan
      First page: 286
      Abstract: Theoretical and experimental aspects of the project were conducted to investigate the effect of the mixing of a swirling steam jet into cross-flowing water. It was observed that based on the theoretical adiabatic estimations for the equilibrium temperature of steam–water mixing and by varying Psteam = 1–3 bar, Pwater = 1 bar and RPM = 60–300 around 97% (experimentally compared to the area it has at initial condition) and 85% (CFD study compared to the area it has at initial condition), an increase in the area under the influence of perfect adiabatic mixing was found. A virtual cover over the steam duct was seen. The area of this virtual cover based on the void fraction of swirling steam had a weak relationship with the total area of the region, inhibiting the perfect mixing for which an analytical relationship had been developed. The effect of mixing on the stability of swirling steam–water cross-flows was overall more than twice that of the effect on the area under the influence of the stability profile protrusions. Thus, an overall rise in inlet pressure contributed to improper mixing, whereas a rise in the RPM contributed to proper mixing inside a fixed window of observations. The effect of spatial scaling of a swirling steam trajectory on mixing in cross-flowing water was also investigated across the vertical plane. Also, the scaling of the vertical trajectories of the swirling steam jets under all operating conditions resulted in merging the regions of perfect mixing to some extent. Thus, the area under the influence of perfect mixing was reduced to around 3–4.7% under all operating conditions with scaling. This type of scaling has enormous potential for the characterization of larger fluid domains in environmental and process engineering studies.
      Citation: Fluids
      PubDate: 2023-10-27
      DOI: 10.3390/fluids8110286
      Issue No: Vol. 8, No. 11 (2023)
       
  • Fluids, Vol. 8, Pages 287: Applicability of the Cox–Merz
           Relationship for Mayonnaise Enriched with Natural Extracts

    • Authors: Somaris E. Quintana, Maria Zuñiga-Navarro, David Ramirez-Brewer, Luis A. García-Zapateiro
      First page: 287
      Abstract: The Cox and Merz rules are empirical correlations between the apparent viscosity of polymers with the effect of shear rate and the complex dynamic viscosity with the effect of frequency. In this study, the rheological properties of mayonnaise-type emulsions enriched with Averrhoa carambola extracts were investigated using small-amplitude oscillatory shear (SAOS) and steady shear flow. The results showed that the shear-thinning behavior of the samples was non-Newtonian with yield stress and had time-dependent characteristics, as evidenced by curves from non-oscillatory measurements. It was observed that the experimental data on the complex and apparent viscosity of the samples obeyed the Cox–Merz rule.
      Citation: Fluids
      PubDate: 2023-10-27
      DOI: 10.3390/fluids8110287
      Issue No: Vol. 8, No. 11 (2023)
       
  • Fluids, Vol. 8, Pages 288: Differential Rotation in Convecting Spherical
           Shells with Non-Uniform Viscosity and Entropy Diffusivity

    • Authors: Parag Gupta, David MacTaggart, Radostin D. Simitev
      First page: 288
      Abstract: Contemporary three-dimensional physics-based simulations of the solar convection zone disagree with observations. They feature differential rotation substantially different from the true rotation inferred by solar helioseismology and exhibit a conveyor belt of convective “Busse” columns not found in observations. To help unravel this so-called “convection conundrum”, we use a three-dimensional pseudospectral simulation code to investigate how radially non-uniform viscosity and entropy diffusivity affect differential rotation and convective flow patterns in density-stratified rotating spherical fluid shells. We find that radial non-uniformity in fluid properties enhances polar convection, which, in turn, induces non-negligible lateral entropy gradients that lead to large deviations from differential rotation geostrophy due to thermal wind balance. We report simulations wherein this mechanism maintains differential rotation patterns very similar to the true solar profile outside the tangent cylinder, although discrepancies remain at high latitudes. This is significant because differential rotation plays a key role in sustaining solar-like cyclic dipolar dynamos.
      Citation: Fluids
      PubDate: 2023-10-27
      DOI: 10.3390/fluids8110288
      Issue No: Vol. 8, No. 11 (2023)
       
