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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. 10, Pages 21: Pressure Behavior in a Linear Porous Media for
Partially Miscible Displacement of Oil by Gas
Authors: Luara K. S. Sousa, Wagner Q. Barros, Adolfo P. Pires, Alvaro M. M. Peres
First page: 21
Abstract: Miscible gas flooding improves oil displacement through mass exchange between oil and gas phases. It is one of the most efficient enhanced oil recovery methods for intermediate density oil reservoirs. In this work, analytical solutions for saturation, concentration and pressure are derived for oil displacement by a partially miscible gas injection at a constant rate. The mathematical model considers two-phase, three-component fluid flow in a one-dimensional homogeneous reservoir initially saturated by a single oil phase. Phase saturations and component concentrations are described by a 2×2 hyperbolic system of partial differential equations, which is solved by the method of characteristics. Once this Goursat–Riemann problem is solved, the pressure drop between two points in the porous media is obtained by the integration of Darcy’s law. The solution of this problem may present three different fluid regions depending on the rock–fluid parameters: a single-phase gas region near the injection point, followed by a two-phase region where mass transfer takes place and a single-phase oil region. We considered the single-phase gas and the two-phase gas/oil regions as incompressible, while the single-phase oil region may be incompressible or slightly compressible. The solutions derived in this work are applied for a specific set of rock and fluid properties. For this data set, the two-phase region displays rarefaction waves, shock waves and constant states. The pressure behavior depends on the physical model (incompressible, compressible and finite or infinite porous media). In all cases, the injection pressure is the result of the sum of two terms: one represents the effect of the mobility contrast between phases and the other represents the single-phase oil solution. The solutions obtained in this work are compared to an equivalent immiscible solution, which shows that the miscible displacement is more efficient.
Citation: Fluids
PubDate: 2025-01-21
DOI: 10.3390/fluids10020021
Issue No: Vol. 10, No. 2 (2025)
- Fluids, Vol. 10, Pages 22: The Lattice Boltzmann Method with Deformable
Boundary for Colonic Flow Due to Segmental Circular Contractions
Authors: Irina Ginzburg
First page: 22
Abstract: We extend the 3D Lattice Boltzmann method with a deformable boundary (LBM-DB) for the computations of the full-volume colonic flow of the Newtonian fluid driven by the peristaltic segmented circular contractions which obey the three-step “intestinal law”: (i) deflation, (ii) inflation, and (iii) elastic relaxation. The key point is that the LBM-DB accurately prescribes a curved deforming surface on the regular computational grid through precise and compact Dirichlet velocity schemes, without the need to recover for an adaptive boundary mesh or surface remesh, and without constraint of fluid volume conservation. The population “refill” of “fresh” fluid nodes, including sharp corners, is reformulated with the improved reconstruction algorithms by combining bulk and advanced boundary LBM steps with a local sub-iterative collision update. The efficient parallel LBM-DB simulations in silico then extend the physical experiments performed in vitro on the Dynamic Colon Model (DCM, 2020) to highly occlusive contractile waves. The motility scenarios are modeled both in a cylindrical tube and in a new geometry of “parabolic” transverse shape, which mimics the dynamics of realistic triangular lumen aperture. We examine the role of cross-sectional shape, motility pattern, occlusion scenario, peristaltic wave speed, elasticity effect, kinematic viscosity, inlet/outlet conditions and numerical compressibility on the temporal localization of pressure and velocity oscillations, and especially the ratio of retrograde vs antegrade velocity amplitudes, in relation to the major contractile events. The developed numerical approach could contribute to a better understanding of the intestinal physiology and pathology due to a possibility of its straightforward extension to the non-Newtonian chyme rheology and anatomical geometry.
Citation: Fluids
PubDate: 2025-01-21
DOI: 10.3390/fluids10020022
Issue No: Vol. 10, No. 2 (2025)
- Fluids, Vol. 10, Pages 23: Recent Developments and Future Directions in
Flow Visualization: Experiments and Techniques
Authors: Mingming Ge, Guangjian Zhang, Xinlei Zhang
First page: 23
Abstract: Flow visualization has long been a critical tool for understanding complex fluid dynamics in both natural and engineered systems [...]
