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Fluids
Number of Followers: 1  Open Access journalISSN (Online) 2311-5521 Published by MDPI  [258 journals]
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- Fluids, Vol. 9, Pages 194: Nonlinear Wrinkling Dynamics of a
Multi-Component Vesicle (2D)
Authors: Meng Zhao, Kai Liu
First page: 194
Abstract: This paper investigates wrinkling dynamics of two-dimensional multicomponent vesicles subjected to time-dependent extensional flow. By employing a non-stiff, pseudo-spectral boundary integral approach, we inspect the wrinkling patterns that arise due to negative surface tension and differential bending within a two-phase system. We focus on the formation and evolution of the wrinkling behaviors under diverse phase concentrations, extensional rates, and vesicle sphericity. Our findings demonstrate that for slightly perturbed circular vesicles, the numerical simulations align well with perturbation theory. For elongated vesicles, the wrinkling patterns vary significantly between phases, primarily influenced by their respective bending moduli. In weak flows, buckling behaviors are observed for elongated vesicles, where the membrane bends inward in regions with lower bending modulus.
Citation: Fluids
PubDate: 2024-08-23
DOI: 10.3390/fluids9090194
Issue No: Vol. 9, No. 9 (2024)
- Fluids, Vol. 9, Pages 195: Simulation of Corner Solidification in a Cavity
Using the Lattice Boltzmann Method
Authors: Runa Samanta, Himadri Chattopadhyay
First page: 195
Abstract: This study investigates corner solidification in a closed cavity in which the left and bottom walls are kept at a temperature lower than its initial temperature. The liquid material in the cavity initially lies at its phase transition temperature and, due to cold boundary conditions at the left–bottom walls, solidification starts. The simulation of corner solidification was performed using a kinetic-based lattice Boltzmann method (LBM), and the tracking of the solid–liquid interface was captured through the evaluation of time. The present investigation addresses the effect of natural convection over conduction across a wide range of higher Rayleigh numbers, from 106 to 108. The total-enthalpy-based lattice Boltzmann method (ELBM) was used to observe the thermal profiles in the entire cavity with a two-phase interface. The isotherms reveal the relative dominance of natural convection over conduction, and the pattern of interface reveals the effective growth of the solidified layer in the cavity. To quantify the uniformity of cooling, a coefficient of variation (COV) for the thermal field was calculated in the effective solidified zone at a wide range of Ra. The results show that the value of COV increases with Ra and reduces with time. The thermal instability in the flow field is also quantified through FFT analyses.
Citation: Fluids
PubDate: 2024-08-25
DOI: 10.3390/fluids9090195
Issue No: Vol. 9, No. 9 (2024)
- Fluids, Vol. 9, Pages 196: POD Analysis of the Wake of Two Tandem Square
Cylinders
Authors: Jingcheng Hao, Siva Ramalingam, Md. Mahbub Alam, Shunlin Tang, Yu Zhou
First page: 196
Abstract: This study aims to investigate the wake of two tandem square cylinders based on the Proper Orthogonal Decomposition (POD) analyses of the PIV and hotwire data. The cylinder centre-to-centre spacing ratio L/w examined is from 1.2 to 4.2, covering the four flow regimes, i.e., extended body, reattachment, transition and co-shedding. The Reynolds number examined was 1.3 × 104. A novel Proper Orthogonal Decomposition (POD) technique (hereafter referred to as PODHW) is developed to analyse data from single point hotwire measurements, offering a new perspective compared to the conventional POD analysis (PODPIV) based on Particle Image Velocimetry (PIV) data. A key finding is the identification of two distinct states, reattachment and co-shedding, within the transition flow regime at L/w = 2.8, which PODPIV fails to capture due to the limited duration of the PIV data obtained. This study confirms, for the first time, the existence of these states as proposed by Zhou et al. (2024), highlighting the advantage of using PODHW for capturing intermittent flow phenomena. Furthermore, the analysis reveals how the predominant coherent structures contribute to the total fluctuating velocity energy in each individual regime. Other aspects of the flow are also discussed, including the Strouhal numbers, the contribution to the total fluctuating energy of the flow from the first four POD modes, and a comparison between different regimes.
Citation: Fluids
PubDate: 2024-08-26
DOI: 10.3390/fluids9090196
Issue No: Vol. 9, No. 9 (2024)
- Fluids, Vol. 9, Pages 169: Flowfield and Noise Dynamics of Supersonic
Rectangular Impinging Jets: Major versus Minor Axis Orientations
Authors: Yogesh Mehta, Vikas N. Bhargav, Rajan Kumar
First page: 169
Abstract: The current study explores the flowfield and noise characteristics of an ideally expanded supersonic (Mach 1.44) rectangular jet impinging on a flat surface. The existing literature is primarily concentrated on axisymmetric jets, known for their resonance dominance, pronounced unsteadiness, and acoustic signatures. In contrast, non-axisymmetric jets remain relatively less understood, particularly those impinging on a ground surface. By employing Schlieren imaging, high-frequency pressure measurements using high-bandwidth transducers, and particle image velocimetry (PIV), this research comprehensively examines the flow-acoustic phenomena. Schlieren imaging revealed distinct, coherent structures and strong acoustic waves, while pressure measurements at the impingement surface exhibited high-amplitude fluctuations, peaking at approximately 186 dB. Acoustic analysis identified multiple high-amplitude tones with unique directional characteristics, suggesting the potential for multiple simultaneous modes in rectangular jets. Furthermore, the PIV data elucidated differences in the jet shear layer and wall jet development attributed to the nozzle orientation. These findings contribute to a deeper understanding of non-axisymmetric jet behavior, offering insights relevant to fundamental flow physics and practical applications such as vertical takeoff and landing aircraft.
Citation: Fluids
PubDate: 2024-07-24
DOI: 10.3390/fluids9080169
Issue No: Vol. 9, No. 8 (2024)
- Fluids, Vol. 9, Pages 170: Integrated Aerodynamic Shape and
Aero-Structural Optimization: Applications from Ahmed Body to NACA 0012
Airfoil and Wind Turbine Blades
Authors: Sagidolla Batay, Aigerim Baidullayeva, Erkhan Sarsenov, Yong Zhao, Tongming Zhou, Eddie Yin Kwee Ng, Taldaubek Kadylulu
First page: 170
Abstract: During this research, aerodynamic shape optimization is conducted on the Ahmed body with the drag coefficient as the objective function and the ramp shape as the design variable, while aero-structural optimization is conducted on NACA 0012 to reduce the drag coefficient for the aerodynamic performance with the shape as the design variable while reducing structural mass with the thickness of the panels as the design variables. This is accomplished through a gradient-based optimization process and coupled finite element and computational fluid dynamics (CFD) solvers under fluid–structure interaction (FSI). In this study, DAFoam (Discrete Adjoint with OpenFOAM for High-fidelity Multidisciplinary Design Optimization) and TACS (Toolkit for the Analysis of Composite Structures) are integrated to optimize the aero-structural design of an airfoil concurrently under the FSI condition, with TACS and DAFoam as coupled structural and CFD solvers integrated with a gradient-based adjoint optimization solver. One-way coupling between the fluid and structural solvers for the aero-structural interaction is adopted by using Mphys, a package that standardizes high-fidelity multiphysics problems in OpenMDAO. At the end of the paper, we compare and discuss our findings in the context of existing research, specifically highlighting previous results on the aerodynamic and aero-structural optimization of wind turbine blades.
Citation: Fluids
PubDate: 2024-07-25
DOI: 10.3390/fluids9080170
Issue No: Vol. 9, No. 8 (2024)
- Fluids, Vol. 9, Pages 171: The Effect of Domain Length and Initialization
Noise on Direct Numerical Simulation of Shear Stratified Turbulence
Authors: Vashkar Palma, Daniel MacDonald, Mehdi Raessi
First page: 171
Abstract: Direct numerical simulation (DNS) has been employed with success in a variety of oceanographic applications, particularly for investigating the internal dynamics of Kelvin–Helmholtz (KH) billows. However, it is difficult to relate these results directly with observations of ocean turbulence due to the significant scale differences involved (ocean shear layers are typically on the order of tens to hundreds of meters in thickness, compared to DNS studies, with layers on the order of one to tens of centimeters). As efforts continue to inform our understanding of geophysical-scale turbulence by extrapolating DNS results, it is important to understand the impact of model setup and initial conditions on the resulting turbulent quantities. Given that geophysical-scale measurements, whether through microstructures or other techniques, can only provide estimates of averaged TKE quantities (e.g., TKE dissipation or buoyancy flux), it may be necessary to compare mean turbulent quantities derived from DNS (i.e., across one or more complete billow evolutions) with ocean measurements. In this study, we analyze the effect of domain length and initial velocity noise on resulting turbulent quantities. Domain length is important, as dimensions that are not integer multiples of the natural KH billow wavelength may compress or stretch the billows and impact their energetics. The addition of random noise in the initial velocity field is often used to trigger turbulence and suppress secondary instabilities; however, the impact of noise on the resulting turbulent energetics is largely unknown. In this study, we conclude that domain lengths on the order of 1.5 times the natural wavelength or less can affect the resulting turbulent energetics by a factor of two or more. We also conclude that increasing the amplitude of random initial velocity noise decreases the resulting turbulent energetics, but that different realizations of the random noise field may have an even greater impact than amplitude. These results should be considered when designing a DNS experiment.
Citation: Fluids
PubDate: 2024-07-27
DOI: 10.3390/fluids9080171
Issue No: Vol. 9, No. 8 (2024)
- Fluids, Vol. 9, Pages 172: Numerical Solution of the Newtonian Plane
Couette Flow with Linear Dynamic Wall Slip
Authors: Muner M. Abou Hasan, Ethar A. A. Ahmed, Ahmed F. Ghaleb, Moustafa S. Abou-Dina, Georgios C. Georgiou
First page: 172
Abstract: An efficient numerical approach based on weighted-average finite differences is used to solve the Newtonian plane Couette flow with wall slip, obeying a dynamic slip law that generalizes the Navier slip law with the inclusion of a relaxation term. Slip is exhibited only along the fixed lower plate, and the motion is triggered by the motion of the upper plate. Three different cases are considered for the motion of the moving plate, i.e., constant speed, oscillating speed, and a single-period sinusoidal speed. The velocity and the volumetric flow rate are calculated in all cases and comparisons are made with the results of other methods and available results in the literature. The numerical outcomes confirm the damping with time and the lagging effects arising from the Navier and dynamic wall slip conditions and demonstrate the hysteretic behavior of the slip velocity in following the harmonic boundary motion.
Citation: Fluids
PubDate: 2024-07-27
DOI: 10.3390/fluids9080172
Issue No: Vol. 9, No. 8 (2024)
- Fluids, Vol. 9, Pages 173: Predicting Wall Pressure in Shock Wave/Boundary
Layer Interactions with Convolutional Neural Networks
Authors: Hongyu Wang, Xiaohua Fan, Yanguang Yang, Gang Wang, Feng Xie
First page: 173
Abstract: Within the dynamic realm of variable-geometry shock wave/boundary layer interactions, the wall parameters of the flow field undergo real-time fluctuations. The conventional approach to sensing these changes in wall pressure through sensor measurements is encumbered by a cumbersome process, leading to diminished efficiency and an inability to provide swift predictions of wall parameters. This paper introduces a data-driven methodology that leverages non-contact schlieren imaging to predict wall pressure within the flow field, a technique that holds promise for informing the optimized design of variable-geometry systems. A sophisticated deep learning framework, predicated on Convolutional Neural Networks (CNN), has been engineered to anticipate alterations in wall pressure stemming from high-speed shock wave/boundary layer interactions. Utilizing an impulsive wind tunnel with a Mach number of 6, we have procured a sequence of schlieren images and corresponding wall pressure measurements, capturing the continuous variations induced by an attack angle from a shock wave generator. These data have been instrumental in compiling a comprehensive dataset for the training and evaluation of the CNN. The CNN model, once trained, has adeptly deduced the distribution of wall pressure from the schlieren imagery. Notwithstanding, it was observed that the CNN’s predictive prowess is marginally diminished in regions where pressure variations are most pronounced. To assess the model’s generalization capabilities, we have segmented the dataset according to different temporal intervals for network training. Our findings indicate that while the generalization of all models crafted was less than optimal, Model 4 demonstrated superior generalization. It is thus suggested that augmenting the training set with additional samples and refining the network architecture will be a worthwhile endeavor in subsequent research initiatives.
Citation: Fluids
PubDate: 2024-07-29
DOI: 10.3390/fluids9080173
Issue No: Vol. 9, No. 8 (2024)
- Fluids, Vol. 9, Pages 174: Gradient-Based Aero-Stealth Optimization of a
Simplified Aircraft
Authors: Charles Thoulon, Gilbert Roge, Olivier Pironneau
First page: 174
Abstract: Modern fighter aircraft increasingly need to conjugate aerodynamic performance and low observability. In this paper, we showcase a methodology for a gradient-based bidisciplinary aero-stealth optimization. The shape of the aircraft is parameterized with the help of a CAD modeler, and we optimize it with the SLSQP algorithm. The drag, computed with the help of a RANS method, is used as the aerodynamic criterion. For the stealth criterion, a function is derived from the radar cross-section in a given cone of directions and weighed with a function whose goal is to cancel the electromagnetic intensity in a given direction. Stealth is achieved passively by scattering back the electromagnetic energy away from the radar antenna, and no energy is absorbed by the aircraft, which is considered as a perfect conductor. A Pareto front is identified by varying the weights of the aerodynamic and stealth criteria. The Pareto front allows for an easy identification of the CAD model corresponding to a chosen aero-stealth trade-off.
Citation: Fluids
PubDate: 2024-07-30
DOI: 10.3390/fluids9080174
Issue No: Vol. 9, No. 8 (2024)
- Fluids, Vol. 9, Pages 175: Numerical Study of Laminar Flow and
Vortex-Induced Vibration on Cylinder Subjects to Free and Forced
Oscillation at Low Reynolds Numbers
Authors: M. S. Al Manthari, Carlton Azeez, M. Sankar, B. V. Pushpa
First page: 175
Abstract: In this study, we aimed to numerically investigate the 2D laminar flow over a cylindrical body and performed vortex-induced vibration analyses on a circular cylinder of unit radius placed in a channel, with the cylinder assumed to be fixed. The cases of a cylinder under forced oscillation and three different scenarios of a freely oscillating cylinder were analyzed. The fluid domain dynamics were governed by the incompressible Navier–Stokes equations; however, the structural field was described using nonlinear elastodynamic equations. Fluid and solid domains were discretized with the finite volume method (FVM) in space and time. Predictions of hydrodynamic forces, namely lift and drag terms, were determined for each scenario. An increase in the Reynolds number caused an exponential increment in the lift force. In the case of a stabilized flow, the collective decrease in stiffness and damping decreased the maximal drag and lift factors. Furthermore, it was noticed that the lift factor was minimally altered by variations in damping and stiffness in comparison with the change in the drag factor. From these observations, it appears that the lift factor probably correlates with the cylinder’s structure and fluid properties.
Citation: Fluids
PubDate: 2024-07-30
DOI: 10.3390/fluids9080175
Issue No: Vol. 9, No. 8 (2024)
- Fluids, Vol. 9, Pages 176: Stability or Instability of a Static Liquid
Bridge Appearing in Shaped Crystal Growth from Melt via the Pulling-Down
Method
Authors: Andreea V. Cojocaru, Stefan Balint
First page: 176
Abstract: This study presents sufficient conditions for the stability or instability of the static liquid bridge appearing in crystal growth from the melt of micro-fibers, thin plates, and hollow micro-tubes of predetermined sizes using the pulling-down method. The case in which the contact angle and the growth angle verify the inequality αc>π/2−αg is considered. Experimentally, only stable static liquid bridges can be created; unstable static liquid bridges exist just in theory, because in reality they collapse. The results of this study are significant for shaped crystal growth from melted materials, with given macroscopic dimensions, and using specific equipment. This is because the obtained inequalities represent limits for what can and cannot be achieved experimentally.
Citation: Fluids
PubDate: 2024-07-31
DOI: 10.3390/fluids9080176
Issue No: Vol. 9, No. 8 (2024)
- Fluids, Vol. 9, Pages 177: Dual-Parameter Prediction of Downhole
Supercritical CO2 with Associated Gas Using Levenberg–Marquardt (LM)
Neural Network
Authors: Dedong Xue, Lei Kou, Chunfeng Zheng, Sheng Wang, Shijiao Jia, Chao Yuan
First page: 177
Abstract: This research investigates the application of supercritical carbon dioxide (CO2) within carbon capture, utilization, and storage (CCUS) technologies to enhance oil-well production efficiency and facilitate carbon storage, thereby promoting a low-carbon circular economy. We simulate the flow of supercritical CO2 mixed with associated gas (flow rates 3–13 × 104 Nm3/d) in a miniature venturi tube under high temperature and high-pressure conditions (30–50 MPa, 120–150 °C). Accurate fluid property calculations, essential for simulation fidelity, were performed using the R. Span and W. Wagner and GERG-2008 equations. A dual-parameter prediction model was developed based on the simulation data. However, actual measurements only provide fluid types and measurement data, such as pressure, temperature, and venturi differential pressure, to determine the liquid mass fraction (LMF) and total mass flow rate (m), presenting challenges due to complex nonlinear relationships. Traditional formula-fitting methods proved inadequate for these conditions. Consequently, we employed a Levenberg–Marquardt (LM) based neural network algorithm to address this issue. The LM optimizer excels in handling complex nonlinear problems with faster convergence, making it suitable for our small dataset. Through this approach, we formulated dual-parameter model equations to elucidate fluid flow factors, analyzing the impact of multiple parameters on the LMF and the discharge coefficient (C). The resulting model predicted dual parameters with a relative error for LMF of ±1% (Pc = 95.5%) and for m of ±1% (Pc = 95.5%), demonstrating high accuracy. This study highlights the potential of neural networks to predict the behavior of complex fluids with high supercritical CO2 content, offering a novel solution where traditional methods fail.