  • Fluids, Vol. 8, Pages 289: Reducing Aerodynamic Drag on Flatbed Trailers
           for Passenger Vehicles Using Novel Appendable Devices

    • Authors: Michael Gerard Connolly, Malachy J. O’Rourke, Alojz Ivankovic
      First page: 289
      Abstract: This article presents a study on the aerodynamic drag of a generic dual-axle flatbed trailer and explores ways to reduce the drag using appendable drag-reducing devices. The primary sources of drag originated from the van and trailer’s rear, along with the trailer’s wheels. The most-effective initial device for reducing drag was a full trailer underside cover, which offered a 7% drag reduction. Additionally, ladder racks, dropsides, and rear gates were studied, and it was found that protruding ladder racks significantly increased drag. Rear gates added large amounts of drag and should be removed and stored when not needed. The study also explored novel mid-section devices that increased the van’s base pressure and reduced drag. An axle test revealed that drag for single-, dual-, and triple-axle trailers was very similar in direct flow, but different in yawed flow. A drawbar length test showed a near-linear relationship between drawbar length and drag, manifesting as a 1.7% change in drag per 250 mm change in drawbar length. Several novel modifications were made to the trailer, including fitting six unique appendable devices, which offered a total 7.3% drag reduction. A novel rear van device known as the multi-stage converging cavity was introduced, which reduced drag by nearly 18%. When all the devices were used together, a total 25% drag reduction was observed for the van–trailer combination.
      Citation: Fluids
      PubDate: 2023-10-27
      DOI: 10.3390/fluids8110289
      Issue No: Vol. 8, No. 11 (2023)
       
  • Fluids, Vol. 8, Pages 290: A Computational Study of the Influence of Drag
           Models and Heat Transfer Correlations on the Simulations of Reactive
           Polydisperse Flows in Bubbling Fluidized Beds

    • Authors: Manuel Ernani Cruz, Gabriel Lisbôa Verissimo, Filipe Leite Brandão, Albino José Kalab Leiroz
      First page: 290
      Abstract: In this work, the influence of gas–solid drag and heat transfer coefficient models on the prediction capacity of the Euler–Euler approach to simulate reactive bubbling fluidized bed flows is studied. Three different cases are considered, a non-reactive bidisperse bubbling fluidized bed flow (Case 1), and two reactive polydisperse flows in bubbling fluidized beds, one for biomass gasification (Case 2), and the other for biomass pyrolysis (Case 3). The Gidaspow, Syamlal–O’Brien, and BVK gas–solid drag models and the Gunn, Ranz–Marshall, and Li–Mason gas–solid heat transfer correlations are investigated. A Eulerian multiphase approach in a two-dimensional Cartesian domain is employed for the simulations. Computational results for the three cases are compared with experimental data from the literature. The results obtained here contribute to a better understanding of the impacts of such closure models on the prediction ability of the Euler–Euler approach to simulate reactive flows. The results indicate that, for the simulation of reactive flows in bubbling fluidized bed reactors, the kinetic modeling of the reactions has a global effect, which superposes with the influence of the drag and heat transfer coefficient models. Nevertheless, local parameters can be noticeably affected by the choice of the interface closure models. Finally, this work also identifies the models that lead to the best results for the cases analyzed here, and thus proposes the use of such selected models for gasification and pyrolysis processes occurring in bubbling fluidized bed reactors.
      Citation: Fluids
      PubDate: 2023-10-28
      DOI: 10.3390/fluids8110290
      Issue No: Vol. 8, No. 11 (2023)
       
  • Fluids, Vol. 8, Pages 291: Ultrasonic Bubble Cleaner as a Sustainable
           Solution