Citation: Fluids
PubDate: 2025-01-22
DOI: 10.3390/fluids10020023
Issue No: Vol. 10, No. 2 (2025)
- Fluids, Vol. 10, Pages 24: Magnetohyrodynamic Turbulence in a Spherical
Shell: Galerkin Models, Boundary Conditions, and the Dynamo Problem
Authors: John V. Shebalin
First page: 24
Abstract: The ‘dynamo problem’ requires that the origin of the primarily dipole geomagneticfield be found. The source of the geomagnetic field lies within the outer core ofthe Earth, which contains a turbulent magnetofluid whose motion is described by theequations of magnetohydrodynamics (MHD). A mathematical model can be based on theapproximate but essential features of the problem, i.e., a rotating spherical shell containingan incompressible turbulent magnetofluid that is either ideal or real but maintained inan equilibrium state. Galerkin methods use orthogonal function expansions to representdynamical fields, with each orthogonal function individually satisfying imposed boundaryconditions. These Galerkin methods transform the problem from a few partial differentialequations in physical space into a huge number of coupled, non-linear ordinary differentialequations in the phase space of expansion coefficients, creating a dynamical system. Inthe ideal case, using Dirichlet boundary conditions, equilibrium statistical mechanics hasprovided a solution to the problem. As has been presented elsewhere, the solution alsohas relevance to the non-ideal case. Here, we examine and compare Galerkin methodsimposing Neumann or mixed boundary conditions, in addition to Dirichlet conditions.Any of these Galerkin methods produce a dynamical system representing MHD turbulenceand the application of equilibrium statistical mechanics in the ideal case gives solutionsof the dynamo problem that differ only slightly in their individual sets of wavenumbers.One set of boundary conditions, Neumann on the outer and Dirichlet on the inner surface,might seem appropriate for modeling the outer core as it allows for a non-zero radial componentof the internal, turbulent magnetic field to emerge and form the geomagnetic field.However, this does not provide the necessary transition of a turbulent MHD energy spectrumto match that of the surface geomagnetic field. Instead, we conclude that the modelwith Dirichlet conditions on both the outer and the inner surfaces is the most appropriatebecause it provides for a correct transition of the magnetic field, through an electricallyconducting mantle, from the Earth’s outer core to its surface, solving the dynamo problem.In addition, we consider how a Galerkin model velocity field can satisfy no-slip conditionson solid boundaries and conclude that some slight, kinetically driven compressibility mustexist, and we show how this can be accomplished.
Citation: Fluids
PubDate: 2025-01-23
DOI: 10.3390/fluids10020024
Issue No: Vol. 10, No. 2 (2025)
- Fluids, Vol. 10, Pages 25: Experimental Optimization of a Venturi-Type
Fine Bubble Generation System Based on Gas Absorption Rate
Authors: Gabriel Toma, Jesús Rafael Alcántara Avila
First page: 25
Abstract: Fine bubbles (FBs) are defined by the ISO/TC 281 as gas bubbles with a diameter of less than 100 μm, and they have interesting properties such as high surface-to-volume ratio, low buoyancy, long residence time, electric charge, and self-pressurization effect. Typically, FBs are characterized in terms of size distribution, concentration, and zeta potential through specialized microscopic and nanoscopic measuring devices. This work proposes a multi-objective optimization problem to find the optimal conditions to generate FBs from experimental macroscopic measurements in terms of dissolved oxygen (DO). Then, detailed microscopic measurements in terms of size distribution and zeta potential are conducted. Additionally, two venturi-type Fine Bubble Generators (FBGs) were 3D-printed in-house to evaluate the relationship between the internal structure and the generation of FBs. The best FBGs have an obstacle in the diverging section that promotes FB generation under the evaluated experimental conditions. Under the best operating conditions, FBs were stable over 7 days with a size distribution between 60 and 90 nm and with an average of −21 mV.