Citation: Fluids
PubDate: 2024-07-31
DOI: 10.3390/fluids9080177
Issue No: Vol. 9, No. 8 (2024)
- Fluids, Vol. 9, Pages 178: Bridging Large Eddy Simulation and
Reduced-Order Modeling of Convection-Dominated Flows through Spatial
Filtering: Review and Perspectives
Authors: Annalisa Quaini, Omer San, Alessandro Veneziani, Traian Iliescu
First page: 178
Abstract: Reduced-order models (ROMs) have achieved a lot of success in reducing the computational cost of traditional numerical methods across many disciplines. In fluid dynamics, ROMs have been successful in providing efficient and relatively accurate solutions for the numerical simulation of laminar flows. For convection-dominated (e.g., turbulent) flows, however, standard ROMs generally yield inaccurate results, usually affected by spurious oscillations. Thus, ROMs are usually equipped with numerical stabilization or closure models in order to account for the effect of the discarded modes. The literature on ROM closures and stabilizations is large and growing fast. In this paper, instead of reviewing all the ROM closures and stabilizations, we took a more modest step and focused on one particular type of ROM closure and stabilization that is inspired by large eddy simulation (LES), a classical strategy in computational fluid dynamics (CFD). These ROMs, which we call LES-ROMs, are extremely easy to implement, very efficient, and accurate. Indeed, LES-ROMs are modular and generally require minimal modifications to standard (“legacy”) ROM formulations. Furthermore, the computational overhead of these modifications is minimal. Finally, carefully tuned LES-ROMs can accurately capture the average physical quantities of interest in challenging convection-dominated flows in science and engineering applications. LES-ROMs are constructed by leveraging spatial filtering, which is the same principle used to build classical LES models. This ensures a modeling consistency between LES-ROMs and the approaches that generated the data used to train them. It also “bridges” two distinct research fields (LES and ROMs) that have been disconnected until now. This paper is a review of LES-ROMs, with a particular focus on the LES concepts and models that enable the construction of LES-inspired ROMs and the bridging of LES and reduced-order modeling. This paper starts with a description of a versatile LES strategy called evolve–filter–relax (EFR) that has been successfully used as a full-order method for both incompressible and compressible convection-dominated flows. We present evidence of this success. We then show how the EFR strategy, and spatial filtering in general, can be leveraged to construct LES-ROMs (e.g., EFR-ROM). Several applications of LES-ROMs to the numerical simulation of incompressible and compressible convection-dominated flows are presented. Finally, we draw conclusions and outline several research directions and open questions in LES-ROM development. While we do not claim this review to be comprehensive, we certainly hope it serves as a brief and friendly introduction to this exciting research area, which we believe has a lot of potential in the practical numerical simulation of convection-dominated flows in science, engineering, and medicine.
Citation: Fluids
PubDate: 2024-08-04
DOI: 10.3390/fluids9080178
Issue No: Vol. 9, No. 8 (2024)
- Fluids, Vol. 9, Pages 179: Characterization of the Three-Dimensional
Flowfield over a Truncated Linear Aerospike
Authors: Roberto Marsilio, Gaetano Maria Di Cicca, Emanuele Resta, Michele Ferlauto
First page: 179
Abstract: The work focuses on the characterization of the flowfield over a truncated linear aerospike by combining theoretical grounds, numerical simulations and experimental tests. The experimental investigations are carried out on a test rig designed at Politecnico di Torino for advanced nozzle testing. Fully three-dimensional CFD analyses are performed on the actual geometry of the experimental nozzle model. At low nozzle pressure ratios (nprs) the analysis combines numerical simulations and experimental testing, which are also used for validating the CFD results. At higher nprs, the flowfield characterization is performed only by three-dimensional CFD analyses. In addition to the validation of the numerical method, the edge effects at different nprs have been observed.
Citation: Fluids
PubDate: 2024-08-10
DOI: 10.3390/fluids9080179
Issue No: Vol. 9, No. 8 (2024)
- Fluids, Vol. 9, Pages 180: Impact of Navier’s Slip and MHD on a
Hybrid Nanofluid Flow over a Porous Stretching/Shrinking Sheet with Heat
Transfer
Authors: Thippaiah Maranna, Gadhigeppa Myacher Sachin, Ulavathi Shettar Mahabaleshwar, Laura M. Pérez, Igor V. Shevchuk
First page: 180
Abstract: The main objective of this study is to explore the inventive conception of the magnetohydrodynamic flow of a hybrid nanofluid over-porous stretching/shrinking sheet with the effect of radiation and mass suction/injection. The hybrid nanofluid advances both the manufactured nanofluid of the current region and the base fluid. For the current investigation, hybrid nanofluids comprising two different kinds of nanoparticles, aluminium oxide and ferrofluid, contained in water as a base fluid, are considered. A collection of highly nonlinear partial differential equations is used to model the whole physical problem. These equations are then transformed into highly nonlinear ordinary differential equations using an appropriate similarity technique. The transformed differential equations are nonlinear, and thus it is difficult to analytically solve considering temperature increases. Then, the outcome is described in incomplete gamma function form. The considered physical parameters namely, magnetic field, Inverse Darcy number, velocity slip, suction/injection, temperature jump effects on velocity, temperature, skin friction and Nusselt number profiles are reviewed using plots. The results reveal that magnetic field, and Inverse Darcy number values increase as the momentum boundary layer decreases. Moreover, higher values of heat sources and thermal radiation enhance the thermal boundary layer. The present problem has various applications in manufacturing and technological devices such as cooling systems, condensers, microelectronics, digital cooling, car radiators, nuclear power stations, nano-drag shipments, automobile production, and tumour treatments.
Citation: Fluids
PubDate: 2024-08-10
DOI: 10.3390/fluids9080180
Issue No: Vol. 9, No. 8 (2024)
- Fluids, Vol. 9, Pages 181: Pressure Drop Estimation of Two-Phase Adiabatic
Flows in Smooth Tubes: Development of Machine Learning-Based Pipelines
Authors: Farshad Bolourchifard, Keivan Ardam, Farzad Dadras Javan, Behzad Najafi, Paloma Vega Penichet Domecq, Fabio Rinaldi, Luigi Pietro Maria Colombo
First page: 181
Abstract: The current study begins with an experimental investigation focused on measuring the pressure drop of a water–air mixture under different flow conditions in a setup consisting of horizontal smooth tubes. Machine learning (ML)-based pipelines are then implemented to provide estimations of the pressure drop values employing obtained dimensionless features. Subsequently, a feature selection methodology is employed to identify the key features, facilitating the interpretation of the underlying physical phenomena and enhancing model accuracy. In the next step, utilizing a genetic algorithm-based optimization approach, the preeminent machine learning algorithm, along with its associated optimal tuning parameters, is determined. Ultimately, the results of the optimal pipeline provide a Mean Absolute Percentage Error (MAPE) of 5.99% on the validation set and 7.03% on the test. As the employed dataset and the obtained optimal models will be opened to public access, the present approach provides superior reproducibility and user-friendliness in contrast to existing physical models reported in the literature, while achieving significantly higher accuracy.
Citation: Fluids
PubDate: 2024-08-11
DOI: 10.3390/fluids9080181
Issue No: Vol. 9, No. 8 (2024)
- Fluids, Vol. 9, Pages 182: Pressure and Velocity Profiles over a Weir
Using Potential Flow Model
Authors: M. R. Ajith Kumar, Prashanth R. Hanmaiahgari, Jaan H. Pu
First page: 182
Abstract: A potential flow model of the semi-inverse type is proposed to simulate flow over round crested weirs. This technique involves the construction of only streamlines over the weir instead of constructing the entire flow net. A Serre–Green–Naghdi (SGN) equation is employed to determine the initial free-surface profile, which is solved using a combined finite volume-finite difference scheme. The potential flow equations were numerically solved using a five-point central finite difference scheme. The model was applied to define the pressure and velocity fields in channel controls involving transcritical flow, such as the Gaussian weir, parabolic weir, and semicircular weir. The impact of streamline curvature on pressure and velocity distributions was investigated in the study. The curvature of the streamline strongly influenced the rise and drop of the bed pressures along the test section. A semicircular weir experiment was also conducted to validate the pressure and velocity profiles obtained using the proposed 2-D fluid flow model. The computed pressure and flow profiles from the solution of the potential flow equation agree perfectly with the present experiment and similar experiments available in the literature. In conclusion, the SGN equation provides an excellent initial profile to solve a 2-D ideal fluid flow numerically.
Citation: Fluids
PubDate: 2024-08-15
DOI: 10.3390/fluids9080182
Issue No: Vol. 9, No. 8 (2024)
- Fluids, Vol. 9, Pages 183: Transient Simulations Based on the Wake of a
Tapered Circular Cylinder
Authors: Jiann-Lin Chen, Shu-Han Hsu, Chun-Lin Chu
First page: 183
Abstract: Numerical techniques have been developed to study flow structures in the wake behind a tapered circular cylinder via computational fluid dynamics. The Reynolds number, based on the mean diameter of the tapered cylinder, is 4 × 103; here, the boundary layer on the cylinder surface is laminar before separating into a turbulent wake. In order to model this transient turbulent flow, a large eddy simulation was adopted and vortex-shedding frequencies were determined using the fast Fourier transform. The fundamental behaviors of the cellular distributions of vortex-shedding frequencies, mechanisms of vortex splitting and the vortex cell reorganization were addressed. Two constant-frequency vortex cells were observed in the operating Reynolds number, and the respective Strouhal numbers were validated experimentally. Numerical flow visualizations showed that the spanwise shedding vortices are well aligned, whereas the vortex splitting seems to disconnect vortex lines. The pressure coefficients at specific zones and angular positions of the tapered cylinder were illustrated to explore the correlation of pressure variation with vortex shedding. The results showed that the vortex splitting initiates and completes at boundary-layer separation. Furthermore, numerical techniques are elaborated on for readers to tackle similar problems.
Citation: Fluids
PubDate: 2024-08-16
DOI: 10.3390/fluids9080183
Issue No: Vol. 9, No. 8 (2024)
- Fluids, Vol. 9, Pages 184: Overview of Pectin-Derived Microparticles
through Microfluidic Technology
Authors: Pedro Brivaldo Viana da Silva, João Paulo Fabi
First page: 184
Abstract: The scientific field of microcarrier systems has gained significant advancements, especially in drug delivery and controlled release mechanisms. This manuscript provides a comprehensive overview of the progress in developing pectin-derived microcarriers fabricated using microfluidic technology. Pectin, a naturally occurring polysaccharide, has garnered attention due to its biocompatibility, biodegradability, and ability to form hydrogels, making it an ideal candidate for forming microcarriers. The integration of microfluidic technology in synthesizing these carriers has revolutionized their design and functionality, enabling precise control over size, morphology, and encapsulation efficiency. This review systematically analyzes the methodologies employed in the microfluidic fabrication of pectin-based microparticles, highlighting the significant advantages this technology offers, such as reduced use of solvents, enhanced reproducibility, and scalability.
Citation: Fluids
PubDate: 2024-08-16
DOI: 10.3390/fluids9080184
Issue No: Vol. 9, No. 8 (2024)
- Fluids, Vol. 9, Pages 185: Proposed Approach for Modelling the
Thermodynamic Behaviour of Entrapped Air Pockets in Water Pipeline
Start-Up
Authors: Dalia M. Bonilla-Correa, Oscar E. Coronado-Hernández, Alfonso Arrieta-Pastrana, Modesto Pérez-Sánchez, Helena M. Ramos
First page: 185
Abstract: Water utilities are concerned about the issue of pipeline collapses, as service interruptions lead to water shortages. Pipeline collapses can occur during the maintenance phase when water columns compress entrapped air pockets, consequently increasing the pressure head. Analysing entrapped air pockets is complex due to the necessity of numerically solving a system of differential equations. Currently, water utilities need more tools to perform this analysis effectively. This research provides a numerical solution to the problem of entrapped air pockets in pipelines which can be utilised to predict filling operations. The study develops an analytical solution to examine the filling process. A practical application is shown, considering a 600 m long pipeline with an internal diameter of 400 mm. Compared with existing mathematical models, the results of the new analytical equations demonstrate their effectiveness as a new tool for computing the main hydraulic and thermodynamic variables involved in this issue.
Citation: Fluids
PubDate: 2024-08-16
DOI: 10.3390/fluids9080185
Issue No: Vol. 9, No. 8 (2024)
- Fluids, Vol. 9, Pages 186: The Use of Computational Fluid Dynamics (CFD)
within the Agricultural Industry to Address General and Manufacturing
Problems
Authors: Navraj Hanspal, Steven A. Cryer
First page: 186
Abstract: Computational fluid dynamics (CFD) is a numerical tool often used to predict anticipated observations using only the physics involved by numerically solving the conservation equations for energy, momentum, and continuity. These governing equations have been around for more than one hundred years, but only limited analytical solutions exist for specific geometries and conditions. CFD provides a numerical solution to these governing equations, and several commercial software and shareware versions exist that provide numerical solutions for customized geometries requiring solutions. Often, experiments are cost prohibitive and/or time consuming, or cannot even be performed, such as the explosion of a chemical plant, downwind air concentrations and the impact on residents and animals, contamination in a river from a point source loading following a train derailment, etc. A modern solution to these problems is the use of CFD to digitally evaluate the output for a given scenario. This paper discusses the use of CFD at Corteva and offers a flavor of the types of problems that can be solved in agricultural manufacturing for pesticides and environmental scenarios in which pesticides are used. Only a handful of examples are provided, but there is a near semi-infinite number of future possibilities to consider.
Citation: Fluids
PubDate: 2024-08-16
DOI: 10.3390/fluids9080186
Issue No: Vol. 9, No. 8 (2024)
- Fluids, Vol. 9, Pages 187: Aeroacoustic Coupling in Rectangular Deep
Cavities: Passive Control and Flow Dynamics
Authors: Abdul Hamid Jabado, Mouhammad El Hassan, Ali Hammoud, Anas Sakout, Hassan H. Assoum
First page: 187
Abstract: Deep cavity configurations are common in various industrial applications, including automotive windows, sunroofs, and many other applications in aerospace engineering. Flows over such a geometry can result in aeroacoustic coupling between the cavity shear layer oscillations and the surrounding acoustic modes. This phenomenon can result in a resonance that can lead to significant noise and may cause damage to mechanical structures. Flow control methods are usually used to reduce or eliminate the aeroacoustic resonance. An experimental set up was developed to study the effectiveness of both a cylinder and a profiled cylinder positioned upstream from the cavity in reducing the flow resonance. The cavity flow and the acoustic signals were obtained using particle image velocimetry (PIV) and unsteady pressure sensors, respectively. A decrease of up to 36 dB was obtained in the sound pressure levels (SPL) using the passive control methods. The profiled cylinder showed a similar efficacy in reducing the resonance despite the absence of a high-frequency forcing. Time-space cross-correlation maps along the cavity shear layer showed the suppression of the feedback mechanism for both control methods. A snapshot proper orthogonal decomposition (POD) showed interesting differences between the cylinder and profiled cylinder control methods in terms of kinetic energy content and the vortex dynamics behavior. Furthermore, the interaction of the wake of the control device with the cavity shear layer and its impact on the aeroacoustic coupling was investigated using the POD analysis.
Citation: Fluids
PubDate: 2024-08-17
DOI: 10.3390/fluids9080187
Issue No: Vol. 9, No. 8 (2024)
- Fluids, Vol. 9, Pages 188: Numerical Analysis of the Submerged Horizontal
Plate Device Subjected to Representative Regular and Realistic Irregular
Waves of a Sea State
Authors: Gabrielle Ücker Thum, Rafael Pereira Maciel, Phelype Haron Oleinik, Luiz Alberto Oliveira Rocha, Elizaldo Domingues dos Santos, Flavio Medeiros Seibt, Bianca Neves Machado, Liércio André Isoldi
First page: 188
Abstract: This study numerically analyzes a submerged horizontal plate (SHP) device subjected to both regular and irregular waves. This device can be used either as a breakwater or a wave energy converter (WEC). The WaveMIMO methodology was applied for the numerical generation and wave propagation of the sea state of the Rio Grande coast in southern Brazil. The finite volume method was employed to solve conservation equations for mass, momentum, and volume fraction transport. The volume of fluid model was employed to handle the water-air mixture. The SHP length (Lp) effects were carried out in five cases. Results indicate that relying solely on regular waves in numerical studies is insufficient for accurately determining the real hydrodynamic behavior. The efficiency of the SHP as a breakwater and WEC varied depending on the wave approach. Specifically, the SHP demonstrates its highest breakwater efficiency in reducing wave height at 2.5Lp for regular waves and 3Lp for irregular waves. As a WEC, it achieves its highest axial velocity at 3Lp for regular waves and 2Lp for irregular waves. Since the literature lacks studies on SHP devices under the incidence of realistic irregular waves, this study significantly contributes to the state of the art.
Citation: Fluids
PubDate: 2024-08-20
DOI: 10.3390/fluids9080188
Issue No: Vol. 9, No. 8 (2024)
- Fluids, Vol. 9, Pages 189: Oscillation of a Liquid Column in an Eccentric
Annulus
Authors: Rajai S. Alassar
First page: 189
Abstract: The velocity distribution of flow in an eccentric cylindrical annulus is determined in an attempt to investigate the vertical capillary rise in the channel. The critical values of the radii ratio and the eccentricity at which the capillary rise changes from oscillatory to monotone or vice versa are determined. For a particular aspect ratio, the rise becomes monotonic as the eccentricity increases. The oscillations are also dampened as the annulus becomes thinner. These critical values depend on Galileo and Bond numbers as well as the contact angle. The results reduce to the limiting cases of concentric and fully eccentric annuli. The critical values are also calculated for the special arrangements when the radii ratios are 1 and 0. The latter limit is in perfect agreement with the conditions found in the literature for the classical circular channel.
Citation: Fluids
PubDate: 2024-08-20
DOI: 10.3390/fluids9080189
Issue No: Vol. 9, No. 8 (2024)
- Fluids, Vol. 9, Pages 190: Performance Prediction of Centrifugal Norm
Pumps Operating as Turbines
Authors: Jasmina Bogdanović-Jovanović, Živojin Stamenković, Miloš Kocić, Jelena Petrović
First page: 190
Abstract: Pump-as-turbines (PAT) has been widely used during the last decade as one of the most interesting technologies in the field of energy recovery. Many studies and papers have been published in which the performance of the pumps in the turbine operating regime were analysed. Since horizontal single stage centrifugal norm pumps are most commonly used as PATs, their performances are analysed in this paper. Most of the research was related to individual pump aggregates or smaller groups and to obtaining their performance curves in turbine random mode. In this work, extensive experimental, numerical, and theoretical investigations were conducted to obtain complete dimensionless performance characteristics of single stage centrifugal norm pumps operating as turbines. One of the goals was to form a simple analytical expression that will, for this type of aggregate, map the pump operating characteristic to the appropriate turbine operating regime. By using the expressions obtained and presented in the paperwork, engineers are enabled to make the appropriate choice of pump aggregate for operation in turbine random mode for potential locations. For this purpose, the procedure for choosing the appropriate PAT aggregate or parallel operation of aggregates and the analysis of their operation on the existing system are presented in the paper. This innovative procedure allows us to select quickly PAT aggregates for a potential location and carry out appropriate techno-economic analyses and analyses of possible energy savings.