    • Authors: Justin Howell, Emerson Ham, Sunghwan Jung
      First page: 291
      Abstract: We aim to develop a floor-cleaning design by exploiting oscillating bubbles combined with ambient pressure waves to clean various surfaces. Previous studies of this method in lab settings have proven its efficacy, but practical applications, especially concerning real-world conditions like dirt surfaces, remain largely unprobed. Our findings indicate that, excluding a configuration with a heavy mass bottom transducer, all tested configurations achieved approximately 60–70% cleaning performance. A slight improvement in cleaning performance was observed with the introduction of microbubbles, although it was within the error margin. Particularly noteworthy is the substantial reduction in water consumption in configurations with a water pocket, decreasing from 280 mL to a mere 3 mL, marking a significant step toward more environmentally sustainable cleaning practices, such as reduced water usage. This research provides implications for real-world cleaning applications, promising an eco-friendly and efficient cleaning alternative that reduces water usage and handles a variety of materials without causing damage.
      Citation: Fluids
      PubDate: 2023-10-28
      DOI: 10.3390/fluids8110291
      Issue No: Vol. 8, No. 11 (2023)
       
  • Fluids, Vol. 8, Pages 292: Radial Basis Function Surrogates for
           Uncertainty Quantification and Aerodynamic Shape Optimization under
           Uncertainties

    • Authors: Varvara Asouti, Marina Kontou, Kyriakos Giannakoglou
      First page: 292
      Abstract: This paper investigates the adequacy of radial basis function (RBF)-based models as surrogates in uncertainty quantification (UQ) and CFD shape optimization; for the latter, problems with and without uncertainties are considered. In UQ, these are used to support the Monte Carlo, as well as, the non-intrusive, Gauss Quadrature and regression-based polynomial chaos expansion methods. They are applied to the flow around an isolated airfoil and a wing to quantify uncertainties associated with the constants of the γ−R˜eθt transition model and the surface roughness (in the 3D case); it is demonstrated that the use of the RBF-based surrogates leads to an up to 50% reduction in computational cost, compared with the same UQ method that uses CFD computations. In shape optimization under uncertainties, solved by stochastic search methods, RBF-based surrogates are used to compute statistical moments of the objective function. In applications with geometric uncertainties which are modeled through the Karhunen–Loève technique, the use on an RBF-based surrogate reduces the turnaround time of an evolutionary algorithm by orders of magnitude. In this type of applications, RBF networks are also used to perform mesh displacement for the perturbed geometries.
      Citation: Fluids
      PubDate: 2023-10-30
      DOI: 10.3390/fluids8110292
      Issue No: Vol. 8, No. 11 (2023)
       
  • Fluids, Vol. 8, Pages 293: Numerical Approach Based on Solving 3D
           Navier–Stokes Equations for Simulation of the Marine Propeller Flow
           Problems

    • Authors: Andrey Kozelkov, Vadim Kurulin, Andrey Kurkin, Andrey Taranov, Kseniya Plygunova, Olga Krutyakova, Aleksey Korotkov
      First page: 293
      Abstract: The report presents the approach implemented in the Russian LOGOS software package for the numerical simulation of the marine propeller flow problems using unstructured computational meshes automatically generated by the mesh generator. This approach includes a computational model based on the Navier–Stokes equation system and written with respect to the physical process: the turbulent nature of flow with transient points is accounted using the Reynolds Averaged Navier–Stokes method and the k–ω SST model of turbulence by Menter along with the γ–Reθ (Gamma Re Theta) laminar-turbulent transition model; the Volume of Fluid method supplemented with the Schnerr–Sauer cavitation model is used to simulate the cavitation processes; a rotating propeller is simulated by a moving computational mesh and the GGI method to provide conformity of the solutions on adjacent boundaries of arbitrarily-shaped unstructured meshes of the two domains. The specific features of the numerical algorithms in use are described. The method validation results are given; they were obtained because of the problems of finding the performance curves of model-scale propellers in open water, namely the problems of finding the performance of propellers KP505 and IB without consideration of cavitation and the performance of propellers VP1304 and C5 under cavitation conditions. The paper demonstrates that the numerical simulation method presented allows for obtaining sufficiently accurate results to predict the main hydrodynamic characteristics for most modes of operation of the propellers.
      Citation: Fluids
      PubDate: 2023-10-31
      DOI: 10.3390/fluids8110293
      Issue No: Vol. 8, No. 11 (2023)
       