Citation: Fluids
PubDate: 2025-01-24
DOI: 10.3390/fluids10020025
Issue No: Vol. 10, No. 2 (2025)
- Fluids, Vol. 10, Pages 26: Liquid–Liquid Flow and Mass Transfer
Enhancement in Tube-in-Tube Millireactors with Structured Inserts and
Advanced Inlet Designs
Authors: Feng Zhu, Xingxing Pan, Xichun Cao, Yandan Chen, Rijie Wang, Jiande Lin, Hanyang Liu
First page: 26
Abstract: Liquid–liquid mass transfer is crucial in chemical processes like extraction and desulfurization. Traditional tube-in-tube millireactors often overlook internal flow dynamics, focusing instead on entry modifications. This study explores mass transfer enhancement through structured inserts (twisted tapes, multi-blades) and inlet designs (multi-hole injectors, T-mixers). Using high-speed imaging and water–succinic acid–butanol experiments, flow patterns and mass transfer rates were analyzed. Results show annular and dispersion flows dominate under tested conditions with structured inserts lowering the threshold for dispersion flow. Multi-hole injectors improved mass transfer by over 40% compared to T-mixers in plain tubes, while C-tape inserts achieved the highest volumetric mass transfer coefficient (2.43 s−1) due to increased interfacial area and droplet breakup from energy dissipation. This approach offers scalable solutions to enhance tube-in-tube millireactor performance for industrial applications.
Citation: Fluids
PubDate: 2025-01-24
DOI: 10.3390/fluids10020026
Issue No: Vol. 10, No. 2 (2025)
- Fluids, Vol. 10, Pages 27: Transonic Aerodynamic Performance Analysis of a
CRM Joined-Wing Configuration
Authors: Paul Hanman, Yufeng Yao, Abdessalem Bouferrouk
First page: 27
Abstract: This study examines the aerodynamic performance of a joined-wing (JW) aircraft design based on the NASA Common Research Model (CRM), aiming to assess its potential for efficient commercial transport or cargo aircraft at transonic speed (Mach 0.85). The CRM wing, optimised for transonic flight, was transformed into a JW design featuring a high-aspect-ratio main wing. An initial parametric study using the vortex lattice minimum drag panel method identified viable designs. The selected JW configuration, comprising front and rear wings joined by a vertical fin, was analysed using ANSYS Fluent to understand flow interactions and aerodynamic performance. At an angle of attack (AoA) of −1°, the JW design achieved a peak lift-to-drag ratio (L/D) of 17.45, close to the CRM’s peak L/D of 19.64 at 2°, demonstrating competitive efficiency. The JW’s L/D exceeded the CRM’s between AoA −3° and 0.8°, but the CRM performed better above 0.8°, with differences decreasing at a higher AoA. Based on induced drag alone, the JW outperformed the CRM across AoA −3° to 8°, but flow complications restricted its L/D advantage to a small, low AoA range. A strong shock on the vertical fin’s inboard side due to high incoming flow speed delayed shock formation on the main wing near the joint. Optimising the vertical fin shape slightly improved L/D, suggesting potential for further enhancements or that other design factors significantly affect JW performance. This study provides insights into JW aerodynamics at transonic speeds, revealing its potential benefits and challenges compared to the CRM design.
Citation: Fluids
PubDate: 2025-01-25
DOI: 10.3390/fluids10020027
Issue No: Vol. 10, No. 2 (2025)
- Fluids, Vol. 10, Pages 28: Features of Supersonic Flow Around a Blunt Body
in the Area of Junction with a Flat Surface
Authors: T. A. Lapushkina, E. V. Kolesnik, N. A. Monahov, P. A. Popov, K. I. Belov
First page: 28
Abstract: This work studies the influence of a growing boundary layer on the process of supersonic flow around an aerodynamic body. The task is to select and implement in an experiment the parameters of a supersonic flow and to study the flow pattern near the surface of an aerodynamic body at different viscosity values for the incoming flow. Visualization of the shock wave configuration in front of the body and studying the change in the pressure field in the flow region under these conditions is the main goal of this work. The experiment was carried out on an experimental stand created on the basis of a shock tube. The aerodynamic body under study (a semi-cylinder pointed along a circle or an ellipse) was placed in a supersonic nozzle. The model was clamped by lateral transparent walls, which were simultaneously a source of boundary layer growth and the viewing windows for visualizing the flow. For selected modes with Reynolds numbers from 8200 to 45,000, schlieren flow patterns and pressure distribution fields near the surface of the streamlined models and the plate of the growing boundary layer were obtained. The data show a complex, unsteady flow pattern realized near the model which was caused by the viscous-inviscid interaction of the boundary layer with the bow shock wave near the wall.