Citation: Fluids
PubDate: 2024-08-21
DOI: 10.3390/fluids9080190
Issue No: Vol. 9, No. 8 (2024)
- Fluids, Vol. 9, Pages 191: Strategies for Enhancing One-Equation
Turbulence Model Predictions Using Gene-Expression Programming
Authors: Tony Di Fabbio, Yuan Fang, Eike Tangermann, Richard D. Sandberg, Markus Klein
First page: 191
Abstract: This paper introduces innovative approaches to enhance and develop one-equation RANS models using gene-expression programming. Two distinct strategies are explored: overcoming the limitations of the Boussinesq hypothesis and formulating a novel one-equation turbulence model that can accurately predict a wide range of turbulent wall-bounded flows. A comparative analysis of these strategies highlights their potential for advancing RANS modeling capabilities. The study employs a single-case CFD-driven machine learning framework, demonstrating that machine-informed models significantly improve predictive accuracy, especially when baseline RANS predictions diverge from established benchmarks. Using existing training data, symbolic regression provides valuable insights into the underlying physics by eliminating ineffective strategies. This highlights the broader significance of machine learning beyond developing turbulence closures for specific cases.
Citation: Fluids
PubDate: 2024-08-21
DOI: 10.3390/fluids9080191
Issue No: Vol. 9, No. 8 (2024)
- Fluids, Vol. 9, Pages 192: Transient Shallow Water Wave Interactions with
a Partially Fragmented Ice Shelf
Authors: Faraj Alshahrani, Michael H. Meylan, Ben Wilks
First page: 192
Abstract: This work investigates the interaction between water waves and multiple ice shelf fragments in front of a semi-infinite ice sheet. The hydrodynamics are modelled using shallow water wave theory and the ice shelf vibration is modelled using Euler–Bernoulli beam theory. The ensuing multiple scattering problem is solved in the frequency domain using the transfer matrix method. The appropriate conservation of energy identity is derived in order to validate our numerical calculations. The transient scattering problem for incident wave packets is constructed from the frequency domain solutions. By incorporating multiple scattering, this paper extends previous models that have only considered a continuous semi-infinite ice shelf. This paper serves as a fundamental step towards developing a comprehensive model to simulate the breakup of ice shelves.
Citation: Fluids
PubDate: 2024-08-21
DOI: 10.3390/fluids9080192
Issue No: Vol. 9, No. 8 (2024)
- Fluids, Vol. 9, Pages 193: A Rational Extended Thermodynamic Model for
Nanofluids
Authors: Elvira Barbera, Annamaria Pollino
First page: 193
Abstract: A model of quasilinear differential equations is derived in the context of Rational Extended Thermodynamics to investigate some non-equilibrium phenomena in nanofluids. Following the classical Buongiorno approach, the model assumes nanofluids to be suspensions of two phases: nanoparticles and the base fluid. The field variables are the classical ones and, in addition, the stress tensors and the heat fluxes of both constituents. Balance laws for all field variables are assumed. The obtained system is not closed; therefore, universal physical principles, such as Galilean Invariance and the Entropy Principles, are invoked to close the set of field equations. The obtained model is also written in terms of the whole nanofluid and compared with the classical Buongiorno model. This allowed also the identifications of some parameters in terms of experimental data. The obtained set of field equations has the advantage to recover the Buongiorno model when the phenomena are near equilibrium. At the same time it consists of a hyperbolic set of field equations. Hyperbolicity guarantees finite speeds of propagation and more suitable descriptions of transient regimes. The present model can be used in order to investigate waves, shocks and other phenomena that can be easily described in hyperbolic systems. Furthermore, as a first application and in order to show the potential of the model, stationary 1D solutions are determined and some thermal properties of nanofluids are studied. The solution exhibits, already in the simplest case herein considered, a more accurate evaluation of some fields like the stress tensor components.
Citation: Fluids
PubDate: 2024-08-22
DOI: 10.3390/fluids9080193
Issue No: Vol. 9, No. 8 (2024)
- Fluids, Vol. 9, Pages 147: A Method to Evaluate Forchheimer Resistance
Coefficients for Permeable Screens and Air Louvers Modelled as a Porous
Medium
Authors: Yuriy Marykovskiy, Giulia Pomaranzi, Paolo Schito, Alberto Zasso
First page: 147
Abstract: Porous medium models are commonly used in Computational Fluid Dynamics (CFD) to simulate flow through permeable screens of various types. However, the setup of these models is often limited to replicating a pressure drop in cases where fluid inflow is orthogonal to the screen. In this work, a porous medium formulation that employs a non-diagonal Forchheimer tensor is presented. This formulation is capable of reproducing both the pressure drop and flow deflection under varying inflow angles for complex screen geometries. A general method to determine the porous model coefficients valid for both diagonal and non-diagonal Forchheimer tensors is proposed. The coefficients are calculated using a nonlinear least-squares optimisation based on an analytical solution of a special case of the Navier–Stokes equations. The applicability of the proposed method is evaluated in four different scenarios supplemented by local CFD simulations of permeable screens: wire mesh, perforated screens, air louvers, and expanded mesh panels. The practical application of this method is demonstrated in the modelling of windbreaks and permeable double-skin facades, which typically employ the aforementioned types of porous screens.
Citation: Fluids
PubDate: 2024-06-22
DOI: 10.3390/fluids9070147
Issue No: Vol. 9, No. 7 (2024)
- Fluids, Vol. 9, Pages 148: Flow and Aeroacoustic Characteristics of
Authors: Konstantin Volkov
First page: 148
Abstract: Ensuring the safety of space flights and solving the problems of reducing acoustic loads during the launch of space vehicles requires not only the development of new technical systems for launch complexes, but also methods for the numerical simulation of fluid and aeroacoustic fields generated by supersonic jets. The growing regulations for space vehicle noise also explain the interest in developing models and techniques that anticipate flow and the aeroacoustic characteristics of supersonic jets. Together with integral techniques for computing far-field noise, development of relevant mathematical models and implementation of numerical tools, the concepts of computational fluid dynamics (CFD) and computational aeroacoustics (CAA) are covered. The noise generated by a supersonic underexpanded jet is used to illustrate the capabilities of current numerical modelling and simulation tools. The jet structure, flow properties, and aeroacoustic quantities are affected by the nozzle pressure ratio. The outcomes of numerical simulation are contrasted with existing experimental and computational data. The available numerical modelling and simulation tools facilitate the development of novel computational methods and methodologies for challenges in CFD and CAA, in addition to solving research and engineering problems.
Citation: Fluids
PubDate: 2024-06-22
DOI: 10.3390/fluids9070148
Issue No: Vol. 9, No. 7 (2024)
- Fluids, Vol. 9, Pages 149: Effects of Inlet Velocity Profile on the Bubble
Dynamics in a Fluidized Bed Partially Filled with Geldart B Particles
Authors: Rohit Kanchi, Prashant Singh
First page: 149
Abstract: In this study, a two-dimensional computational domain featuring gas and solid phases is computationally studied for Geldart-B-type particles. In addition to the baseline case of a uniform gas-phase injection velocity, three different inlet velocity profiles were simulated, and their effects on the fluidized bed hydrodynamics and bubble dynamics have been studied. An in-house computer program was developed to track the bubbles and determine the temporal evolution of their size and position prior to their breakup. This program also provides information on the location of bubble coalescence and breakup. The gas-solid interactions were simulated using a Two-Fluid Model (TFM) with Gidaspow’s drag model. The results reveal that the bed hydrodynamics feature a counter-rotating vortex pair for the solid phase, and bubble dynamics, such as coalescence and breakup, can be correlated with the vortices’ outer periphery and the local gradients in the vorticity.
Citation: Fluids
PubDate: 2024-06-22
DOI: 10.3390/fluids9070149
Issue No: Vol. 9, No. 7 (2024)
- Fluids, Vol. 9, Pages 150: Efficiency Improvement of Darrieus Wind Turbine
Using Oscillating Gurney Flap
Authors: Alaeddine Zereg, Mounir Aksas, Mohamed Taher Bouzaher, Salah Laghrouche, Nadhir Lebaal
First page: 150
Abstract: In this work, a new model of Darrieus wind turbines with an oscillating gurney flap (OGF) is proposed. A detailed 2D computational fluid dynamics (CFD) investigation is carried out using ANSYS-Fluent 22.0 to assess the turbine performance. The OGF can alter its position between the upper and lower blade surfaces during the turbine rotation. Equations related to the combined motion are implemented through a user-defined function (UDF). The proposed model is validated where a good coincidence is achieved. The overset dynamic mesh method is used. It was found that a judicious synchronization of OGF and turbine blades creates beneficial vortex interactions, which correct the pressure distribution and lead to an overall improvement in the lift force. The magnitude of the improvement is highly dependent on the OGF length and the phase motion φ. The average torque coefficient Cm for the controlled case increased by more than 19% in comparison with the nominal case.
Citation: Fluids
PubDate: 2024-06-22
DOI: 10.3390/fluids9070150
Issue No: Vol. 9, No. 7 (2024)
- Fluids, Vol. 9, Pages 151: Comparison of Libration- and Precession-Driven
Flows: From Linear Responses to Broadband Dynamics
Authors: Ke Wu, Bruno D. Welfert, Juan M. Lopez
First page: 151
Abstract: Libration and precession are different body forces that are ubiquitous in many rapidly rotating systems, particularly in geophysical and astrophysical flows. Libration is a modulation of the background rotation magnitude, whereas precession is a modulation of the background rotation direction. Assessing the consequences of these body forces in large-scale flows is challenging. The Ekman number, the ratio of the rotation time scale to the viscous time scale quantifying the rotation speed, is extremely small, leading to extremely thin and intense shear layers in the flows even when the amplitudes of the body forces are very small. We consider the consequences of libration and precession numerically in a geometrically simple container, a cube, which lends itself to very efficient, accurate, and robust numerical treatment, with the axis of rotation passing through opposite vertices, so that all walls of the cube are at oblique angles to the rotation axis. This results in the geometric focusing of inertial wavebeams reflecting off the walls, whereby the energy density of the wavebeams increases along with the magnitude of their wavevector. The nature of this focusing depends on the forcing frequency but not on the body force. In the inviscid setting, wavebeams form infinitesimally thin vortex sheets, and their energy density becomes unbounded upon focusing. We present linear inviscid ray tracing to set the scene for the focusing of wavebeams and then consider viscous problems at an Ekman number that is typical of current state-of-the-art laboratory experiments. We begin by considering the linear responses, which are comprised of focusing viscous shear layers, of which their details are mostly captured via ray tracing, and particular solutions accounting for the body forces. These have complicated spatio-temporal structures, which differ for libration and precession. Increasing the forcing amplitude from zero introduces nonlinear interactions, enhances the focusing effects via vortex tilting and stretching when the shear layers reflect at the walls, and also introduces temporal superharmonics and a mean flow. When the magnitude of the mean flow is within a few percent of the magnitude of the instantaneous flow, instabilities breaking the spatio-temporal symmetries set in. These are localized in the oscillatory boundary layers where the reflections are concentrated and introduce broadband dynamics in the boundary layers, with additional inertial wavebeams emitted into the interior. The details again depend on the specifics of the body forces.
Citation: Fluids
PubDate: 2024-06-23
DOI: 10.3390/fluids9070151
Issue No: Vol. 9, No. 7 (2024)
- Fluids, Vol. 9, Pages 152: Minor Loss Coefficient for Abrupt Section
Changes in a Cylindrical Pipe Using a Numerical Approach
Authors: José González, Andrés Meana-Fernández, Iván Vallejo Pérez, Jesús M. Fernández Oro
First page: 152
Abstract: Abrupt section changes are a classic problem in the study of flow in cylindrical ducts or pipes. For its analysis, there are a wide set of exiting data from previous studies, among which some authors stand out and will be mentioned. Those previous works have been used to obtain reliable results for the resolution of section changes along a pipe, either due to cross area increases or reductions on a 1D basis. It is also known that a numerical 2D axisymmetric simulation (CFD) could find a consistent result compared to experimental data in almost all fluid flow fields. The main novelty of the present study is the development of a simple numerical approach used to solve the minor loss calculation. Firstly, a theoretical analysis is developed, and then the results of the numerical simulations carried out on the behavior that affects the water and air flow rate in an abrupt section change, for both contraction and expansion problems, are presented. In both cases, the results are analyzed with different meshes (discretizations) and turbulence models. Finally, the obtained numerical results are compared with those in the technical literature. Also, a theoretical approach is shown in order to show a whole frame of the discussion. The core results are the loss coefficient evolution as a function of the section change both for the sudden contraction and the expansion of a pipe flow. As the results follow the existing experimental values, it is concluded that the developed model provides a feasible and quick design tool to analyze possible geometrical changes without the need for further experiments.
Citation: Fluids
PubDate: 2024-06-26
DOI: 10.3390/fluids9070152
Issue No: Vol. 9, No. 7 (2024)
- Fluids, Vol. 9, Pages 153: Three-Dimensional Physics-Informed Neural
Network Simulation in Coronary Artery Trees
Authors: Nursultan Alzhanov, Eddie Y. K. Ng, Yong Zhao
First page: 153
Abstract: This study introduces a novel approach using 3D Physics-Informed Neural Networks (PINNs) for simulating blood flow in coronary arteries, integrating deep learning with fundamental physics principles. By merging physics-driven models with clinical datasets, our methodology accurately predicts fractional flow reserve (FFR), addressing challenges in noninvasive measurements. Validation against CFD simulations and invasive FFR methods demonstrates the model’s accuracy and efficiency. The mean value error compared to invasive FFR was approximately 1.2% for CT209, 2.3% for CHN13, and 2.8% for artery CHN03. Compared to traditional 3D methods that struggle with boundary conditions, our 3D PINN approach provides a flexible, efficient, and physiologically sound solution. These results suggest that the 3D PINN approach yields reasonably accurate outcomes, positioning it as a reliable tool for diagnosing coronary artery conditions and advancing cardiovascular simulations.
Citation: Fluids
PubDate: 2024-06-27
DOI: 10.3390/fluids9070153
Issue No: Vol. 9, No. 7 (2024)
- Fluids, Vol. 9, Pages 154: Slow Translation of a Composite Sphere in an
Eccentric Spherical Cavity
Authors: Yi C. Chen, Huan J. Keh
First page: 154
Abstract: This semi-analytical study is presented examining the quasi-steady creeping flow caused by a soft (composite) spherical particle, which is a hard (impermeable) sphere core covered by a porous (permeable) layer, translating in an incompressible Newtonian fluid within a non-concentric spherical cavity along the line joining their centers. To solve the Brinkman and Stokes equations for the flow fields inside and outside the porous layer, respectively, general solutions are constructed in two spherical coordinate systems attached to the particle and cavity individually. The boundary conditions at the cavity wall and particle surface are fulfilled through a collocation method. Numerical results of the normalized drag force exerted by the fluid on the particle are obtained for numerous values of the ratios of core-to-particle radii, particle-to-cavity radii, the distance between the centers to the radius difference of the particle and cavity, and the particle radius to porous layer permeation length. For the translation of a soft sphere within a concentric cavity or near a small-curvature cavity wall, our drag results agree with solutions available in the literature. The cavity effect on the drag force of a translating soft sphere is monotonically increasing functions of the ratios of core-to-particle radii and the particle radius to porous layer permeation length. While the drag force generally rises with an increase in the ratio of particle-to-cavity radii, a weak minimum (surprisingly, smaller than that for an unconfined soft sphere) may occur for the case of low ratios of core-to-particle radii and of the particle radius to permeation length. This drag force generally increases with an increase in the eccentricity of the particle position, but in the case of low ratios of core-to-particle radii and particle radius to permeation length, the drag force may decrease slightly with increasing eccentricity.
Citation: Fluids
PubDate: 2024-06-28
DOI: 10.3390/fluids9070154
Issue No: Vol. 9, No. 7 (2024)
- Fluids, Vol. 9, Pages 155: Experimental Investigation of the Performance
of a Novel Ejector–Diffuser System with Different Supersonic Nozzle
Arrays
Authors: Dachuan Xu, Yunsong Gu, Wei Li, Jingxiang Chen
First page: 155
Abstract: The supersonic–supersonic ejector–diffuser system is employed to suck supersonic low-pressure and low-temperature flow into a high-pressure environment. A new design of a supersonic–supersonic ejector–diffuser was introduced to verify pressure control performance under different operating conditions and vacuum background pressure. A 1D analysis was used to predict the geometrical structure of an ejector–diffuser with a rectangular section based on the given operating conditions. Different numbers and types of nozzle plates were designed and installed on the ejector to study the realizability of avoiding or postponing the aerodynamic choking phenomenon in the mixing section. The effects of different geometrical parameters on the operating performance of the ejector–diffuser system were discussed in detail. Experimental investigation of the effects of different types of nozzle plates and the back pressures on the pressure control performance of the designed ejector–diffuser system were performed in a straight-flow wind tunnel. The results showed that the position, type and number of the nozzle plates have a significant impact on the beginning of the formation of aerodynamic choking. The geometry of the ejector and the operating conditions, especially the backpressure and inlet pressure of the ejecting stream, determined the entrainment ratio of the two supersonic streams. The experimental results showed that long nozzle-plate had a better performance in terms of maintaining pressure stability in the test section, while short a nozzle-plate had a better pressure matching performance and could maintain a higher entrainment ratio under high backpressure conditions.
Citation: Fluids
PubDate: 2024-07-02
DOI: 10.3390/fluids9070155
Issue No: Vol. 9, No. 7 (2024)
- Fluids, Vol. 9, Pages 156: Shedding of Cavitation Clouds in an Orifice
Nozzle
Authors: Taihei Onishi, Kaizheng Li, Hong Ji, Guoyi Peng
First page: 156
Abstract: Focused on the unsteady property of a cavitating water jet issuing from an orifice nozzle in a submerged condition, this paper presents a fundamental investigation of the periodicity of cloud shedding and the mechanism of cavitation cloud formation and release by combining the use of high-speed camera observation and flow simulation methods. The pattern of cavitation cloud shedding is evaluated by analyzing sequence images from a high-speed camera, and the mechanism of cloud formation and release is further examined by comparing the results of flow visualization and numerical simulation. It is revealed that one pair of ring-like clouds consisting of a leading cloud and a subsequent cloud is successively shed downstream, and this process is periodically repeated. The leading cloud is principally split by a shear vortex flow along the nozzle exit wall, and the subsequent cloud is detached by a re-entrant jet generated while a fully extended cavity breaks off. The subsequent cavitation cloud catches the leading one, and they coalesce over the range of . Cavitation clouds shed downstream from the nozzle at two dominant frequencies. The Strouhal number of the leading cavitation cloud shedding varies from 0.21 to 0.29, corresponding to the injection pressure. The mass flow rate coefficient fluctuates within the range of at the same frequency as the leading cloud shedding under the effect of cavitation.