  • Fluids, Vol. 8, Pages 294: Analysis of Flow Characteristics of
           Window-Combination-Type Ventilation System Using CFD

    • Authors: Mok-Lyang Cho, Hyeon-Ji Choi, Seo-Jin Kim, Ji-Soo Ha
      First page: 294
      Abstract: In this study, we analyze the performance of ventilation modules to improve air quality in educational facilities. Using (CFD), we examine the flow design variables of a window-mounted ventilation module. Using computational analysis, we analyze various flow design characteristics of window-mounted ventilation modules and review optimal conditions. First, we measure the carbon dioxide concentration in the classroom and use CFD to analyze the internal air characteristics according to the ventilation module’s inflow speed, inflow angle, and indoor temperature conditions. According to classroom air quality management standards, the concentration of carbon dioxide must be managed below 1000 ppm. When the ventilation module’s inflow velocity was 2.0 m/s, a carbon dioxide concentration of less than 1000 ppm was measured in the classroom. Additionally, an air filter was selected to prevent the inflow of external fine dust through the ventilation module. The suitability of HEPA H14 was reviewed to design the weight concentration of fine dust flowing from the ventilation module to be less than 50 μg/m3. Through research, flow design conditions for a window-mounted ventilation module were presented to reduce carbon dioxide concentration inside the classroom. The analysis of the ventilation system flow characteristics proposed in this study derived primary data for improving the classroom ventilation system.
      Citation: Fluids
      PubDate: 2023-11-02
      DOI: 10.3390/fluids8110294
      Issue No: Vol. 8, No. 11 (2023)
       
  • Fluids, Vol. 8, Pages 295: Fluid–Structure Interaction Aortic Valve
           Surgery Simulation: A Review

    • Authors: Alex G. Kuchumov, Anastasiya Makashova, Sergey Vladimirov, Vsevolod Borodin, Anna Dokuchaeva
      First page: 295
      Abstract: The complicated interaction between a fluid flow and a deformable structure is referred to as fluid–structure interaction (FSI). FSI plays a crucial role in the functioning of the aortic valve. Blood exerts stresses on the leaflets as it passes through the opening or shutting valve, causing them to distort and vibrate. The pressure, velocity, and turbulence of the fluid flow have an impact on these deformations and vibrations. Designing artificial valves, diagnosing and predicting valve failure, and improving surgical and interventional treatments all require the understanding and modeling of FSI in aortic valve dynamics. The most popular techniques for simulating and analyzing FSI in aortic valves are computational fluid dynamics (CFD) and finite element analysis (FEA). By studying the relationship between fluid flow and valve deformations, researchers and doctors can gain knowledge about the functioning of valves and possible pathological diseases. Overall, FSI is a complicated phenomenon that has a great impact on how well the aortic valve works. Aortic valve diseases and disorders can be better identified, treated, and managed by comprehending and mimicking this relationship. This article provides a literature review that compiles valve reconstruction methods from 1952 to the present, as well as FSI modeling techniques that can help advance valve reconstruction. The Scopus, PubMed, and ScienceDirect databases were used in the literature search and were structured into several categories. By utilizing FSI modeling, surgeons, researchers, and engineers can predict the behavior of the aortic valve before, during, and after surgery. This predictive capability can contribute to improved surgical planning, as it provides valuable insights into hemodynamic parameters such as blood flow patterns, pressure distributions, and stress analysis. Additionally, FSI modeling can aid in the evaluation of different treatment options and surgical techniques, allowing for the assessment of potential complications and the optimization of surgical outcomes. It can also provide valuable information on the long-term durability and functionality of prosthetic valves. In summary, fluid–structure interaction modeling is an effective tool for predicting the outcomes of aortic valve surgery. It can provide valuable insights into hemodynamic parameters and aid in surgical planning, treatment evaluation, and the optimization of surgical outcomes.
      Citation: Fluids
      PubDate: 2023-11-04
      DOI: 10.3390/fluids8110295
      Issue No: Vol. 8, No. 11 (2023)
       