Citation: Fluids
PubDate: 2025-01-26
DOI: 10.3390/fluids10020028
Issue No: Vol. 10, No. 2 (2025)
- Fluids, Vol. 10, Pages 29: Updated Review on the Available Methods for
Measurement and Prediction of the Mass Transfer Coefficients in Bubble
Columns
Authors: Stoyan Nedeltchev
First page: 29
Abstract: This review summarizes the most important measurement techniques for determination of the volumetric liquid-phase mass transfer coefficient kLa. In addition, the main empirical correlations (with their applicability ranges) for kLa estimation are presented. It is clearly underlined that in tall bubble columns, a system of two differential equations (involving the gas and liquid axial dispersion coefficients) should be solved in order to obtain the accurate kLa value. The semi-empirical correlations for kLa prediction based on the correction of the penetration theory are also summarized. The need for a correction of the penetration theory is explained. The different definitions of the gas–liquid contact time, including the one based on the local isotropic turbulence theory, are presented. Finally, the various chemical methods for the determination of the gas–liquid interfacial area are summarized. Additionally, the main correlation for the prediction of the interfacial area is reported. The effects of pressure, temperature, and viscosity on the interfacial area and kLa are discussed.
Citation: Fluids
PubDate: 2025-01-27
DOI: 10.3390/fluids10020029
Issue No: Vol. 10, No. 2 (2025)
- Fluids, Vol. 10, Pages 30: Instability of a Film Falling Down a Bounded
Plate and Its Application to Structured Packing
Authors: Giulio Croce, Nicola Suzzi
First page: 30
Abstract: The instability of a film falling down a vertical plate with lateral walls, which is the base configuration describing the structured packing geometry, is numerically investigated via the lubrication theory. The solid substrate wettability is imposed through the disjoining pressure, while the assumption of a tiny, precursor film thickness allows for modelling a moving contact line. Contact angles up to 60∘, which falls in the range of structured packing applications, are investigated, thanks to the full implementation of the capillary pressure instead of the small slope approximation. Parametric computations are run for a film falling down a vertical plate bounded by lateral walls, changing the plate width and the flow characteristics. An in-house, finite volume method (FVM) code, previously developed in FORTRAN language and validated in the case of film instability and rivulet flow, is used. The number of observed rivulets, triggered by the instability induced by the lateral walls, is traced for each computation. The numerical results suggest that rivulets with a given wavelength, equal to the one provided by the linear stability analysis, are generated, but only those characterized by a wavelength greater than a minimum threshold, which depends on the substrate wettability, induce partial dewetting of the domain. This allowed for the development of a simplified, statistically based model to predict the effective interface area and the rivulet holdup (required to estimate the mass transfer rate in absorption/distillation applications). Compared to the literature models of the structured packing hydrodynamics, which usually assume a continuous wetting layer, the influence of the flow pattern (continuous film or ensemble of rivulets) on the liquid holdup and on the interfacial area is introduced. The predicted flow regime is successfully verified with evidence from the literature, involving a flow down a corrugated sheet.