Citation: Fluids
PubDate: 2024-07-05
DOI: 10.3390/fluids9070156
Issue No: Vol. 9, No. 7 (2024)
- Fluids, Vol. 9, Pages 157: Design Considerations and Flow Characteristics
for Couette-Type Blood-Shear Devices
Authors: Xingbang Chen, Eldad J. Avital, Shahid Imran, Muhammad Mujtaba Abbas, Patrick Hinkle, Theodosios Alexander
First page: 157
Abstract: Cardiovascular prosthetic devices, stents, prosthetic valves, heart-assist pumps, etc., operate in a wide regime of flows characterized by fluid dynamic flow structures, laminar and turbulent flows, unsteady flow patterns, vortices, and other flow disturbances. These flow disturbances cause shear stress, hemolysis, platelet activation, thrombosis, and other types of blood trauma, leading to neointimal hyperplasia, neoatherosclerosis, pannus overgrowth, etc. Couette-type blood-shearing devices are used to simulate and then clinically measure blood trauma, after which the results can be used to assist in the design of the cardiovascular prosthetic devices. However, previous designs for such blood-shearing devices do not cover the whole range of flow shear, Reynolds numbers, and Taylor numbers characteristic of all types of implanted cardiovascular prosthetic devices, limiting the general applicability of clinical data obtained by tests using different blood-shearing devices. This paper presents the key fluid dynamic parameters that must be met. Based on this, Couette device geometric parameters such as diameter, gap, flow rate, shear stress, and temperature are carefully selected to ensure that the device’s Reynolds numbers, Taylor number, operating temperature, and shear stress in the gap fully represent the flow characteristics across the operating range of all types of cardiovascular prosthetic devices. The outcome is that the numerical data obtained from the presented device can be related to all such prosthetic devices and all flow conditions, making the results obtained with such shearing devices widely applicable across the field. Numerical simulations illustrate that the types of flow patterns generated in the blood-shearing device meet the above criteria.
Citation: Fluids
PubDate: 2024-07-07
DOI: 10.3390/fluids9070157
Issue No: Vol. 9, No. 7 (2024)
- Fluids, Vol. 9, Pages 158: Artificial Intelligence Techniques for the
Hydrodynamic Characterization of Two-Phase Liquid–Gas Flows: An
Overview and Bibliometric Analysis
Authors: July Aandrea Gómez Camperos, Marlon Mauricio Hernández Cely, Aldo Pardo García
First page: 158
Abstract: Accurately and instantly estimating the hydrodynamic characteristics in two-phase liquid–gas flow is crucial for industries like oil, gas, and other multiphase flow sectors to reduce costs and emissions, boost efficiency, and enhance operational safety. This type of flow involves constant slippage between gas and liquid phases caused by a deformable interface, resulting in changes in gas volumetric fraction and the creation of structures known as flow patterns. Empirical and numerical methods used for prediction often result in significant inaccuracies during scale-up processes. Different methodologies based on artificial intelligence (AI) are currently being applied to predict hydrodynamic characteristics in two-phase liquid–gas flow, which was corroborated with the bibliometric analysis where AI techniques were found to have been applied in flow pattern recognition, volumetric fraction determination for each fluid, and pressure gradient estimation. The results revealed that a total of 178 keywords in 70 articles, 29 of which reached the threshold (machine learning, flow pattern, two-phase flow, artificial intelligence, and neural networks as the high predominance), were published mainly in Flow Measurement and Instrumentation. This journal has the highest number of published articles related to the studied topic, with nine articles. The most relevant author is Efteknari-Zadeh, E, from the Institute of Optics and Quantum Electronics.
Citation: Fluids
PubDate: 2024-07-08
DOI: 10.3390/fluids9070158
Issue No: Vol. 9, No. 7 (2024)
- Fluids, Vol. 9, Pages 159: Numerical Simulations of Scalar Transport on
Rough Surfaces
Authors: Zvi Hantsis, Ugo Piomelli
First page: 159
Abstract: Numerical simulations provide unfettered access to details of the flow where experimental measurements are difficult to obtain. This paper summarises the progress achieved in the study of passive scalars in flows over rough surfaces thanks to recent numerical simulations. Townsend’s similarity applies to various scalar statistics, implying the differences due to roughness are limited to the roughness sublayer (RSL). The scalar field exhibits a diffusive sublayer that increasingly conforms to the roughness surface as ks+ or Pr increase. The scalar wall flux is enhanced on the windward slopes of the roughness, where the analogy between momentum and scalar holds well; the momentum and scalar fields, however, have very different behaviours downwind of the roughness elements, due to recirculation, which reduces the scalar wall flux. Roughness causes breakdown of the Reynolds analogy: any increase in St is accompanied by a larger increase in cf. A flattening trend for the scalar roughness function, ΔΘ+, is observed as ks+ increases, suggesting the possibility of a scalar fully rough regime, different from the velocity one. The form-induced (FI) production of scalar fluctuations becomes dominant inside the RSL and is significantly different from the FI production of turbulent kinetic energy, resulting in notable differences between the scalar and velocity fluctuations. Several key questions remain open, in particular regarding the existence of a fully rough scalar regime and its characteristics. With the increase in Re and Pr, various quantities such as scalar roughness function, the dispersive fluxes, FI wall flux, etc., appear to trend towards saturation. However, the limited range of Re and Pr achieved by numerical simulations only allows us to speculate regarding such asymptotic behaviour. Beyond extending the range of Re and Pr, systematic coverage of different roughness types and topologies is needed, as the scalar appears to remain sensitive to the geometrical details.
Citation: Fluids
PubDate: 2024-07-11
DOI: 10.3390/fluids9070159
Issue No: Vol. 9, No. 7 (2024)
- Fluids, Vol. 9, Pages 160: Numerical Study on the Impact Pressure of
Droplets on Wind Turbine Blades Using a Whirling Arm Rain Erosion Tester
Authors: Nobuyuki Fujisawa, Hirokazu Kawabata
First page: 160
Abstract: The leading-edge erosion of a wind turbine blade was tested using a whirling arm rain erosion tester, whose rotation rate is considerably higher than that of a full-scale wind turbine owing to the scale effect. In this study, we assessed the impact pressure of droplets on a wet surface of wind turbine blades using numerical simulation of liquid droplet impact by solving the Navier–Stokes equations combined with the volume-of-fluid method. This was conducted in combination with an estimation of liquid film thickness on the rotating blade using an approximate solution of Navier–Stokes equations considering the centrifugal and Coriolis forces. Our study revealed that the impact pressure on the rain erosion tester exceeded that on the wind turbine blade, attributed to the thinner liquid film on the rain erosion tester than on the wind turbine blade caused by the influence of centrifugal and Coriolis forces. This indicates the importance of correcting the influence of liquid-film thickness in estimating the impact velocity of droplets on the wind turbine blade. Furthermore, we demonstrated the correction procedure when estimating the impact velocity of droplets on the wind turbine blade.
Citation: Fluids
PubDate: 2024-07-15
DOI: 10.3390/fluids9070160
Issue No: Vol. 9, No. 7 (2024)
- Fluids, Vol. 9, Pages 161: Design and Numerical Analysis of an Annular
Combustion Chamber
Authors: Luis Alfonso Moreno-Pacheco, Fernando Sánchez-López, Juan Gabriel Barbosa-Saldaña, José Martínez-Trinidad, Mario Alberto Carpinteyro-Pérez, Wilbert Wong-Ángel, Ricardo Andrés García-León
First page: 161
Abstract: Designing a combustion chamber for gas turbines is considered both a science and an art. This study presents a comprehensive methodology for designing an annular combustion chamber tailored to the operating conditions of a CFM-56 engine, a widely used high bypass ratio turbofan engine. The design process involved calculating the basic criteria and dimensions for the casing, liner, diffuser, and swirl, followed by an analysis of the cooling sections of the liner. Numerical simulations using NUMECA software and the HEXPRESS meshing tool were conducted to predict the combustion chamber’s behavior and performance, employing the κ-ε turbulence model and the Flamelet combustion model. Methane was used as the fuel, and simulations were performed for three fuel injection angles: axial, 45°, and 60°. Results demonstrate that the combustion chamber is properly dimensioned and achieves complete combustion for all configurations. The pressure ratio is 0.96, exceeding the minimum design criteria. Additionally, the emissions of unburned hydrocarbons are zero, while nitrogen oxides and carbon monoxide levels are below regulatory limits. These findings validate the proposed design methodology, ensuring efficient and environmentally compliant combustion chamber performance.
Citation: Fluids
PubDate: 2024-07-16
DOI: 10.3390/fluids9070161
Issue No: Vol. 9, No. 7 (2024)
- Fluids, Vol. 9, Pages 162: A Computational Analysis of Turbocharger
Compressor Flow Field with a Focus on Impeller Stall
Authors: Deb K. Banerjee, Ahmet Selamet, Pranav Sriganesh
First page: 162
Abstract: Understanding the flow instabilities encountered by the turbocharger compressor is an important step toward improving its overall design for performance and efficiency. While an experimental study using Particle Image Velocimetry was previously conducted to examine the flow field at the inlet of the turbocharger compressor, the present work complements that effort by analyzing the flow structures leading to stall instability within the same impeller. Experimentally validated three-dimensional computational fluid dynamics predictions are carried out at three discrete mass flow rates, including 77 g/s (stable, maximum flow condition), 57 g/s (near peak efficiency), and 30 g/s (with strong reverse flow from the impeller) at a fixed rotational speed of 80,000 rpm. Large stationary stall cells were observed deep within the impeller at 30 g/s, occupying a significant portion of the blade passage near the shroud between the suction surface of the main blades and the pressure surface of the splitter blades. These stall cells are mainly created when a substantial portion of the inlet core flow is unable to follow the impeller’s axial to radial bend against the adverse pressure gradient and becomes entrained by the reverse flow and the tip leakage flow, giving rise to a region of low-momentum fluid in its wake. This phenomenon was observed to a lesser extent at 57 g/s and was completely absent at 77 g/s. On the other hand, the inducer rotating stall was found to be most dominant at 57 g/s. The entrainment of the tip leakage flow by the core flow moving into the impeller, leading to the generation of an unstable, wavy shear layer at the inducer plane, was instrumental in the generation of rotating stall. The present analyses provide a detailed characterization of both stationary and rotating stall cells and demonstrate the physics behind their formation, as well as their effect on compressor efficiency. The study also characterizes the entropy generation within the impeller under different operating conditions. While at 77 g/s, the entropy generation is mostly concentrated near the shroud of the impeller with the core flow being almost isentropic, at 30 g/s, there is a significant increase in the area within the blade passage that shows elevated entropy production. The tip leakage flow, its interaction with the blades and the core forward flow, and the reverse flow within the impeller are found to be the major sources of irreversibilities.
Citation: Fluids
PubDate: 2024-07-17
DOI: 10.3390/fluids9070162
Issue No: Vol. 9, No. 7 (2024)
- Fluids, Vol. 9, Pages 163: Air Flow Monitoring in a Bubble Column Using
Ultrasonic Spectrometry
Authors: Ediguer Enrique Franco, Sebastián Henao Santa, John Jairo Cabrera, Santiago Laín
First page: 163
Abstract: This work demonstrates the use of an ultrasonic methodology to monitor bubble density in a water column. A flow regime with droplet size distribution between 0.2 and 2 mm was studied. This range is of particular interest because it frequently appears in industrial flows. Ultrasound is typically used when the size of the bubbles is much larger than the wavelength (low frequency limit). In this study, the radius of the bubbles ranges between 0.6 and 6.8 times the wavelength, where wave propagation becomes a complex phenomenon, making existing analytical methods difficult to apply. Measurements in transmission–reception mode with ultrasonic transducers operating at frequencies of 2.25 and 5.0 MHz were carried out for different superficial velocities. The results showed that a time-averaging scheme is necessary and that wave parameters such as propagation velocity and the slope of the phase spectrum are related to the number of bubbles in the column. The proposed methodology has the potential for application in industrial environments.
Citation: Fluids
PubDate: 2024-07-18
DOI: 10.3390/fluids9070163
Issue No: Vol. 9, No. 7 (2024)
- Fluids, Vol. 9, Pages 164: A Numerical Approach and Study of the
Shock-Wave Structure of Supersonic Jet Flow in a Nozzle
Authors: Andrey Kozelkov, Andrey Struchkov, Aleksandr Kornev, Andrey Kurkin
First page: 164
Abstract: Creating a high-quality aircraft engine is closely connected to the problem of obtaining the jet flow characteristics that appear while an aircraft’s engine is in operation. As natural experiments are costly, studying turbulent jets by numerical simulation appears practical and acute. Biconic nozzle supersonic jet flow is the research subject of this article. A compression and expansion train of waves called barrels were formed in the jet flow at preset conditions. The simulation was performed on an unstructured numerical grid. In order to enhance the calculation accuracy in the shock-wave domain, a hybrid gradient computation scheme and numerical grid static adaptation method were applied in the regions of gas-dynamic values’ significant differential. This approach resulted in a description of nozzle supersonic gas flow structure. It was shown that building local refinement when using a static adaptation numerical grid contributed to improving the accuracy of determining shock waves’ fronts. In addition, this approach facilitated the identification of the Mach disk in the flow when using an unstructured grid, allowing for calculation schemes not higher than a second-order of accuracy.
Citation: Fluids
PubDate: 2024-07-18
DOI: 10.3390/fluids9070164
Issue No: Vol. 9, No. 7 (2024)
- Fluids, Vol. 9, Pages 165: Analytical and Computational Modeling of
Relaxation Times for Non-Newtonian Fluids
Authors: Sheldon Wang, Dalong Gao, Alexandria Wester, Kalyb Beaver, Kuwin Wyke
First page: 165
Abstract: With the availability of efficient and sophisticated finite element analysis (FEA) and computational fluid dynamics (CFD) tools, engineering designs are becoming more software-driven and simulation-based. However, the insights relevant to engineering designs tend to be hidden within massive temporal and spatial data produced with full-fledged three-dimensional simulations. In this paper, we present a preliminary study of the controlled intermittent dispensing of a typical non-Newtonian glue employed in the manufacturing of electric vehicles (EVs). The focus of the study is on the scaling issues derived from different computational and analytical models of interest and importance to the precision control of this non-Newtonian fluid, the lowest dynamic viscosity of which at extremely high shear rates is nearly four million times that of water. More specifically, the abrupt change of the inlet pressure with a constant outlet or ambient pressure and various modeling strategies for transient viscous internal flow with both Newtonian and non-Newtonian fluids are modeled and compared. The analytical and computational results of the developing Newtonian fluid, i.e., water, are derived and computed for validation and verification purposes before the actual applications to the developing non-Newtonian fluid. The concept of a well-established relaxation time before the onset of the steady solution for Newtonian fluids has been validated with both analytical and computational approaches before its expansion and adoption to non-Newtonian fluids with complex rheological behaviors. Other issues attributed to transient operations and precision controls of non-Newtonian fluid delivery involve the pressure pulse and pressure wave propagation within the flexible pipe with compressible or almost incompressible non-Newtonian fluids with a constant pressure at the outlet and a constant mass flow rate or average axial velocity at the inlet, which will be addressed in a separate paper.
Citation: Fluids
PubDate: 2024-07-20
DOI: 10.3390/fluids9070165
Issue No: Vol. 9, No. 7 (2024)
- Fluids, Vol. 9, Pages 166: Visualization and Quantification of Facemask
Leakage Flows and Interpersonal Transmission with Varying Face Coverings
Authors: Xiuhua Si, Jensen S. Xi, Mohamed Talaat, Jay Hoon Park, Ramaswamy Nagarajan, Michael Rein, Jinxiang Xi
First page: 166
Abstract: Although mask-wearing is now widespread, the knowledge of how to quantify or improve their performance remains surprisingly limited and is largely based on empirical evidence. The objective of this study was to visualize the expiratory airflows from facemasks and evaluate aerosol transmission between two persons. Different visualization methods were explored, including the Schlieren optical system, laser/LED-particle imaging system, thermal camera, and vapor–SarGel system. The leakage flows and escaped aerosols were quantified using a hotwire anemometer and a particle counter, respectively. The results show that mask-wearing reduces the exhaled flow velocity from 2~4 m/s (with no facemask) to around 0.1 m/s, thus decreasing droplet transmission speeds. Cloth, surgical, and KN95 masks showed varying leakage flows at the nose top, sides, and chin. The leakage rate also differed between inhalation and exhalation. The neck gaiter has low filtration efficiency and high leakage fractions, providing low protection efficiency. There was considerable deposition in the mouth–nose area, as well as the neck, chin, and jaw, which heightened the risk of self-inoculation through spontaneous face-touching. A face shield plus surgical mask greatly reduced droplets on the head, neck, and face, indicating that double face coverings can be highly effective when a single mask is insufficient. The vapor–SarGel system provided a practical approach to study interpersonal transmission under varying close contact scenarios or with different face coverings.
Citation: Fluids
PubDate: 2024-07-22
DOI: 10.3390/fluids9070166
Issue No: Vol. 9, No. 7 (2024)
- Fluids, Vol. 9, Pages 167: Investigation of Convective Heat Transfer and
Stability on a Rotating Disk: A Novel Experimental Method and Thermal
Modeling
Authors: Yusuf Cati, Stefan aus der Wiesche, Mesut Düzgün
First page: 167
Abstract: Experimental and numerical investigations are conducted on a rotating disk from the perspective of convective heat transfer to understand the effect of heating on the stability of flow. A non-invasive approach with a thermal camera is employed to determine local Nusselt numbers for different rotational rates and perturbation parameters, i.e., the strength of the heat transfer. A novel transient temperature data extraction over the disk radius and an evaluation method are developed and applied for the first time for the air on a rotating disk. The evaluation method utilizes the lumped capacitance approach with a constant heat flux input. Nusselt number distributions from this experimental study show that there is a good agreement with the previous experimental correlations and linear stability analysis on the subject. A significant result of this approach is that by using the experimental setup and developed approach, it is possible to qualitatively show that instability in the flow starts earlier, i.e., an earlier departure from laminar behavior is observed at lower rotational Reynolds numbers with an increasing perturbation parameter, which is due to the strength of heating. Two experimental setups are modeled and simulated using a validated in-house Python code, featuring a three-dimensional thermal model of the disk. The thermal code was developed for the rotating disks and brake disks with a simplified geometry. Experimentally evaluated heat transfer coefficients are implemented and used as convective boundary conditions in the thermal code. Radial temperature distributions are compared with the experimental data, and there is good agreement between the experiment and the model. The model was used to evaluate the effect of radial conduction, which is neglected when using the lumped capacitance approach to determine heat transfer coefficients. It was observed that the radial conduction has a slight effect. The methodology and approach used in this experimental study, combined with the numerical model, can be used for further investigations on the subject.