  • Fluids, Vol. 8, Pages 296: Detonation in van der Waals Gas

    • Authors: Andriy A. Avramenko, Igor V. Shevchuk, Margarita M. Kovetskaya, Yulia Y. Kovetska
      First page: 296
      Abstract: Solving problems of detonation control is associated with obtaining detailed information about the gas dynamics accompanying the detonation process. This paper focuses on the dynamics of real gas flow through a plane detonation wave. The influence of real gas parameters on the Chapman–Jouguet detonation process has been studied. The process is described using the Rankine–Hugoniot system of equations. To model the thermodynamic properties of a real gas, the van der Waals equation of state is used. Equations are obtained to determine the ratio of speeds and pressures during the passage of a wave. The influence of van der Waals parameters on changes in the parameters of the detonation process was elucidated. An increase in parameter A slows down the increase in pressure in the detonation wave, and an increase in parameter B enhances it. Differences in the speed of combustion products for ideal and real gases are shown. For an ideal gas, combustion products flow from the detonation front at a critical (sonic) speed. For a van der Waals gas, the speed of combustion products may be greater than the critical one. Moreover, both factors, additional pressure (A) and additional volume (B), lead to acceleration of combustion products. Effects of heat release on the process parameters were elucidated.
      Citation: Fluids
      PubDate: 2023-11-07
      DOI: 10.3390/fluids8110296
      Issue No: Vol. 8, No. 11 (2023)
       
  • Fluids, Vol. 8, Pages 297: Simulation of Relaxation Processes in
           Hypersonic Flows with One-Temperature Non-Equilibrium Model

    • Authors: Anton Karpenko, Semen Tolstoguzov, Konstantin Volkov
      First page: 297
      Abstract: Steady-state one-dimensional flows of five-component air behind a normal shock wave are considered with a one-temperature model. A mathematical model is formulated to describe the relaxation of a five-component air mixture with a one-temperature non-equilibrium approximation. A numerical study of non-equilibrium flows of a reacting five-component air mixture behind shock waves at different heights and velocities of free flow is performed. The contribution of different types of reactions to the overall relaxation of the mixture is discussed, and the distributions of macro-parameters of the flow behind the shock wave front are calculated. The lengths of the relaxation zones behind the shock wave front are compared at different initial conditions. Calculations are performed for the standard model of atmosphere.
      Citation: Fluids
      PubDate: 2023-11-10
      DOI: 10.3390/fluids8110297
      Issue No: Vol. 8, No. 11 (2023)
       
  • Fluids, Vol. 8, Pages 298: Simulating Flow in an Intestinal Peristaltic
           System: Combining In Vitro and In Silico Approaches

    • Authors: Xinying Liu, Chao Zhong, David F. Fletcher, Timothy A. G. Langrish
      First page: 298
      Abstract: Transport and mixing in the gastric duct occur via peristaltic flow. In vivo data are hard to collect and require strict ethical approval. In contrast, both in vitro and in silico studies allow detailed investigation and can be constructed to answer specific questions. Therefore, the aim of this study was to design a new elastic thermoplastic polyurethane (TPU) intestine model and to compare the flow patterns observed experimentally with those predicted by a Fluid Structure Interaction (FSI) simulation. Here, we present complementary studies that allow feedback to improve both techniques and provide mutual validation. The experimental work provides direct measurement of mixing, and the simulation allows the experimental setup to be studied to determine the impacts of various parameters. We conclude by highlighting the utility of this approach.
      Citation: Fluids
      PubDate: 2023-11-10
      DOI: 10.3390/fluids8110298
      Issue No: Vol. 8, No. 11 (2023)
       