Citation: Fluids
PubDate: 2025-01-27
DOI: 10.3390/fluids10020030
Issue No: Vol. 10, No. 2 (2025)
- Fluids, Vol. 10, Pages 31: Spurious Aeroacoustic Emissions in Lattice
Boltzmann Simulations on Non-Uniform Grids
Authors: Alexander Schukmann, Viktor Haas, Andreas Schneider
First page: 31
Abstract: Although there do exist a few aeroacoustic studies on harmful artificial phenomena related to the usage of non-uniform Cartesian grids in lattice Boltzmann methods (LBM), a thorough quantitative comparison between different categories of grid arrangement is still missing in the literature. In this paper, several established schemes for hierarchical grid refinement in lattice Boltzmann simulations are analyzed with respect to spurious aeroacoustic emissions using a weakly compressible model based on a D3Q19 athermal velocity set. In order to distinguish between various sources of spurious phenomena, we deploy both the classical Bhatnagar–Gross–Krook and other more recent collision models like the hybrid recursive-regularization operator, the latter of which is able to filter out detrimental non-hydrodynamic mode contributions, inherently present in the LBM dynamics. We show by means of various benchmark simulations that a cell-centered approach, either with a linear or uniform explosion procedure, as well as a vertex-centered direct-coupling method, proves to be the most suitable with regards to aeroacoustics, as they produce the least amount of spurious noise. Furthermore, it is demonstrated how simple modifications in the selection of distribution functions to be reconstructed during the communication step between fine and coarse grids affect spurious aeroacoustic artifacts in vertex-centered schemes and can thus be leveraged to positively influence stability and accuracy.
Citation: Fluids
PubDate: 2025-01-28
DOI: 10.3390/fluids10020031
Issue No: Vol. 10, No. 2 (2025)
- Fluids, Vol. 10, Pages 32: Sustaining Vaccine Potency in Cold Chain
Logistics: Numerical Analysis of Extended Cooling Duration in
Glycerol-Infused n-Tetradecane Phase-Change Materials
Authors: Tapasvi Bhatt, Naman Jain, Eddie Yin Kwee Yin Kwee Ng
First page: 32
Abstract: Vaccination cold chains depend critically on maintaining temperatures within the 2–8 ∘C range, with phase-change materials (PCMs) like n-tetradecane offering substantial potential due to their high latent heat and optimal melting characteristics. Despite extensive research on PCM melting enhancement, strategies to extend melting duration and thermal stability remain underexplored. This pioneering numerical study investigates the impact of incorporating 5% glycerol additive in n-tetradecane, aiming to decelerate the melting rate and sustain the desired temperature range over prolonged periods. This study numerically assesses the effect of a 5% glycerol additive on n-tetradecane, revealing a substantial 20.6 h extension in safe temperature maintenance, from 123.3 h in pure n-tetradecane (T) to 143.9 h with the additive (T + G). Although T reaches full melting in 121.7 h, the air temperature inside the cold box breaches 8∘C only 1.6 h after; in contrast, T + G reaches this threshold 2.2 h before full melting, resulting in an effective extension of 20.6 h. Entropy analysis shows a delayed rise in T + G, indicating enhanced thermal stability, while temperature contours confirm T + G sustains cooling until day 6, a full day beyond T. These findings highlight glycerol’s potential to modulate thermal dynamics within PCM-based cold boxes, offering a cost-effective improvement in vaccine transport sustainability.
Citation: Fluids
PubDate: 2025-01-29
DOI: 10.3390/fluids10020032
Issue No: Vol. 10, No. 2 (2025)
- Fluids, Vol. 10, Pages 33: Flow of Fluids with Pressure-Dependent
Viscosity in Between Intersecting Planes
Authors: Rhameez S. Herbst, Charis Harley, Kumbakonam R. Rajagopal
First page: 33
Abstract: The flow of an incompressible power-law fluid through a convergent channel is considered, where the viscosity is chosen to be pressure dependent. Instead of utilizing the classical similarity transformation traditionally employed when considering Jeffery-Hamel flow, allowing for purely radial solutions for the velocity field, we allow for flow in both the radial and angular directions. We develop a numerical scheme that conserves the pressure-dependent viscosity at each cell in the computational grid. We recover the classical solution to the problem, and through our numerical solutions, we observe not only that the tangential velocities are not negligible, but also that flow reversal occurs, as illustrated by solutions with varying flow regimes. Decreasing the angle of the channel causes the magnitude of the velocity to decrease, while shorter channels lead to an increase in the magnitude of the radial and tangential velocities. In the case of the latter, this could indicate that in shorter channels, the tangential velocity has a larger impact on the occurrence of flow reversal. For more varied flow regimes, the magnitude of the radial and tangential velocities increases.