Citation: Fluids
PubDate: 2024-07-22
DOI: 10.3390/fluids9070167
Issue No: Vol. 9, No. 7 (2024)
- Fluids, Vol. 9, Pages 168: Rim Driven Thruster as Innovative Propulsion
Element for Dual Phase Flows in Plug Flow Reactors
Authors: Maximilian Lackner, Alexander Löhr, Felix Schill, Martin Van Essche
First page: 168
Abstract: The purpose of this work was to test a new setup to pump water with entrained air for application in gas fermentation. A mixed flow, where gas is contained in a liquid to be pumped, rapidly reduces the efficiency of a conventional pump, due to the compressibility of the gas. It is not always possible to degas the fluid, for instance in gas fermentation, which is preferably carried out in tubular reactors (loop fermenters) to achieve a high conversion rate of the gaseous feedstocks. Method: In this work, a rim-driven thruster (RDT) was tested in a lab-scale, cold flow model of a loop reactor with 5–30% (by volume) of gas fraction (air) in the liquid (water) as alternative propulsion element (6 m total pipe length, ambient temperature and pressure). As a result, it was found that the RDT, in connection with a guiding vane providing swirling motion to the two-phase fluid, could pump a mixed flow with up to 25.7% of gas content (by volume) at atmospheric pressure and 25 °C and 0.5 to 2 m/s flow speed. In conclusion, an RDT is advantageous over a classic propulsion element like a centrifugal pump or axial flow pump for transporting liquids with entrained gases. This article describes the potential of rim-driven thrusters, as known from marine propulsion, in biotechnology, the chemical industry, and beyond, to handle multiphase flows.
Citation: Fluids
PubDate: 2024-07-22
DOI: 10.3390/fluids9070168
Issue No: Vol. 9, No. 7 (2024)
- Fluids, Vol. 9, Pages 120: Environmental Hydraulics, Turbulence, and
Sediment Transport, Second Edition
Authors: Jaan H. Pu, Manish Pandey, Prashanth Reddy Hanmaiahgari
First page: 120
Abstract: Within river systems, the process of bed-forming is intricate, dynamic and is shaped by different factors [...]
Citation: Fluids
PubDate: 2024-05-22
DOI: 10.3390/fluids9060120
Issue No: Vol. 9, No. 6 (2024)
- Fluids, Vol. 9, Pages 121: Novel Pour Point Depressants for Crude Oil
Derived from Polyethylene Solution in Hexane and Coal Fly Ash
Authors: Kazim Nadirov, Manap Zhantasov, Tlek Ketegenov, Zhanna Nadirova, Aisulu Batkal, Kaster Kamunur, Gulmira Bimbetova, Rashid Nadirov
First page: 121
Abstract: Oil transportation becomes much more complicated due to the solidification of paraffins in them at low temperatures and the resulting increase in oil viscosity. To solve this problem, special additives as pour point depressants (PPDs) are used to prevent the agglomeration of paraffin crystals. In this work, 15 PPDs were obtained and tested, consisting of a solution of polyethylene in hexane and also, in some cases, from magnetic nanoparticles (MNPs) extracted from coal fly ash. The most effective result was observed with a mixture of 0.25% polyethylene in hexane and 2% MNPs, which managed to lower the oil’s pour point from 18 °C to −17 °C.
Citation: Fluids
PubDate: 2024-05-23
DOI: 10.3390/fluids9060121
Issue No: Vol. 9, No. 6 (2024)
- Fluids, Vol. 9, Pages 122: N-Symmetric Interaction of N Hetons, II:
Analysis of the Case of Arbitrary N
Authors: Konstantin V. Koshel, Mikhail A. Sokolovskiy, David G. Dritschel, Jean N. Reinaud
First page: 122
Abstract: This paper seeks and examines N-symmetric vortical solutions of the two-layer geostrophic model for the special case when the vortices (or eddies) have vanishing summed strength (circulation anomaly). This study is an extension [Sokolovskiy et al. Phys. Fluids 2020, 32, 09660], where the general formulation for arbitrary N was given, but the analysis was only carried out for N=2. Here, families of stationary solutions are obtained and their properties, including asymptotic ones, are investigated in detail. From the point of view of geophysical applications, the results may help interpret the propagation of thermal anomalies in the oceans.
Citation: Fluids
PubDate: 2024-05-24
DOI: 10.3390/fluids9060122
Issue No: Vol. 9, No. 6 (2024)
- Fluids, Vol. 9, Pages 123: Simulation on the Separation of Breast Cancer
Cells within a Dual-Patterned End Microfluidic Device
Authors: Diganta Dutta, Xavier Palmer, Jung Yul Lim, Surabhi Chandra
First page: 123
Abstract: Microfluidic devices have long been useful for both the modeling and diagnostics of numerous diseases. In the past 20 years, they have been increasingly adopted for helping to study those in the family of breast cancer through characterizing breast cancer cells and advancing treatment research in portable and replicable formats. This paper adds to the body of work concerning cancer-focused microfluidics by proposing a simulation of a hypothetical bi-ended three-pronged device with a single channel and 16 electrodes with 8 pairs under different voltage and frequency regimes using COMSOL. Further, a study was conducted to examine the frequencies most effective for ACEO to separate cancer cells and accompanying particles. The study revealed that the frequency of EF has a more significant impact on the separation of particles than the inlet velocity. Inlet velocity variations while holding the frequency of EF constant resulted in a consistent trend showing a direct proportionality between inlet velocity and net velocity. These findings suggest that optimizing the frequency of EF could lead to more effective particle separation and targeted therapeutic interventions for breast cancer. This study hopefully will help to create targeted therapeutic interventions by bridging the disparity between in vitro and in vivo models.
Citation: Fluids
PubDate: 2024-05-25
DOI: 10.3390/fluids9060123
Issue No: Vol. 9, No. 6 (2024)
- Fluids, Vol. 9, Pages 124: Subgrid Turbulent Flux Models for Large Eddy
Simulations of Diffusion Flames in Space Propulsion
Authors: Daniel Martinez-Sanchis, Andrej Sternin, Sagnik Banik, Oskar Haidn, Martin Tajmar
First page: 124
Abstract: Subgrid scale models for unresolved turbulent fluxes are investigated, with a focus on combustion for space propulsion applications. An extension to the gradient model is proposed, introducing a dependency on the local burning regimen. The dynamic behaviors of the model’s coefficients are investigated, and scaling laws are studied. The discussed models are validated using a DNS database of a high-pressure, turbulent, fuel-rich methane–oxygen diffusion flame. The operating point and turbulence characteristics are selected to resemble those of modern combustors for space propulsion applications to support the future usage of the devised model in this context.
Citation: Fluids
PubDate: 2024-05-26
DOI: 10.3390/fluids9060124
Issue No: Vol. 9, No. 6 (2024)
- Fluids, Vol. 9, Pages 125: Effects of Partial Premixing and Coflow
Temperature on Flame Stabilization of Lifted Jet Flames of Dimethyl Ether
in a Vitiated Coflow Based on Stochastic Multiple Mapping Conditioning
Approach
Authors: Sanjeev Kumar Ghai, Rajat Gupta, Santanu De
First page: 125
Abstract: The Reynolds-averaged Navier–Stokes (RANS)-based stochastic multiple mapping conditioning (MMC) approach has been used to study partially premixed jet flames of dimethyl ether (DME) introduced into a vitiated coflowing oxidizer stream. This study investigates DME flames with varying degrees of partial premixing within a fuel jet across different coflow temperatures, delving into the underlying flame structure and stabilization mechanisms. Employing a turbulence k-ε model with a customized set of constants, the MMC technique utilizes a mixture fraction as the primary scalar, mapped to the reference variable. Solving a set of ordinary differential equations for the evolution of Lagrangian stochastic particles’ position and composition, the molecular mixing of these particles is executed using the modified Curl’s model. The lift-off height (LOH) derived from RANS-MMC simulations are juxtaposed with experimental data for different degrees of partial premixing of fuel jets and various coflow temperatures. The RANS-MMC methodology adeptly captures LOH for pure DME jets but exhibits an underestimation of flame LOH for partially premixed jet scenarios. Notably, as the degree of premixing escalates, a conspicuous underprediction in LOH becomes apparent. Conditional scatter and contour plots of OH and CH2O unveil that the propagation of partially premixed flames emerges as the dominant mechanism at high coflow temperatures, while autoignition governs flame stabilization at lower coflow temperatures in partially premixed flames. Additionally, for pure DME flames, autoignition remains the primary flame stabilization mechanism across all coflow temperature conditions. The study underscores the importance of considering the degree of premixing in partially premixed jet flames, as it significantly impacts flame stabilization mechanisms and LOH, thereby providing crucial insights into combustion dynamics for various practical applications.
Citation: Fluids
PubDate: 2024-05-26
DOI: 10.3390/fluids9060125
Issue No: Vol. 9, No. 6 (2024)
- Fluids, Vol. 9, Pages 126: Statistical Analysis of Bubble Parameters from
a Model Bubble Column with and without Counter-Current Flow
Authors: P. Kováts, K. Zähringer
First page: 126
Abstract: Bubble columns are widely used in numerous industrial processes because of their advantages in operation, design, and maintenance compared to other multiphase reactor types. In contrast to their simple design, the generated flow conditions inside a bubble column reactor are quite complex, especially in continuous mode with counter-current liquid flow. For the design and optimization of such reactors, precise numerical simulations and modelling are needed. These simulations and models have to be validated with experimental data. For this reason, experiments were carried out in a laboratory-scale bubble column using shadow imaging and particle image velocimetry (PIV) techniques with and without counter-current liquid flow. In the experiments, two types of gases—relatively poorly soluble air and well-soluble CO2—were used and the bubbles were generated with three different capillary diameters. With changing gas and liquid flow rates, overall, 108 different flow conditions were investigated. In addition to the liquid flow fields captured by PIV, shadow imaging data were also statistically evaluated in the measurement volume and bubble parameters such as bubble diameter, velocity, aspect ratio, bubble motion direction, and inclination. The bubble slip velocity was calculated from the measured liquid and bubble velocities. The analysis of these parameters shows that the counter-current liquid flow has a noticeable influence on the bubble parameters, especially on the bubble velocity and motion direction. In the case of CO2 bubbles, remarkable bubble shrinkage was observed with counter-current liquid flow due to the enhanced mass transfer. The results obtained for bubble aspect ratio are compared to known correlations from the literature. The comprehensive and extensive bubble data obtained in this study will now be used as a source for the development of correlations needed in the validation of numerical simulations and models. The data are available from the authors on request.
Citation: Fluids
PubDate: 2024-05-28
DOI: 10.3390/fluids9060126
Issue No: Vol. 9, No. 6 (2024)
- Fluids, Vol. 9, Pages 127: Numerical Dissipation Control in High-Order
Methods for Compressible Turbulence: Recent Development
Authors: H. C. Yee, Björn Sjögreen
First page: 127
Abstract: This comprehensive overview presents our continued efforts in high-order finite difference method (FDM) development for adaptive numerical dissipation control in the long-time integration of direct numerical simulation (DNS), large eddy simulation (LES), and implicit LES (ILES) computations of compressible turbulence for gas dynamics and MHD. The focus is on turbulence with shock wave numerical simulations using the adaptive blending of high-order structure-preserving non-dissipative methods (classical central, Padé (compact), and dispersion relation-preserving (DRP)) with high-order shock-capturing methods in such a way that high-order shock-capturing methods are active only in the vicinity of shock/shear waves, and high-gradient and spurious high-frequency oscillation regions guided via flow sensors. Any efficient and high-resolution high-order shock-capturing methods are good candidates for the blending of methods procedure. Typically, the adaptive blending of more than one method falls under two camps: hybrid methods and nonlinear filter methods. They are applicable to unstructured finite volume, finite element, discontinuous Galerkin, and spectral element methods. This work represents the culmination of over 20 years of high-order FDM developments and hands-on experience by the authors and collaborators in adaptive numerical dissipation control using the “high order nonlinear filter approach”. Extensions of these FDM versions to curvilinear nonuniform, freestream-preserving moving grids and time-varying deforming grids were also developed. By examining the construction of these two approaches using the high-order multistage type of temporal discretization, the nonlinear filter approach is made more efficient and less CPU-intensive while obtaining similar accuracy. A representative variety of test cases that compare the various blending of high-order methods with standalone standard methods is illustrated. Due to the fact that our nonlinear filter methods are not well known in compressible turbulence with shock waves, the intent of this comprehensive overview is for general audiences who are not familiar with our nonlinear filter methods. For readers interested in the implementation of our methods into their computer code, it is hoped that the long overview will be helpful.
Citation: Fluids
PubDate: 2024-05-29
DOI: 10.3390/fluids9060127
Issue No: Vol. 9, No. 6 (2024)
- Fluids, Vol. 9, Pages 128: Measuring Turbulent Flows: Analyzing a
Stochastic Process with Stochastic Tools
Authors: Evangelos Rozos, Jörg Wieland, Jorge Leandro
First page: 128
Abstract: Assessing drag force and Reynolds stresses in turbulent flows is crucial for evaluating the stability and longevity of hydraulic structures. Yet, this task is challenging due to the complex nature of turbulent flows. To address this, physical models are often employed. Nonetheless, this practice is associated with difficulties, especially in the case of high sampling frequency where the inherent randomness of velocity fluctuations becomes mixed with the measurement noise. This study introduces a stochastic approach, which aims to mitigate bias from measurement errors and provide a probabilistic estimate of extreme stress values. To accomplish this, a simple experimental setup with a hydraulic jump was employed to acquire long-duration velocity measurements. Subsequently, a modified first-order autoregressive model was applied through ensemble simulations, demonstrating the benefits of the stochastic approach. The analysis highlights its effectiveness in estimating the uncertainty of extreme events frequency and minimizing the bias induced by the noise in the high-magnitude velocity measurements and by the limited length of observations. These findings contribute to advancing our understanding of turbulent flow analysis and have implications for the design and assessment of hydraulic structures.
Citation: Fluids
PubDate: 2024-05-30
DOI: 10.3390/fluids9060128
Issue No: Vol. 9, No. 6 (2024)
- Fluids, Vol. 9, Pages 129: Hartmann Flow of Two-Layered Fluids in
Horizontal and Inclined Channels
Authors: Arseniy Parfenov, Alexander Gelfgat, Amos Ullmann, Neima Brauner
First page: 129
Abstract: The effect of a transverse magnetic field on two-phase stratified flow in horizontal and inclined channels is studied. The lower heavier phase is assumed to be an electrical conductor (e.g., liquid metal), while the upper lighter phase is fully dielectric (e.g., gas). The flow is defined by prescribed flow rates in each phase, so the unknown frictional pressure gradient and location of the interface separating the phases (holdup) are found as part of the whole solution. It is shown that the solution of such a two-phase Hartmann flow is determined by four dimensionless parameters: the phases’ viscosity and flow-rate ratios, the inclination parameter, and the Hartmann number. The changes in velocity profiles, holdups, and pressure gradients with variations in the magnetic field and the phases’ flow-rate ratio are reported. The potential lubrication effect of the gas layer and pumping power reduction are found to be limited to low magnetic field strength. The effect of the magnetic field strength on the possibility of obtaining countercurrent flow and multiple flow states in concurrent upward and downward flows, and the associated flow characteristics, such as velocity profiles, back-flow phenomena, and pressure gradient, are explored. It is shown that increasing the magnetic field strength reduces the flow-rate range for which multiple solutions are obtained in concurrent flows and the flow-rate range where countercurrent flow is feasible.
Citation: Fluids
PubDate: 2024-05-30
DOI: 10.3390/fluids9060129
Issue No: Vol. 9, No. 6 (2024)
- Fluids, Vol. 9, Pages 130: Improving the Energy Efficiency of Vehicles by
Ensuring the Optimal Value of Excess Pressure in the Cabin Depending on
the Travel Speed
Authors: Ivan Panfilov, Alexey N. Beskopylny, Besarion Meskhi
First page: 130
Abstract: This work is devoted to the study of gas-dynamic processes in the operation of climate control systems in the cabins of vehicles (HVAC), focusing on pressure values. This research examines the issue of assessing the required values of air overpressure inside the locomotive cabin, which is necessary to prevent gas exchange between the interior of the cabin and the outside air through leaks in the cabin, including protection against the penetration of harmful substances. The pressure boost in the cabin depends, among other things, on the external air pressure on the locomotive body, the power of the climate system fan, and the ratio of the input and output deflectors. To determine the external air pressure, the problem of train movement in a wind tunnel is considered, the internal and external fluids domain is considered, and the air pressure on the cabin skin is determined using numerical methods CFD based on the Navier–Stokes equations, depending on the speed of movement. The finite-volume modeling package Ansys CFD (Fluent) was used as an implementation. The values of excess internal pressure, which ensures the operation of the climate system under different operating modes, were studied numerically and on the basis of an approximate applied formula. In particular, studies were carried out depending on the speed and movement of transport, on the airflow of the climate system, and on the ratio of the areas of input and output parameters. During a numerical experiment, it was found that for a train speed of 100 km/h, the required excess pressure is 560 kPa, and the most energy-efficient way to increase pressure is to regulate the area of the outlet valves.
Citation: Fluids
PubDate: 2024-05-31
DOI: 10.3390/fluids9060130
Issue No: Vol. 9, No. 6 (2024)
- Fluids, Vol. 9, Pages 131: Passive Control of Vortices in the Wake of a
Bluff Body
Authors: Marek Pátý, Michael Valášek, Emanuele Resta, Roberto Marsilio, Michele Ferlauto
First page: 131
Abstract: Vortices belong to the most important phenomena in fluid dynamics and play an essential role in many engineering applications. They can act detrimentally by harnessing the flow energy and reducing the efficiency of an aerodynamic device, whereas in other cases, their presence can be exploited to achieve targeted flow conditions. The control of the vortex parameters is desirable in both cases. In this paper, we introduce an optimization strategy for the control of vortices in the wake of a bluff body. Flow modelling is based on RANS and DES computations, validated by experimental data. The algorithm for vortex identification and characterization is based on the triple decomposition of motion. It produces a quantitative measure of vortex strength which is used to define the objective function in the optimization procedure. It is shown how the shape of an aerodynamic device can be altered to achieve the desired characteristics of vortices in its wake. The studied case is closely related to flame holders for combustion applications, but the conceptual approach has a general applicability to vortex control.
Citation: Fluids
PubDate: 2024-05-31
DOI: 10.3390/fluids9060131
Issue No: Vol. 9, No. 6 (2024)
- Fluids, Vol. 9, Pages 132: Gas–Liquid Mass Transfer Intensification
for Selective Alkyne Semi-Hydrogenation with an Advanced Elastic Catalytic
Foam-Bed Reactor
Authors: Mohamad Fayad, Maïté Michaud, Han Peng, Vincent Ritleng, David Edouard
First page: 132
Abstract: The Elastic Catalytic Foam-bed Reactor (EcFR) technology was used to enhance a model catalytic hydrogenation reaction by improving gas–liquid mass transfer. This advanced technology is based on a column packed with a commercial elastomeric polyurethane open-cell foam, which also acts as a catalyst support. A simple and efficient crankshaft-inspired system applied in situ compression/relaxation movements to the foam bed. For the first time, the catalytic support parameters (i.e., porosity, tortuosity, characteristic length, etc.) underwent cyclic and controlled changes over time. These dynamic cycles have made it possible to intensify the transfer of gas to liquid at a constant energy level. The application chosen was the selective hydrogenation of phenylacetylene to styrene in an alcoholic solution using a palladium-based catalyst under hydrogen bubble conditions. The conversion observed with this EcFR at 1 Hz as cycle frequency was compared with that observed with a conventional Fixed Catalytic Foam-bed Reactor (FcFR).