  • Fluids, Vol. 8, Pages 299: Effect of Local Floor Heating System on
           Occupants’ Thermal Comfort and Energy Consumption Using
           Computational Fluid Dynamics (CFD)

    • Authors: Hassan J. Dakkama, Ahmed Jawad Khaleel, Ahmed Qasim Ahmed, Wisam A. M. Al-Shohani, Hayder M. B. Obaida
      First page: 299
      Abstract: In this article, the influence of splitting a local underfloor air distribution system (UFAD) on indoor thermal comfort for three occupants was studied numerically. A validated computational fluid dynamics (CFD) model was employed in this investigation. The proposed heating system was evaluated and analyzed for different values of air temperature and supply velocity. Providing suitable thermal comfort and saving energy are considered the main evaluation indexes for this study. Three cases, cases 2, 3, and 4, of the proposed local UFAD system were compared with a traditional heating system case, case 1. The supplying air velocity and air temperature in the reference case were 0.5 m/s and 29 °C, while in cases 2, 3, and 4, they were 0.4 m/s and 29 °C, 28 °C, and 27 °C, respectively. The results show that acceptable indoor human thermal comfort and energy demand reduction were achieved by using the splitting UFAD concept.
      Citation: Fluids
      PubDate: 2023-11-13
      DOI: 10.3390/fluids8110299
      Issue No: Vol. 8, No. 11 (2023)
       
  • Fluids, Vol. 8, Pages 300: Numerical Simulation of Dropwise Condensation
           

    • Authors: Giulio Croce, Nicola Suzzi
      First page: 300
      Abstract: Dropwise condensation (DWC) of steam over hybrid hydrophobic–hydrophilic surfaces is numerically investigated via a phenomenological, Lagrangian model. The full non-dimensionalization of the heat transfer model, needed to determine the droplet growth, allows for generalization of computational results. Hybrid surfaces characterized by recursive geometries are implemented via the introduction of proper boundary conditions. The numerical size distribution of both the large and the small droplet populations, crucial for development of simplified, statistically sound models, is compared with empirical and theoretical correlations. Then, the validation with experimental data involving DWC over an hybrid surface is successfully conducted and the heat flux is enhanced under different operating conditions via hybrid geometry optimization.
      Citation: Fluids
      PubDate: 2023-11-15
      DOI: 10.3390/fluids8110300
      Issue No: Vol. 8, No. 11 (2023)
       
  • Fluids, Vol. 8, Pages 301: Influence of Weber Number on Crown Morphology
           during an Oblique Droplet Impact on a Thin Wall Film

    • Authors: Jonathan Lukas Stober, Maurizio Santini, Kathrin Schulte
      First page: 301
      Abstract: Spray impacts can be found in several technical applications and consist of many single droplets, which impact under different trajectories on wetted walls. This study investigates the asymmetric crown morphology resulting from an oblique impact (α= 60°) of a single droplet on a horizontal and quiescent wall film of the same liquid. A droplet generator with an accelerated needle releases the droplets (D= 1.5 mm) in a controlled trajectory on a thin film (hf/D= 0.2). The impact process is recorded from two perspectives with two synchronized high-speed cameras. Varying the Weber number within the splashing regime reveals distinct crown morphologies, which are described in detail. For We< 500, a single central finger develops at the front of the crown, with subsequent detachments of secondary droplets. At higher We (>500), a collision of the crown with the wall film shortly after impact introduces disturbances into the rim, leading to two fingers in the middle of the front crown. A further increase in We (>600) intensifies the crown–film interaction, resulting in an early ejection of tiny droplets and a complete breakup of the front rim. The influence of We on the crown morphology during an oblique impact is also compared to the normal impact (90°). This study paves the way for a classification of impact regimes and a comprehensive picture of the oblique impact process, which deserve more investigation.
      Citation: Fluids
      PubDate: 2023-11-16
      DOI: 10.3390/fluids8110301
      Issue No: Vol. 8, No. 11 (2023)
       