Citation: Fluids
PubDate: 2024-06-01
DOI: 10.3390/fluids9060132
Issue No: Vol. 9, No. 6 (2024)
- Fluids, Vol. 9, Pages 133: Convergence towards High-Speed Steady States
Using High-Order Accurate Shock-Capturing Schemes
Authors: Juan C. Assis, Ricardo D. Santos, Mateus S. Schuabb, Carlos E. G. Falcão, Rômulo B. Freitas, Leonardo S. de B. Alves
First page: 133
Abstract: Creating time-marching unsteady governing equations for a steady state in high-speed flows is not a trivial task. Residue convergence in time cannot be achieved when using most low- and high-order spatial discretization schemes. Recently, high-order, weighted, essentially non-oscillatory schemes have been specially designed for steady-state simulations. They have been shown to be capable of achieving machine precision residues when simulating the Euler equations under canonical coordinates. In the present work, we review these schemes and show that they can also achieve machine residues when simulating the Navier–Stokes equations under generalized coordinates. This is carried out by considering three supersonic flows of perfect fluids, namely the flow upstream a cylinder, the flow over a blunt wedge, and the flow over a compression ramp.
Citation: Fluids
PubDate: 2024-06-01
DOI: 10.3390/fluids9060133
Issue No: Vol. 9, No. 6 (2024)
- Fluids, Vol. 9, Pages 134: AI-Based Detection of Surge and Rotating Stall
in Axial Compressors via Dynamic Model Parameter Estimation
Authors: Sara Zanotti, Davide Ceschini, Michele Ferlauto
First page: 134
Abstract: Compressors are an essential component of aircraft engines. Their design and operation must be extremely reliable as engine safety and performance depend greatly on these elements. Axial compressors exhibit instabilities, such as surge or rotating stall, in a region close to the peak of their performance curves. These fluid dynamic instabilities can cause drops in efficiency, stress on the blades, fatigue, and even failures. Compressors are handled therefore by operating with a safety margin far from the surge line. Moreover, models able to predict onset instabilities and to reproduce them are of great interest. A dynamic system able to describe successfully both surge and rotating stall is the model presented by Moore and Greitzer That model has also been used for developing control laws of the compressor dynamics. The present work aims at developing an artificial neural network (ANN) approach able to predict either the permanence of the system in stable working condition or the onset instabilities from a time sequence of the compressor dynamics. Different solutions were tried to find the most suitable model for identifying the system, as well as the effects of the duration of the time sequence on the accuracy of the predicted compressor working conditions. The network was further tried for sequences with different initial values in order to perform a system analysis that included multiple variations from the initial database. The results show how it is possible to identify with high accuracy both rotating stall and surge with the ANN approach. Moreover, the presence of an underlying fluid dynamic model shares some similarities with physically informed AI procedures.
Citation: Fluids
PubDate: 2024-06-01
DOI: 10.3390/fluids9060134
Issue No: Vol. 9, No. 6 (2024)
- Fluids, Vol. 9, Pages 135: Laminar Boundary Layer over a Serrated
Backward-Facing Step
Authors: Real J. KC, Trevor C. Wilson, Nicholas A. Lucido, Aaron S. Alexander, Jamey D. Jacob, Brian R. Elbing
First page: 135
Abstract: Laminar flow over a modified backward-facing step (BFS) was studied experimentally and computationally, with the results compared to a flight test on a Piper Cherokee wing. The BFS was modified with a serrated spanwise variation while maintaining a constant step height, and this modification is termed a serrated BFS (sBFS). A scaling law was proposed and then used to develop the experimental operation conditions. The experiments showed evidence that the transition to turbulence was delayed over the forward part of the serration (termed the valley). The boundary layer growth and characterization were used to validate the computational model, which was then used to examine details not available from the experiment, including the wall shear stress distribution and streamlines as they go over the sBFS. The wall shear stress showed the formation of low-shear diamonds downstream of the sBFS valley that were associated with laminar flow, which confirmed previous assumptions about the low-shear diamonds observed in the flight tests. The length of the low-shear diamonds was scaled with the sBFS geometry. Finally, the streamlines showed that the near-wall flow forward of the sBFS is pumped towards the sBFS peak, where it rapidly transitions to turbulence at that location.
Citation: Fluids
PubDate: 2024-06-02
DOI: 10.3390/fluids9060135
Issue No: Vol. 9, No. 6 (2024)
- Fluids, Vol. 9, Pages 136: Pump System Model Parameter Identification
Based on Experimental and Simulation Data
Authors: Sheldon Wang, Dalong Gao, Alexandria Wester, Kalyb Beaver, Shanae Edwards, Carrie Anne Taylor
First page: 136
Abstract: In this paper, the entire downhole fluid-sucker rod-pump system is replaced with a viscoelastic vibration model, namely a third-order differential equation with an inhomogeneous forcing term. Both Kelvin’s and Maxwell’s viscoelastic models can be implemented along with the dynamic behaviors of a mass point attached to the viscoelastic model. By employing the time-dependent polished rod force measured with a dynamometer as the input to the viscoelastic dynamic model, we have obtained the displacement responses, which match closely with the experimental measurements in actual operations, through an iterative process. The key discovery of this work is the feasibility of the so-called inverse optimization procedure, which can be utilized to identify the equivalent scaling factor and viscoelastic system parameters. The proposed Newton–Raphson iterative method, with some terms in the Jacobian matrix expressed with averaged rates of changes based on perturbations of up to two independent parameters, provides a feasible tool for optimization issues related to complex engineering problems with mere information of input and output data from either experiments or comprehensive simulations. The same inverse optimization procedure is also implemented to model the entire fluid delivery system of a very viscous non-Newtonian polymer modeled as a first-order ordinary differential equation (ODE) system similar to the transient entrance developing flow. The convergent parameter reproduces transient solutions that match very well with those from fully fledged computational fluid dynamics models with the required inlet volume flow rate and outlet pressure conditions.
Citation: Fluids
PubDate: 2024-06-04
DOI: 10.3390/fluids9060136
Issue No: Vol. 9, No. 6 (2024)
- Fluids, Vol. 9, Pages 137: Advanced RBF Methods for Mapping Aerodynamic
Loads onto Structures in High-Fidelity FSI Simulations
Authors: Andrea Chiappa, Andrea Lopez, Corrado Groth
First page: 137
Abstract: The reliable exchange of data is a crucial issue for the loose coupling of computational fluid dynamics (CFD) and computational structural mechanics (CSM) modules in fluid–structure interaction (FSI) applications. This paper presents a comparison between two methods for mapping the traction field across mismatching grids, namely the RIBES method and the preCICE algorithm, both based on radial basis function (RBF) interpolation. The two methods demonstrate different degrees of control over balance preservation during mapping, with the RIBES algorithm exhibiting greater efficacy. Test benches are a parametric double curved geometry and a wind tunnel mock-up. In this second case, forces from mapping are used to load a CSM model to retrieve stress and displacement fields. Differences in FEM results are appreciable although not significant, showing a correlation between the accuracy of balance preservation during data mapping and the structural output.
Citation: Fluids
PubDate: 2024-06-06
DOI: 10.3390/fluids9060137
Issue No: Vol. 9, No. 6 (2024)
- Fluids, Vol. 9, Pages 138: Correction Factors for the Use of 1D Solution
Methods for Dynamic Laminar Liquid Flow through Curved Tubes
Authors: Travis Wiens
First page: 138
Abstract: The modeling of transient flows of liquids through tubes is required for studies in water hammer, switched inertance hydraulic converters, and noise reduction in hydraulic equipment. While 3D gridded computational fluid dynamics (CFD) methods exist for the prediction of dynamic flows and pressures in these applications, they are computationally costly, and it is more common to use 1D methods such as the method of characteristics (MOC), transmission line method (TLM), or frequency domain methods. These 1D methods give good approximations of results but require many orders of magnitude less computation time. While these tubes are typically curved or coiled in practical applications, existing 1D solution methods assume straight tubes, often with unknown deviation from the curved tube solution. This paper uses CFD simulations to determine the correction factors that can be used for existing 1D methods with curved tubes. The paper also presents information that can be used to help evaluate the expected errors resulting from this approximation.
Citation: Fluids
PubDate: 2024-06-06
DOI: 10.3390/fluids9060138
Issue No: Vol. 9, No. 6 (2024)
- Fluids, Vol. 9, Pages 139: Stochastic Equations of Hydrodynamic Theory of
Plasma
Authors: Artur V. Dmitrenko
First page: 139
Abstract: Stochastic equations of the hydrodynamic theory of plasma are presented in relation to strong external fields. It is shown that the use of these stochastic equations makes it possible to obtain new theoretical solutions for plasma as a result of its heating in a strong external electric field. Theoretical solutions for the conductivity of turbulent plasma when heated in an external electric field of 100 V/cm are considered. Calculated values for the electron drift velocity, electron mobility, electron collision frequency, and the Coulomb logarithm in the region of strong electric fields are obtained. Here we consider experiments on turbulent heating of hydrogen plasma in the range of electric field strength of 100 < E < 1000. The calculated dependences of plasma conductivity are in satisfactory agreement with experimental data for heating plasma in a strong electric field. It is shown that the plasma turbulence in the region of strong electric fields E ~1000 V/cm is close to 100%. For the first time, it is confirmed that the derived dependences for collision frequency, drift velocity, and other values include the degree of turbulence of plasma, which makes it possible to correctly describe experimental data for heating plasma even with strong electric fields. In addition, it was determined that the scatter of experimental data may be associated with the variability of the function in the expression for the heat flux density. For the first time, it is shown theoretically that the experimentally determined fact of the possibility of the existence of an approximate constancy of plasma conductivity in the region E = 100–1000 V/cm can occur with an error of ~30%. The results show significant advantages of the stochastic hydrodynamic plasma theory over other methods that are not yet able to satisfactorily as well as qualitatively and quantitatively predict long-known experimental data while taking into account the degree of turbulence.
Citation: Fluids
PubDate: 2024-06-07
DOI: 10.3390/fluids9060139
Issue No: Vol. 9, No. 6 (2024)
- Fluids, Vol. 9, Pages 140: Analytical Solution for Transient
Electroosmotic and Pressure-Driven Flows in Microtubes
Authors: Yu Feng, Hang Yi, Ruguan Liu
First page: 140
Abstract: This study focuses on deriving and presenting an infinite series as the analytical solution for transient electroosmotic and pressure-driven flows in microtubes. Such a mathematical presentation of fluid dynamics under simultaneous electric field and pressure gradients leverages governing equations derived from the generalized continuity and momentum equations simplified for laminar and axisymmetric flow. Velocity profile developments, apparent slip-induced flow rates, and shear stress distributions were analyzed by varying values of the ratio of microtube radius to Debye length and the electroosmotic slip velocity. Additionally, the “retarded time” in terms of hydraulic diameter, kinematic viscosity, and slip-induced flow rate was derived. A simpler polynomial series approximation for steady electroosmotic flow is also proposed for engineering convenience. The analytical solutions obtained in this study not only enhance the fundamental understanding of the electroosmotic flow characteristics within microtubes, emphasizing the interplay between electroosmotic and pressure-driven mechanisms, but also serve as a benchmark for validating computational fluid dynamics models for electroosmotic flow simulations in more complex flow domains. Moreover, the analytical approach aids in the parametric analysis, providing deeper insights into the impact of physical parameters on electroosmotic and pressure-driven flow behavior, which is critical for optimizing device performance in practical applications. These findings also offer insightful implications for diagnostic and therapeutic strategies in healthcare, particularly enhancing the capabilities of lab-on-a-chip technologies and paving the way for future research in the development and optimization of microfluidic systems.
Citation: Fluids
PubDate: 2024-06-11
DOI: 10.3390/fluids9060140
Issue No: Vol. 9, No. 6 (2024)
- Fluids, Vol. 9, Pages 141: Valveless Pumping with an Unsteady Stenosis in
an Open Tank Configuration
Authors: Christos Manopoulos, Dimitrios Mathioulakis
First page: 141
Abstract: This work examines the beneficial role of an unsteady stenosis, not driven by any external energy source, as a means for augmenting the flow rate of a valveless pump in a hydraulic loop, including an open tank. In contrast to our previous work, in which the concept of the latter stenosis was introduced for the first time in a horizontal closed loop, here, gravity was taken into account. The stenosis neck cross-sectional area was controlled by the fluid pressure and the opposing force applied externally by a spring of adjustable tension. A pincher compressed and decompressed a part of the pump’s flexible tube periodically, with frequencies from 5 Hz to 11 Hz and compression ratios Ab from 24% to 65%. The presence of the stenosis increased the net flow rate by 19 times for Ab = 24% and 6.3 times for Ab = 38%; whereas for Ab = 65%, the flow rates were comparable. The volumetric efficiency varied from 30% to 40% under the presence of the stenosis, and from 2% to 20% without the stenosis. The role of the stenosis was to cause a unidirectional flow, opening during tube compression and closing during decompression. The pressure amplitudes along the flexible tube increased towards the rigid–flexible tube junction (as a result of the wave reflections), which were found to be significantly attenuated by the presence of the stenosis, whereas the flow rate pulsations did not exceed 10% of the mean at the peak net flow rates.
Citation: Fluids
PubDate: 2024-06-12
DOI: 10.3390/fluids9060141
Issue No: Vol. 9, No. 6 (2024)
- Fluids, Vol. 9, Pages 142: Interrupter Technique Revisited: Building an
Experimental Mechanical Ventilator to Assess Respiratory Mechanics in
Large Animals
Authors: Camilla Zilianti, Erfan Bashar, Anna Kyriakoudi, Matteo Pecchiari
First page: 142
Abstract: Large animals are increasingly used as experimental models of respiratory diseases. Precise characterization of respiratory mechanics requires dedicated equipment with specific characteristics which are difficult to find together in the same commercial device. In this work, we describe building and validation of a computer-controlled ventilator able to perform rapid airways occlusions during constant flow inflations followed by a prolonged inspiratory hold. A constant airflow is provided by a high pressure source (5 atm) connected to the breathing circuit by three proportional valves. The combined action of three 2-way valves produces the phases of the breath. During non-inspiratory breath phases, airflow is diverted to a flowmeter for precise feedback regulation of the proportional valves. A computer interface enables the user to change the breathing pattern, trigger test breaths or run predetermined breaths sequences. A respiratory system model was used to test the ability of the ventilator to correctly estimate interrupter resistance. The ventilator was able to produce a wide range of constant flows (0.1–1.6 L/s) with the selected timing. Errors in the measurement of interrupter resistance were small (1 ± 5% of the reference value). The device described reliably estimated interrupter resistance and can be useful as a measuring tool in large animal research.
Citation: Fluids
PubDate: 2024-06-14
DOI: 10.3390/fluids9060142
Issue No: Vol. 9, No. 6 (2024)
- Fluids, Vol. 9, Pages 143: Three-Dimensional Long-Wave Instability of an
Evaporation/Condensation Film
Authors: Weiyang Jiang, Ruiqi Huang, Qiang Yang, Zijing Ding
First page: 143
Abstract: This paper explores the stability and dynamics of a three-dimensional evaporating/condensing film while falling down a heated/cooled incline. Instead of using the Hertz–Knudsen–Langmuir relation, a more comprehensive phase-change boundary condition is employed. A nonlinear differential equation is derived based on the Benny-type equation, which takes into account gravity, energy transport, vapor recoil, effective pressure, and evaporation. The impact of effective pressure and vapor recoil on instability is studied using a linear stability analysis. The results show that spanwise perturbations can amplify the destabilizing effects of vapor recoil, leading to instability. Energy transport along the interface has almost no effect on the stability of the system, but it does influence the linear wave speed. Nonlinear evolution demonstrates that, in contrast to the vapor recoil effect, effective pressure can improve stability and delay film rupture. The self-similar solution demonstrates that the minimal film thickness decreases as (tr−t)1/2 and (tr−t)1/3 under the dominance of evaporation and vapor recoil, respectively.
Citation: Fluids
PubDate: 2024-06-14
DOI: 10.3390/fluids9060143
Issue No: Vol. 9, No. 6 (2024)
- Fluids, Vol. 9, Pages 144: Toward Scale-Adaptive Subgrid-Scale Model in
LES for Turbulent Flow Past a Sphere
Authors: H. Ali Marefat, Jahrul M Alam, Kevin Pope
First page: 144
Abstract: This study explores the dynamics of turbulent flow around a sphere at a Reynolds number of Re=103 using large-eddy simulation, focusing on the intricate connection between vortices and strain within the recirculation bubble of the wake. Employing a relatively new subgrid-scale modeling approach based on scale adaptivity, this research implements a functional relation to compute ksgs that encompasses both vortex-stretching and strain rate mechanisms essential for the energy cascade process. The effectiveness of this approach is analyzed in the wake of the sphere, particularly in the recirculation bubble, at the specified Reynolds number. It is also evaluated in comparison with two different subgrid-scale models through detailed analysis of the coherent structures within the recirculation bubble. These models—scale-adaptive, k-Equation, and dynamic k-Equation—are assessed for their ability to capture the complex flow dynamics near the wake. The findings indicate that while all models proficiently simulate key turbulent wake features such as vortex formation and kinetic energy distribution, they exhibit unique strengths and limitations in depicting specific flow characteristics. The scale-adaptive model shows a good ability to dynamically adjust to local flow conditions, thereby enhancing the representation of turbulent structures and eddy viscosity. Similarly, the dKE model exhibits advantages in energy dissipation and vortex dynamics due to its capability to adjust coefficients dynamically based on local conditions. The comparative analysis and statistical evaluation of vortex stretching and strain across models deepen the understanding of turbulence asymmetries and intensities, providing crucial insights for advancing aerodynamic design and analysis in various engineering fields and laying the groundwork for further sophisticated turbulence modeling explorations.
Citation: Fluids
PubDate: 2024-06-18
DOI: 10.3390/fluids9060144
Issue No: Vol. 9, No. 6 (2024)
- Fluids, Vol. 9, Pages 145: Analysis of the Heat Concentration Phenomenon
on the Turbine (TBN) Building of a Coal-Fired Power Plant and Suggestions
for Improvement
Authors: Mok-Lyang Cho, Seon-Bong Lee
First page: 145
Abstract: Coal-fired power plants generate power by rotating turbines (TBNs). According to the high-temperature work exposure standard (KOSHA CODE 02), the turbine (TBN) building, where essential power-generation components, turbines (TBNs), are installed, contains various types of high-temperature equipment, creating a hazardous working environment for onsite employees. In addition, malfunctions from lubricant leaks occur at the moving parts of such power-generation equipment in the building, due to the high-temperature environment. In this study, we analyzed the heat concentration phenomenon in the turbine (TBN) building using computational fluid dynamics (CFD) software and made recommendations for its improvement. We examined options for installing automatic ventilation windows and additional heat exhaust fans on turbine (TBN) floors. We discovered that installing an automatic ventilation window and a heat exhaust fan on the deaerator floor can reduce the average temperature by 1.2 °C and 6.6 °C, respectively. In addition, the mezzanine floor, where the core heat-generating equipment is installed, is significantly affected by radiant heat. To mitigate the heat concentration phenomenon, we recommend installing additional radiant heat shields.