  • Fluids, Vol. 8, Pages 302: A Computational Fluid Dynamics Study to Compare
           Two Types of Arterial Cannulae for Cardiopulmonary Bypass

    • Authors: Vera Gramigna, Arrigo Palumbo, Michele Rossi, Gionata Fragomeni
      First page: 302
      Abstract: Thanks to recent technological and IT advances, there have been rapid developments in biomedical and health research applications of computational fluid dynamics. This is a methodology of computer-based simulation that uses numerical solutions of the governing equations to simulate real fluid flows. The aim of this study is to investigate, using a patient-specific computational fluid dynamics analysis, the hemodynamic behavior of two arterial cannulae, with two different geometries, used in clinical practice during cardiopulmonary bypass. A realistic 3D model of the aorta is extracted from a subject’s CT images using segmentation and reverse engineering techniques. The two cannulae, with similar geometry except for the distal end (straight or curved tip), are modeled and inserted at the specific position in the ascending aorta. The assumption of equal boundary conditions is adopted for the two simulations in order to analyze only the effects of a cannula’s geometry on hemodynamic behavior. Simulation results showed a greater percentage of the total output directed towards the supra-aortic vessels with the curved tip cannula (66% vs. 54%), demonstrating that the different cannula tips geometry produces specific advantages during cardiopulmonary bypass. Indeed, the straight one seems to generate a steadier flow pattern with good recirculation in the ascending aorta.
      Citation: Fluids
      PubDate: 2023-11-16
      DOI: 10.3390/fluids8110302
      Issue No: Vol. 8, No. 11 (2023)
       
  • Fluids, Vol. 8, Pages 303: Modeling of Indirect Evaporative Cooling
           Systems: A Review

    • Authors: Roberta Caruana, Stefano De Antonellis, Luca Marocco, Manfredo Guilizzoni
      First page: 303
      Abstract: Air-to-air indirect evaporative cooling (IEC) systems are particular heat exchangers that use the latent heat of evaporation of water to cool down an air stream, without increasing its specific humidity, thus guaranteeing adequate thermohygrometric conditions in the refrigerated environment with low energy consumption. Dew-point indirect evaporative cooling (DIEC) systems are based on the IEC technology, but they recirculate a part of the air taken from the room to be refrigerated, in order to possibly achieve a lower air temperature. IEC and DIEC systems are becoming increasingly common these years, as they can ensure a good efficiency, minimizing the environmental impact of the air-conditioning system. Consequently, it has been necessary to develop models, both analytical and numerical, to quickly and accurately design this type of system and to predict their performance. This paper presents a review of the analytical and numerical models developed specifically for IEC and DIEC systems, highlighting their method, main innovations and advantages, and possible limitations. From this analysis, it emerged that analytical models have been developed since the late 1990s and only few of them are suitable for DIEC heat exchangers, while numerical models for both IEC and DIEC systems are gaining popularity in recent years. Almost all the analyzed models have been validated by comparison with numerical and/or experimental data, showing a maximum discrepancy within 10% in the majority of the cases. However, the validations were performed for a few specific cases, so in real applications it might be difficult to associate the model boundary conditions and the heat exchangers operating conditions, such as nozzles orientations, plates materials, water flow rates, and configurations. Another common limitation concerns the modeling of some properties, as wettability factor and air density, which might affect the accuracy of the results.
      Citation: Fluids
      PubDate: 2023-11-18
      DOI: 10.3390/fluids8110303
      Issue No: Vol. 8, No. 11 (2023)
       
  • Fluids, Vol. 8, Pages 304: BE-BDF2 Time Integration Scheme Equipped with
           Richardson Extrapolation for Unsteady Compressible Flows