Citation: Fluids
PubDate: 2024-06-19
DOI: 10.3390/fluids9060145
Issue No: Vol. 9, No. 6 (2024)
- Fluids, Vol. 9, Pages 146: Experimental Study of Oil–Water Flow
Downstream of a Restriction in a Horizontal Pipe
Authors: Denghong Zhou, Kanat Karatayev, Yilin Fan, Benjamin Straiton, Qussai Marashdeh
First page: 146
Abstract: This work presents an experimental study on oil–water flow downstream of a restriction. The flow pattern, volumetric phase distribution, and their impacts on pressure drop are discussed. We employed two techniques to visualize the oil–water flow patterns, a high-speed camera and an Electrical Capacitance Volume Tomography (ECVT) system. The ECVT system is a non-intrusive device that measures the volumetric phase distribution at the pipe cross-section with time, which plays a critical role in determining the continuous phase in the oil–water flow, and therefore the oil–water flow pattern. In this study, we delved into the oil–water flow pattern and volumetric phase distribution for different valve openings, flow rates, and water cuts, and how they impact the pressure drop. The experimental results have demonstrated a strong relationship between the oil–water flow pattern and the pressure gradient, while the oil–water flow pattern is significantly influenced by the flowing conditions and the valve openings. The impacts of water cuts on the oil–water flow pattern are more obvious for smaller valve openings. For large valve openings, the oil and water phases tend to be more separated. This results in a moderate variation in the pressure gradient as a function of water cuts. However, it becomes more complex as the valve opening decreases. The pressure gradient generally increases with decreasing valve openings until the flow pattern becomes an oil-in-water dispersed flow. The impact of the valve on the pressure gradient is more pronounced in water-dominated flow when the water cut is above the inversion point, while it seems to be most obvious for medium water cut conditions.
Citation: Fluids
PubDate: 2024-06-20
DOI: 10.3390/fluids9060146
Issue No: Vol. 9, No. 6 (2024)
- Fluids, Vol. 9, Pages 100: Liquid-Solid Interaction to Evaluate Thermal
Aging Effects on Carbon Fiber-Reinforced Composites
Authors: Poom Narongdej, Jack Hanson, Ehsan Barjasteh, Sara Moghtadernejad
First page: 100
Abstract: This study investigated the thermally induced aging effects on a carbon fiber-reinforced composite (CFRP) comprising benzoxazine (BZ) and cycloaliphatic epoxy resin (CER). Herein, we employed various testing methodologies to assess the aging behavior of CFRP samples with differing CER and BZ ratios. Traditional techniques, including weight change quantification and qualitative analysis of surface morphology, reveal that higher CER content correlates with increased aging. Additionally, wettability analysis demonstrates that both BZ and BZ-CER composites exhibit heightened hydrophilicity with thermal aging, potentially exacerbating concerns such as icing and surface erosion. Notably, the BZ-CER composite displays greater hydrophilicity compared to the BZ composite, consistent with weight change trends. These findings underscore the utility of surface wettability analysis as a valuable tool for monitoring thermo-oxidative aging in polymers and their surface behavior in response to fluid interactions, particularly within high glass transition temperature (Tg) BZ-CER systems utilized in structural composite applications.
Citation: Fluids
PubDate: 2024-04-23
DOI: 10.3390/fluids9050100
Issue No: Vol. 9, No. 5 (2024)
- Fluids, Vol. 9, Pages 101: Understanding the Influence of the Buoyancy
Sign on Buoyancy-Driven Particle Clouds
Authors: Ali O. Alnahit, Nigel Berkeley Kaye, Abdul A. Khan
First page: 101
Abstract: A numerical model was developed to investigate the behavior of round buoyancy-driven particle clouds in a quiescent ambient. The model was validated by comparing model simulations with prior experimental and numerical results and then applied the model to examine the difference between releases of positively and negatively buoyant particles. The particle cloud model used the entrainment assumption while approximating the flow field induced by the cloud as a Hill’s spherical vortex. The motion of individual particles was resolved using a particle tracking equation that considered the forces acting on them and the induced velocity field. The simulation results showed that clouds with the same initial buoyancy magnitude and particle Reynolds number behaved differently depending on whether the particles were more dense or less dense than the ambient fluid. This was found even for very low initial buoyancy releases, suggesting that the sign of the buoyancy is always important and that, therefore, the Boussinesq assumption is never fully appropriate for such flows.
Citation: Fluids
PubDate: 2024-04-23
DOI: 10.3390/fluids9050101
Issue No: Vol. 9, No. 5 (2024)
- Fluids, Vol. 9, Pages 102: A New Non-Extensive Equation of State for the
Fluid Phases of Argon, Including the Metastable States, from the Melting
Line to 2300 K and 50 GPa
Authors: Frédéric Aitken, André Denat, Ferdinand Volino
First page: 102
Abstract: A new equation of state for argon was developed with the view of extending the range of validity of the equation of state previously proposed by Tegeler et al. and obtaining a better physical description of the experimental thermodynamic data for the whole fluid region (single-phase, metastable, and saturation states). As proposed by Tegeler et al., this equation is also based on a functional form of the residual part of the reduced Helmholtz free energy. However, in this work, the fundamental equation for Helmholtz free energy was derived from the measured quantities CV(ρ, T) and P(ρ, T). The empirical description of the isochoric heat capacity CV(ρ, T) was based on an original empirical description explicitly containing the metastable states. The thermodynamic properties (internal energy, entropy, and free energy) were then obtained by combining the integration of CV(ρ, T). The arbitrary functions introduced by the integration process were deduced from a comparison between calculated and experimental pressure P(ρ, T) data. The new formulation is valid for the whole fluid region from the melting line to 2300 K and for pressures up to 50 GPa. It also predicts the existence of a maximum of the isochoric heat capacity CV along isochors, as experimentally observed in several other fluids. For many applications, an approximate form of the equation of state for the liquid phase may be sufficient. A Tait–Tammann equation is therefore proposed between the triple-point temperature and 148 K.
Citation: Fluids
PubDate: 2024-04-24
DOI: 10.3390/fluids9050102
Issue No: Vol. 9, No. 5 (2024)
- Fluids, Vol. 9, Pages 103: Analyzing the Influence of Dean Number on an
Accelerated Toroidal: Insights from Particle Imaging Velocimetry Gyroscope
(PIVG)
Authors: Ramy Elaswad, Naser El-Sheimy, Abdulmajeed Mohamad
First page: 103
Abstract: Computational Fluid Dynamics (CFD) simulations were utilized in this study to comprehensively explore the fluid dynamics within an accelerated toroidal vessel, specifically those central to Particle Imaging Velocimetry Gyroscope (PIVG) technology. To ensure the robustness of our simulations, we systematically conducted grid convergence studies and quantified uncertainties, affirming the stability, accuracy, and reliability of our computational grid and results. Comprehensive validation against experimental data further confirmed our simulations’ fidelity, emphasizing the model’s fidelity. As the PIVG is set up to address the primary flow through the toroidal pipe, we focused on the interaction between the primary and secondary flows to provide insights into the relevant dynamics of the fluid. In our investigation covering Dean numbers (De) from 10 to 70, we analyzed diverse aspects, including primary flow, secondary flow patterns, pressure distribution, and the interrelation between primary and secondary flows within toroidal structures, offering a comprehensive view across this range. Our research indicated stability and fully developed fluid dynamics within the toroidal pipe under accelerated angular velocity, particularly for low De. Furthermore, we identified an optimal Dean number of 11, which corresponded to ideal dimensions for the toroidal geometry with a curvature radius of 25 mm and a cross-sectional diameter of 5 mm. This study enhances our understanding of toroidal fluid dynamics and highlights the pivotal role of CFD in optimizing toroidal vessel design for advanced navigation technologies.
Citation: Fluids
PubDate: 2024-04-25
DOI: 10.3390/fluids9050103
Issue No: Vol. 9, No. 5 (2024)
- Fluids, Vol. 9, Pages 104: Adjoint Solver-Based Analysis of
Mouth–Tongue Morphologies on Vapor Deposition in the Upper Airway
Authors: Mohamed Talaat, Xiuhua Si, Jinxiang Xi
First page: 104
Abstract: Even though inhalation dosimetry is determined by three factors (i.e., breathing, aerosols, and the respiratory tract), the first two categories have been more widely studied than the last. Both breathing and aerosols are quantitative variables that can be easily changed, while respiratory airway morphologies are difficult to reconstruct, modify, and quantify. Although several methods are available for model reconstruction and modification, developing an anatomically accurate airway model and morphing it to various physiological conditions remains labor-intensive and technically challenging. The objective of this study is to explore the feasibility of using an adjoint–CFD model to understand airway shape effects on vapor deposition and control vapor flux into the lung. A mouth–throat model was used, with the shape of the mouth and tongue being automatically varied via adjoint morphing and the vapor transport being simulated using ANSYS Fluent coupled with a wall absorption model. Two chemicals with varying adsorption rates, Acetaldehyde and Benzene, were considered, which exhibited large differences in dosimetry sensitivity to airway shapes. For both chemicals, the maximal possible morphing was first identified and then morphology parametric studies were conducted. Results show that changing the mouth–tongue shape can alter the oral filtration by 3.2% for Acetaldehyde and 0.27% for Benzene under a given inhalation condition. The front tongue exerts a significant impact on all cases considered, while the impact of other regions varies among cases. This study demonstrates that the hybrid adjoint–CFD approach can be a practical and efficient method to investigate morphology-associated variability in the dosimetry of vapors and nanomedicines under steady inhalation.
Citation: Fluids
PubDate: 2024-04-27
DOI: 10.3390/fluids9050104
Issue No: Vol. 9, No. 5 (2024)
- Fluids, Vol. 9, Pages 105: Multi-Objective Topology Optimization of
Conjugate Heat Transfer Using Level Sets and Anisotropic Mesh Adaptation
Authors: Philippe Meliga, Wassim Abdel Nour, Delphine Laboureur, Damien Serret, Elie Hachem
First page: 105
Abstract: This study proposes a new computational framework for the multi-objective topology optimization of conjugate heat transfer systems using a continuous adjoint approach. It relies on a monolithic solver for the coupled steady-state Navier–Stokes and heat equations, which combines finite elements stabilized by the variational multi-scale method, level set representations of the fluid–solid interfaces and immersed modeling of heterogeneous materials (fluid–solid) to ensure that the proper amount of heat is exchanged to the ambient fluid by solid objects in arbitrary geometry. At each optimization iteration, anisotropic mesh adaptation is applied in near-wall regions automatically captured by the level set. This considerably cuts the computational effort associated with calling the finite element solver, in comparison to traditional topology optimization algorithms operating on isotropic grids with a comparable refinement level. Given that we operate within the constraint of a specified number of nodes in the mesh, this allows not only to improve the accuracy of interface representation and motion but also to retain the high fidelity of the numerical solutions at the grid points just adjacent to the interface. Finally, the remeshing and resolution steps both run within a highly parallel environment, which makes it possible for the proposed algorithm to tackle large-scale problems in three dimensions with several tens of millions of state degrees of freedom. The developed solver is validated first by minimizing dissipation in a flow splitter device, for which the method delivers relevant optimal designs over a wide range of volume constraints and flow rate distributions over the multiple outlet orifices but yields better accuracy compared to reference data from literature obtained using uniform meshes (in the sense that the layouts are more smooth, and the solutions are better resolved). The scheme is then applied to a two-dimensional heat transfer problem, using bi-objective cost functionals combining flow resistance and thermal recoverable power. A comprehensive parametric study reveals a complex arrangement of optimal solutions on the Pareto front, with multiple branches of symmetric and asymmetric designs, some of them previously unreported. Finally, the algorithmic developments are substantiated with several three-dimensional numerical examples tackled under fixed weights for heat transfer and flow resistance, for which we show that the optimal layouts computed at low Reynolds number, that are intrinsically relevant to a broad range of microfluidic application, can also serve as smooth solutions to high-Reynolds-number engineering problems of practical interest.
Citation: Fluids
PubDate: 2024-04-28
DOI: 10.3390/fluids9050105
Issue No: Vol. 9, No. 5 (2024)
- Fluids, Vol. 9, Pages 106: Energy Budget Characterisation of the Optimal
Disturbance in Stratified Shear Flow
Authors: Larry E. Godwin, Philip M. J. Trevelyan, Takeshi Akinaga, Sotos C. Generalis
First page: 106
Abstract: Stratified Taylor–Couette flow (STCF) undergoes transient growth. Recent studies have shown that there exists transient amplification in the linear regime of counter-rotating STCF. The kinetic budget of the optimal transient perturbation is analysed numerically to simulate the interaction of the shear production (SP), buoyancy flux (BP), and other energy components that contributes to the total optimal transient kinetic energy. These contributions affect the total energy by influencing the perturbation to extract kinetic energy (KE) from the mean flow. The decay of the amplification factor resulted from the positive amplification of both BP and SP, while the growth is attributed to the negative and positive amplification of BP and SP, respectively. The optimal SP is positively amplified, implying that there is the possibility of constant linear growth. These findings agree with the linear growth rate for increasing values of Grashof number.
Citation: Fluids
PubDate: 2024-04-29
DOI: 10.3390/fluids9050106
Issue No: Vol. 9, No. 5 (2024)
- Fluids, Vol. 9, Pages 107: Are Local Heat Transfer Quantities Useful for
Predicting the Working Behavior of Different Pulsating Heat Pipe Layouts'
A Comparative Study
Authors: Luca Pagliarini, Fabio Bozzoli
First page: 107
Abstract: Despite a continuous effort devoted by the scientific community, a large-scale employment of Pulsating Heat Pipes for thermal management applications is still nowadays undermined by the low reliability of such heat transfer systems. The main reason underlying this critical issue is linked to the strongly chaotic thermofluidic behavior of these devices, which prevents a robust prediction of their working behavior for different geometries and operating conditions, consequently hampering proper industrial design. The present work proposes to thoroughly compare data referring to previous infrared investigations on different Pulsating Heat Pipe layouts, which have focused on the estimation of heat fluxes locally exchanged at the wall–fluid interfaces. The aim is to understand the beneficial contribution of local heat transfer quantities in the prediction of the complex physics underlying such heat transfer systems. The results have highlighted that, regardless of the considered geometry and working conditions, wall-to-fluid heat fluxes are able to provide useful quantities to be employed, to some extent, to generalize Pulsating Heat Pipe operation and to improve their existing numerical models.
Citation: Fluids
PubDate: 2024-04-30
DOI: 10.3390/fluids9050107
Issue No: Vol. 9, No. 5 (2024)
- Fluids, Vol. 9, Pages 108: Study of Orifice Design on Oleo-Pneumatic Shock
Absorber
Authors: Paulo A. S. F. Silva, Ahmed A. Sheikh Al-Shabab, Panagiotis Tsoutsanis, Martin Skote
First page: 108
Abstract: Aircraft oil-strut shock absorbers rely on orifice designs to control fluid flow and optimize damping performance. However, the complex nature of cavitating flows poses significant challenges in predicting the influence of orifice geometry on energy dissipation and system reliability. This study presents a comprehensive computational fluid dynamics (CFD) analysis of the effects of circular, rectangular, semicircular, and cutback orifice profiles on the internal flow characteristics and damping behavior of oleo-pneumatic shock absorbers. High-fidelity simulations reveal that the rectangular orifice generates higher damping pressures and velocity magnitude than those generated by others designs, while the semicircular shape reduces cavitation inception and exhibits a more gradual pressure recovery. Furthermore, the study highlights the importance of considering both geometric and thermodynamic factors in the design and analysis of cavitating flow systems, as liquid properties and vapor pressure significantly impact bubble growth and collapse behavior. Increasing the orifice length had a negligible impact on damping but moderately raised orifice velocities. This research provides valuable insights for optimizing shock absorber performance across a range of operating conditions, ultimately enhancing vehicle safety and passenger comfort.
Citation: Fluids
PubDate: 2024-05-03
DOI: 10.3390/fluids9050108
Issue No: Vol. 9, No. 5 (2024)
- Fluids, Vol. 9, Pages 109: A Numerical Study on the Influence of Riparian
Vegetation Patch on the Transportation of Suspended Sediment in a U-Bend
Channel Flow
Authors: Mingyang Wang, Qian Yu, Yuan Xu, Na Li, Jing Wang, Bo Cao, Lu Wang, Eldad J. Avital
First page: 109
Abstract: Bend sections are ubiquitous in natural sandy river systems. This study employs Computational Fluid Dynamics–Discrete Phase Model (CFD-DPM) methodology to analyze particle transport dynamics in U-bend channel flows, focusing on the distinctions between partially vegetated (Case No.1) and non-vegetated (Case No.2) scenarios. The research aims to unravel the intricate relationships among bending channel-induced secondary flow, vegetation blockage, and particle aggregation, employing both quantitative and qualitative approaches. (I) The key findings reveal that vegetation near the inner walls of curved channels markedly diminishes the intensity of secondary circulation. This reduction in circulation intensity is observed not only within vegetated areas but also extends to adjacent non-vegetated zones. Additionally, the study identifies a close correlation between vertical vortices and particle distribution near the channel bed. While particle distribution generally aligns with the vortices’ margin, dynamic patch-scale eddies near vegetation patches induce deviations, creating wave-like patterns in particle distribution. (II) The application of the Probability Density Function (PDF) provides insights into the radius-wise particle distribution. In non-vegetated channels, particle distribution is primarily influenced by secondary flow and boundary layers. In contrast, the presence of vegetation leads to a complex mixing layer, altering the particle distribution pattern and maximizing PDF values in non-vegetated free flow subzones. (III) Furthermore, the research quantifies spatial–temporal sediment heterogeneity through PDF variance. The findings demonstrate that variance in non-vegetated channels increases towards the outer wall in bending regions. Vegetation-induced turbulence causes higher variance, particularly in the mixing layer subzone, underscoring the significance of eddy size in sediment redistribution. (IV) The study of vertical concentration profiles in vegetated U-bend channels offers additional insights, while secondary flow in non-vegetated channels facilitates upward sediment transport and vegetation presence, although increasing the Turbulent Kinetic Energy (TKE), restricts channel space, and impedes secondary flow, thereby reducing vertical particle suspension. Sediment concentrations are found to be higher in the lower layers of vegetated bends, contrary to the pattern in non-vegetated bends. These findings highlight the complex interplay between vegetation, secondary flow, and sediment transport, illustrating the reduced effectiveness of secondary flow in promoting vertical particle transportation in bending channels due to the vegetation obstruction.
Citation: Fluids
PubDate: 2024-05-07
DOI: 10.3390/fluids9050109
Issue No: Vol. 9, No. 5 (2024)
- Fluids, Vol. 9, Pages 110: Experimental Investigation of the Effects of
Grooves in Fe2O4/Water Nanofluid Pool Boiling
Authors: Marwa khaleel Rashid, Bashar Mahmood Ali, Mohammed Zorah, Tariq J. Al-Musawi
First page: 110
Abstract: In this study, we systematically explored how changing groove surfaces of iron oxide/water nanofluid could affect the pool boiling heat transfer. We aimed to investigate the effect of three types of grooves, namely rectangular, circular, and triangular, on the boiling heat transfer. The goal was to improve heat transfer performance by consciously changing surface structure. Comparative analyses were conducted with deionized water to provide valuable insights. Notably, the heat transfer coefficient (HTC) exhibited a significant increase in the presence of grooves. For deionized water, the HTC rose by 91.7% and 48.7% on circular and rectangular grooved surfaces, respectively. Surprisingly, the triangular-grooved surface showed a decrease of 32.9% in HTC compared to the flat surface. On the other hand, the performance of the nanofluid displayed intriguing trends. The HTC for the nanofluid diminished by 89.2% and 22.3% on rectangular and triangular grooved surfaces, while the circular-grooved surface exhibited a notable 41.2% increase in HTC. These results underscore the complex interplay between groove geometry, fluid properties, and heat transfer enhancement in nanofluid-based boiling. Hence, we thoroughly examine the underlying mechanisms and elements influencing these observed patterns in this research. The results provide important insights for further developments in this area by shedding light on how surface changes and groove geometry may greatly affect heat transfer in nanofluid-based pool boiling systems.
Citation: Fluids
PubDate: 2024-05-08
DOI: 10.3390/fluids9050110
Issue No: Vol. 9, No. 5 (2024)
- Fluids, Vol. 9, Pages 111: Wind Tunnel Experiments on Parallel
Blade–Vortex Interaction with Static and Oscillating Airfoil
Authors: Andrea Colli, Alex Zanotti, Giuseppe Gibertini
First page: 111
Abstract: This study aims to experimentally investigate the effects of parallel blade–vortex interaction (BVI) on the aerodynamic performances of an airfoil, in particular as a possible cause of blade stall, since similar effects have been observed in literature in the case of perpendicular BVI. A wind tunnel test campaign was conducted reproducing parallel BVI on a NACA 23012 blade model at a Reynolds number of 300,000. The vortex was generated by impulsively pitching a second airfoil model, placed upstream. Measurements of the aerodynamic loads acting on the blade were performed by means of unsteady Kulite pressure transducers, while particle image velocimetry (PIV) techniques were employed to study the flow field over the blade model. After a first phase of vortex characterisation, different test cases were investigated with the blade model both kept fixed at different incidences and oscillating sinusoidally in pitch, with the latter case, a novelty in available research on parallel BVI, representing the pitching motion of a helicopter main rotor blade. The results show that parallel BVI produces a thickening of the boundary layer and can induce local flow separation at incidences close to the stall condition of the airfoil. The aerodynamic loads, both lift and drag, suffer important impulsive variations, in agreement with literature on BVI, the effects of which are extended in time. In the case of the oscillating airfoil, BVI introduces hysteresis cycles in the loads, which are generally reduced. In conclusion, parallel BVI can have a detrimental impact on the aerodynamic performances of the blade and even cause flow separation, which, while not being as catastrophic as in the case of dynamic stall, has relatively long-lasting effects.
Citation: Fluids
PubDate: 2024-05-10
DOI: 10.3390/fluids9050111
Issue No: Vol. 9, No. 5 (2024)
- Fluids, Vol. 9, Pages 112: Gauging Centrifugal Instabilities in
Compressible Free-Shear Layers via Nonlinear Boundary Region Equations
Authors: Omar Es-Sahli, Adrian Sescu, Yuji Hattori
First page: 112
Abstract: Curved free shear layers emerge in many engineering problems involving complex flow geometries, such as the flow over a backward-facing step, flows with wall injection in a boundary layer, the flow inside side-dump combustors, or wakes generated by vertical axis wind turbines, among others. Previous studies involving centrifugal instabilities have mainly focused on wall-flows where Taylor instabilities between two rotating concentric cylinders or Görtler vortices in boundary layers are generated. Curved free shear layer flows, however, have not received sufficient attention, especially in the nonlinear regime. The present work investigates the development of centrifugal instabilities in a curved free shear layer flow in the nonlinear compressible regime. The compressible Navier–Stokes equations are reduced to the nonlinear boundary region equations (BREs) in a high Reynolds number asymptotic framework, wherein the streamwise wavelength of the disturbances is assumed to be much larger than the spanwise and wall-normal counterparts. We study the effect of the freestream Mach number M∞, the shear layer thickness δ, the amplitude of the incoming disturbance A, and the relative velocity difference across the shear layer ΔV on the development of these centrifugal instabilities. Our parametric study shows that, among other things, the kinetic energy of the curved shear layer flow increases with increasing ΔV and A decreases with increasing delta. It was also found that increasing the disturbance amplitude of the incoming disturbance leads to significant growth in the mushroom-like structure’s amplitude and renders the secondary instability structures more prominent, indicating increased mixing for all Mach numbers under consideration.
Citation: Fluids
PubDate: 2024-05-11
DOI: 10.3390/fluids9050112
Issue No: Vol. 9, No. 5 (2024)
- Fluids, Vol. 9, Pages 113: Reducing Aerodynamic Drag on Roof-Mounted
Lightbars for Emergency Vehicles
Authors: Michael Gerard Connolly, Malachy J. O’Rourke, Alojz Ivankovic
First page: 113
Abstract: This paper investigates the impact of contemporary lightbars on vehicle fuel efficiency with a focus on quantifying their effects on fuel consumption and exploring strategies to improve drag performance through modifications. Simulations showed an 8–11% increase in drag for square-back vehicles, with greater penalties outlined for vehicles with rear-slanting roofs. Given the moderate drag increase, the impact on the driving range, especially for electric vehicles, remains minimal, supporting the continued use of external lightbars. Positioning experiments suggest marginal drag reductions when lowering the lightbar to its lowest position due to additional drag effects that can be caused by the mounting mechanism in its condensed form. Angling the lightbar showed negligible drag increases up to an angle of 2.5 degrees, but beyond that, a 4% increase in drag was observed for every additional 2.5 degrees. Additionally, fitting drag-reducing ramps ahead of the lightbar yielded no significant drag savings. Noise analysis identified that the lightbar’s wake and rear surfaces were responsible for the largest production of noise. The optimal lightbar design was found to incorporate overflow rather than underflow and rear tapering in sync with roof curvature. Appendable clip-on devices for the lightbar, particularly rear clip-ons, demonstrated appreciable drag reductions of up to 2.5%. A final optimised lightbar design produced a minimal 2.8% drag increase when fitted onto an unmarked vehicle, representing a threefold improvement compared with the current generation of lightbars. This study advances the field of lightbar aerodynamics by precisely quantifying drag effects by using highly detailed geometry and examines the significance of optimal positioning, angle adjustment, and appendable clip-on devices in greater depth than any existing published work.
Citation: Fluids
PubDate: 2024-05-11
DOI: 10.3390/fluids9050113
Issue No: Vol. 9, No. 5 (2024)
- Fluids, Vol. 9, Pages 114: Impact of Convection Regime on Temperature
Distribution in Food Distribution Storage Box
Authors: Fabien Beaumont, Sébastien Murer, Fabien Bogard, Guillaume Polidori
First page: 114
Abstract: This study aims to optimize the thermodynamic performance of a cold storage distribution box through the integration of a ventilation system. To achieve this goal, a prototype constructed from expanded polystyrene is developed, incorporating an active ventilation system to ensure cold temperature uniformity. Thermocouples are integrated into the device to monitor the temporal temperature evolution with and without ventilation. Concurrently, a 2D thermo-aerodynamic investigation is conducted using computational fluid dynamics (CFD). The numerical modeling of the thermodynamic behavior of the cold source employs polynomial laws as input data for the computational code (UDF functions). A comparison between experimental and numerical results reveals the computational code’s accurate prediction of the temporal temperature evolution in the cold storage distribution box, particularly under forced convection conditions. The findings indicate that in the absence of ventilation, thermal exchanges primarily occur through air conduction, whereas with ventilation, exchanges are facilitated by convection. Overall, forced convection induced by the inclusion of a ventilation device enhances thermal transfers and the thermodynamic performance of the cold storage distribution box. Furthermore, air mixing limits thermal stratification, thereby facilitating temperature homogenization.
Citation: Fluids
PubDate: 2024-05-14
DOI: 10.3390/fluids9050114
Issue No: Vol. 9, No. 5 (2024)
- Fluids, Vol. 9, Pages 115: Characterization Data for the Establishment of
Scale-Up and Process Transfer Strategies between Stainless Steel and
Single-Use Bioreactors
Authors: Vincent Bernemann, Jürgen Fitschen, Marco Leupold, Karl-Heinz Scheibenbogen, Marc Maly, Marko Hoffmann, Thomas Wucherpfennig, Michael Schlüter
First page: 115
Abstract: The reliable transfer of bioprocesses from single-use bioreactors (SUBs) of different scales to conventional stainless steel stirred-tank bioreactors is of steadily growing interest. In this publication, a scale-up study for SUBs with volumes of 200 L and 2000 L and the transfer to an industrial-scale conventional stainless steel stirred-tank bioreactor with a volume of 15,000 L is presented. The scale-up and transfer are based on a comparison of mixing times and the modeling of volumetric mass transfer coefficients kLa, measured in all three reactors in aqueous PBS/Kolliphor solution. The mass transfer coefficients are compared with the widely used correlation of van’t Riet at constant stirrer tip speeds. It can be shown that a van’t Riet correlation enables a robust and reliable prediction of mass transfer coefficients on each scale for a wide range of stirrer tip speeds and aeration rates. The process transfer from single-use bioreactors to conventional stainless steel stirred-tank bioreactors is proven to be uncritical concerning mass transfer performance. This provides higher flexibility with respect to bioreactor equipment considered for specific processes.
Citation: Fluids
PubDate: 2024-05-16
DOI: 10.3390/fluids9050115
Issue No: Vol. 9, No. 5 (2024)
- Fluids, Vol. 9, Pages 116: Turbulence and Rossby Wave Dynamics with
Realizable Eddy Damped Markovian Anisotropic Closure
Authors: Jorgen S. Frederiksen, Terence J. O’Kane
First page: 116
Abstract: The theoretical basis for the Eddy Damped Markovian Anisotropic Closure (EDMAC) is formulated for two-dimensional anisotropic turbulence interacting with Rossby waves in the presence of advection by a large-scale mean flow. The EDMAC is as computationally efficient as the Eddy Damped Quasi Normal Markovian (EDQNM) closure, but, in contrast, is realizable in the presence of transient waves. The EDMAC is arrived at through systematic simplification of a generalization of the non-Markovian Direct Interaction Approximation (DIA) closure that has its origin in renormalized perturbation theory. Markovian Anisotropic Closures (MACs) are obtained from the DIA by using three variants of the Fluctuation Dissipation Theorem (FDT) with the information in the time history integrals instead carried by Markovian differential equations for two relaxation functions. One of the MACs is simplified to the EDMAC with analytical relaxation functions and high numerical efficiency, like te EDQNM. Sufficient conditions for the EDMAC to be realizable in the presence of Rossby waves are determined. Examples of the numerical integration of the EDMAC compared with the EDQNM are presented for two-dimensional isotropic and anisotropic turbulence, at moderate Reynolds numbers, possibly interacting with Rossby waves and large-scale mean flow. The generalization of the EDMAC for the statistical dynamics of other physical systems to higher dimension and higher order nonlinearity is considered.
Citation: Fluids
PubDate: 2024-05-16
DOI: 10.3390/fluids9050116
Issue No: Vol. 9, No. 5 (2024)
- Fluids, Vol. 9, Pages 117: Physical and Numerical Experimentation of Water
Droplet Collision on a Wall: A Comparison between PLIC and HRIC Schemes
for the VOF Transport Equation with High-Speed Imaging
Authors: Bruno Silva de de Lima, Martin Sommerfeld, Francisco José de de Souza
First page: 117
Abstract: Liquid films are often found in engineering applications with thicknesses ranging from micrometer scales to large scales with a wide range of applications. To optimize such systems, researchers have dedicated themselves to the development of new techniques. To further contribute to this development, the objective of this work is to present the results of the collision of water droplets on a wall by means of experimentation and numerical simulations. For physical experimentation, an injector is used to generate a chain of water droplets that collide with the opposite wall, forming a liquid film. Images of the droplets were obtained using two high-speed recording cameras. The results for different droplet sizes and impact angles are presented and the relationship between the momentum parameter and non-dimensional pool size was established. Modeling such processes is a common challenge in engineering, with different techniques having their advantages and limitations. The simulations in this work were run using the volume of fluid method, which consists of solving a transport equation for the volume fraction of each considered fluid. A correlation was found between the surface tension to momentum transport ratio, Scd, and the non-dimensional pool size for different droplet sizes and impact angles. Regions where partial depositions were most likely to occur were found via physical experiments.
Citation: Fluids
PubDate: 2024-05-16
DOI: 10.3390/fluids9050117
Issue No: Vol. 9, No. 5 (2024)
- Fluids, Vol. 9, Pages 118: A Variational Surface-Evolution Approach to
Optimal Transport over Transitioning Compact Supports with Domain
Constraints
Authors: Anthony Yezzi
First page: 118
Abstract: We examine the optimal mass transport problem in Rn between densities with transitioning compact support by considering the geometry of a continuous interpolating support boundary Γ in space-time within which the mass density evolves according to the fluid dynamical framework of Benamou and Brenier. We treat the geometry of this space-time embedding in terms of points, vectors, and sets in Rn+1=R×Rn and blend the mass density and velocity as well into a space-time solenoidal vector field W Ω→Rn+1 over a compact set Ω⊂Rn+1. We then formulate a joint optimization for W and its support using the shaped gradient of the space-time surface Γ outlining the support boundary ∂Ω. This easily accommodates spatiotemporal constraints, including obstacles or mandatory regions to visit.
Citation: Fluids
PubDate: 2024-05-16
DOI: 10.3390/fluids9050118
Issue No: Vol. 9, No. 5 (2024)
- Fluids, Vol. 9, Pages 119: Circular Fluid Heating—Transient
Entropy Generation
Authors: Fikret Alic
First page: 119
Abstract: A technical issue with fluid flow heating is the relatively small temperature increase as the fluid passes through the heating surface. The fluid does not spend enough time inside the heating source to significantly raise its temperature, despite the heating source itself experiencing a substantial increase. To address this challenge, the concept of the multiple circular heating of air was developed, forming the basis of this work. Two PTC heaters with longitudinal fins are located within a closed channel inside housing composed of a thermal insulation material. Air flows circularly from one finned surface to another. Analytical modeling and experimental testing were used in the analysis, with established restrictions and boundary conditions. An important outcome of the analysis was the methodology established for the optimization of the geometric and process parameters based on minimizing the transient thermal entropy. In conducting the analytical modeling, the temperature of the PTC heater was assumed to be constant at 150 °C and 200 °C. By removing the restrictions and adjusting the boundary conditions, the established methodology for the analysis and optimization of various thermally transient industrial processes can be applied more widely. The experimental determination of the transient thermal entropy was performed at a much higher air flow rate of 0.005 m3s−1 inside the closed channel. The minimum transient entropy also indicates the optimal time for the opening of the channel, allowing the heated air to exit. The novelty of this work lies in the controlled circular heating of the fluid and the establishment of the minimum transient thermal entropy as an optimization criterion.
Citation: Fluids
PubDate: 2024-05-18
DOI: 10.3390/fluids9050119
Issue No: Vol. 9, No. 5 (2024)
- Fluids, Vol. 9, Pages 97: Nonlinear Approach to Jouguet Detonation in
Perpendicular Magnetic Fields
Authors: Andriy A. Avramenko, Igor V. Shevchuk, Margarita M. Kovetskaya, Yulia Y. Kovetska, Andrii I. Tyrinov
First page: 97
Abstract: The focus of this paper was Jouguet detonation in an ideal gas flow in a magnetic field. A modified Hugoniot detonation equation has been obtained, taking into account the influence of the magnetic field on the detonation process and the parameters of the detonation wave. It was shown that, under the influence of a magnetic field, combustion products move away from the detonation front at supersonic speed. As the magnetic field strength increases, the speed of the detonation products also increases. A dependence has been obtained that allows us to evaluate the influence of heat release on detonation parameters.
Citation: Fluids
PubDate: 2024-04-20
DOI: 10.3390/fluids9040097
Issue No: Vol. 9, No. 4 (2024)
- Fluids, Vol. 9, Pages 98: A Note on the Moody Diagram
Authors: Paulo R. de Souza Mendes
First page: 98
Abstract: In this work, we underscore the significance of selecting an appropriate scaling to derive dimensionless quantities that accurately reflect their dimensional counterparts, thereby enhancing the comprehension of the underlying physics. For the loss of head in a pipe flow, we argue that employing inertial force (or kinetic energy) to non-dimensionalized pressure force (or mechanical energy loss) lacks physical justification. As a result, an anomalous trend emerges for the classical friction factor: it decreases as the dimensionless flow rate (Reynolds number) increases, contrary to the behavior observed in the corresponding dimensional quantities. Conversely, by non-dimensionalizing the pressure force with the viscous force, a novel friction factor arises. In laminar flow, it is constant, while in turbulent flow, it is a monotonically increasing function of the Reynolds number, mirroring the behavior observed in the dimensional problem.
Citation: Fluids
PubDate: 2024-04-21
DOI: 10.3390/fluids9040098
Issue No: Vol. 9, No. 4 (2024)
- Fluids, Vol. 9, Pages 99: A New Solution of Drag for Newtonian Fluid
Droplets in a Power-Law Fluid
Authors: Jianting Zhu
First page: 99
Abstract: Understanding flow behaviors of multiple droplets in complex non-Newtonian fluids is crucial in many science and engineering applications. In this study, a new and improved analytical solution is developed based on the free surface cell model for the flow drag of swamp of Newtonian fluid drops through a power-law fluid. The developed solution is accurate and compares well to the numerical solutions. The improvement involves a new quantification of shear stress boundary condition at the interface and a more consistent approximation in linearizing the power-law fluid flow governing equation. The Newtonian fluid solutions can be reasonably used to linearize the flow governing equation. The approximation of the boundary conditions at the interface, however, has a major impact on the model prediction. The main improvement in the new solution is observed under the condition of comparable viscosities of the Newtonian drops and the outside power-law fluid when the results are sensitive to the interface boundary condition. Under the two extreme conditions of high viscosity ratio (approaching particles) and low ratio (approaching bubbles), the present and existing solutions converge.
Citation: Fluids
PubDate: 2024-04-21
DOI: 10.3390/fluids9040099
Issue No: Vol. 9, No. 4 (2024)