    • Authors: Alessandra Nigro
      First page: 304
      Abstract: In this work we investigate the effectiveness of the Backward Euler-Backward Differentiation Formula (BE-BDF2) in solving unsteady compressible inviscid and viscous flows. Furthermore, to improve its accuracy and its order of convergence, we have equipped this time integration method with the Richardson Extrapolation (RE) technique. The BE-BDF2 scheme is a second-order accurate, A-stable, L-stable and self-starting scheme. It has two stages: the first one is the simple Backward Euler (BE) and the second one is a second-order Backward Differentiation Formula (BDF2) that uses an intermediate and a past solution. The RE is a very simple and powerful technique that can be used to increase the order of accuracy of any approximation process by eliminating the lowest order error term(s) from its asymptotic error expansion. The spatial approximation of the governing Navier–Stokes equations is performed with a high-order accurate discontinuous Galerkin (dG) method. The presented numerical results for canonical test cases, i.e., the isentropic convecting vortex and the unsteady vortex shedding behind a circular cylinder, aim to assess the performance of the BE-BDF2 scheme, in its standard version and equipped with RE, by comparing it with the ones obtained by using more classical methods, like the BDF2, the second-order accurate Crank–Nicolson (CN2) and the explicit third-order accurate Strong Stability Preserving Runge–Kutta scheme (SSP-RK3).
      Citation: Fluids
      PubDate: 2023-11-20
      DOI: 10.3390/fluids8110304
      Issue No: Vol. 8, No. 11 (2023)
       
 
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  Subjects -> PHYSICS (Total: 857 journals)
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THERMODYNAMICS (30 journals)

Showing 1 - 29 of 29 Journals sorted alphabetically
Advances in Heat Transfer     Full-text available via subscription   (Followers: 26)
Applied Thermal Engineering     Hybrid Journal   (Followers: 41)
Araucaria. Revista Iberoamericana de Filosofía, Política y Humanidades     Open Access  
Archives of Thermodynamics     Open Access   (Followers: 9)
Chemical Thermodynamics and Thermal Analysis     Open Access   (Followers: 7)
Condensed Matter Physics     Open Access   (Followers: 2)
Diffusion Foundations     Full-text available via subscription   (Followers: 4)
European Journal of Mechanics - B/Fluids     Hybrid Journal   (Followers: 5)
Experimental Heat Transfer     Hybrid Journal   (Followers: 17)
Experimental Thermal and Fluid Science     Hybrid Journal   (Followers: 34)
Fluids     Open Access   (Followers: 1)
Heat and Mass Transfer     Hybrid Journal   (Followers: 28)
Heat Transfer Engineering     Hybrid Journal   (Followers: 37)
High Temperature     Hybrid Journal   (Followers: 2)
HTM Journal of Heat Treatment and Materials     Full-text available via subscription   (Followers: 3)
International Journal of Thermodynamics     Open Access   (Followers: 11)
International Journal of Thermophysics     Hybrid Journal   (Followers: 7)
Journal of Thermodynamics & Catalysis     Open Access   (Followers: 6)
Journal of Chemical Thermodynamics     Hybrid Journal   (Followers: 4)
Journal of Low Temperature Physics     Hybrid Journal   (Followers: 8)
Journal of Non-Newtonian Fluid Mechanics     Hybrid Journal   (Followers: 16)
Journal of Thermal Science     Hybrid Journal   (Followers: 21)
Journal of Thermal Spray Technology     Hybrid Journal   (Followers: 5)
Journal of Thermodynamics     Open Access   (Followers: 7)
Journal of Thermophysics and Heat Transfer     Hybrid Journal   (Followers: 93)
Low Temperature Physics     Hybrid Journal   (Followers: 6)
Metal Science and Heat Treatment     Hybrid Journal   (Followers: 36)
Quantitative InfraRed Thermography Journal     Hybrid Journal  
Thermophysics and Aeromechanics     Hybrid Journal   (Followers: 6)
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School of Mathematical and Computer Sciences
Heriot-Watt University
Edinburgh, EH14 4AS, UK
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