Citation: Fluids
PubDate: 2025-01-30
DOI: 10.3390/fluids10020033
Issue No: Vol. 10, No. 2 (2025)
- Fluids, Vol. 10, Pages 34: AI-Driven Optimization of Breakwater Design:
Predicting Wave Reflection and Structural Dimensions
Authors: Mohammed Loukili, Soufiane El Moumni, Kamila Kotrasova
First page: 34
Abstract: Coastal defense structures play a crucial role in mitigating wave impacts; yet, existing breakwater designs often face challenges in balancing wave reflection, energy dissipation, and structural stability. This study leverages machine learning (ML) to predict the optimal 2D dimensions of rectangular breakwaters in two configurations: submerged at the bottom of a wave tank and positioned at the free surface. Further, the objective is to achieve controlled wave reflection allowing a specific wave run-up and optimized energy dissipation, while ensuring maritime stability. Thus, we used an analytical equation modeling the reflection coefficient versus relative water depth (KH), for different immersion ratios of obstacle (h/H), and relative length (l/H). Two datasets of 32,000 data points were generated for underwater and free-surface breakwaters, with an additional 10,000 data points for validation, totaling 42,000 data points per case. Five ML algorithms—Random Forest, Support Vector Regression, Artificial Neural Network, Decision Tree, and Gaussian Process—were applied and evaluated. Results demonstrated that Random Forest and Decision Tree balanced accuracy with computational efficiency, while the Gaussian Process closely matched analytical results but demanded higher computational resources. These findings support ML as a powerful tool to optimize breakwater design, complementing traditional methods and contributing to more sustainable and resilient coastal defense systems.
Citation: Fluids
PubDate: 2025-01-30
DOI: 10.3390/fluids10020034
Issue No: Vol. 10, No. 2 (2025)
- Fluids, Vol. 10, Pages 35: Analysis of Flow Past a Double-Slanted Ahmed
Body
Authors: Matthew Aultman, Lian Duan
First page: 35
Abstract: For this study, Improved Delayed Detached-Eddy Simulations (IDDES) were used to analyze the wake of a modified Ahmed body with varying upper and lower slants. The modified geometry produced a constant projected vertical base area, ensuring that the base and slant drag were a function of the pressure caused by the wake structures. Except at extreme slant angles, the general structures of the wake were a base torus with two pairs of streamwise-oriented vortices on each slant. These structures strongly correlated with the drag contribution of the rear surfaces: the torus with the vertical base and the streamwise-oriented vortices with the slants. As such, the base drag was minimized when the torus was most centrally aligned with the base, producing the largest stagnation region. Two slant-drag minima developed corresponding to two regimes of vortical flow on opposing slants. On one slant, the vortices were attached, and the drag correlated with the size and strength of the vortices. On the other slant, the vortices separated, and the drag correlated with the slant normal due to a more uniform pressure. This demonstrates a rich and complex set of interactions that must be managed in the development of base drag caused by wake flows.
Citation: Fluids
PubDate: 2025-01-31
DOI: 10.3390/fluids10020035
Issue No: Vol. 10, No. 2 (2025)
- Fluids, Vol. 10, Pages 36: Hydrological Response of Land Use and Climate
Change Impact on Sediment Rate in Upper Citarum Watershed
Authors: Evi Anggraheni, Abdul Halim Hamdany, Farouk Maricar, Neil Andika, Dian Sisinggih, Fransiskus Sean Tanlie, Fransiskus Adinda Rio Respati
First page: 36
Abstract: The Citarum Watershed is indeed a critical water resource in Indonesia, playing a significant role in providing water to Jakarta and other areas in West Java. However, it faces severe environmental stress due to land use changes and climate changes. The Upper Citarum Watershed, considered to be a conservation area, has experienced rapid development due to human activities and economic growth. Climate change not only affects the rainfall value but also the rainfall patterns and sediment flow. The sedimentation process significantly impacts the soil characteristics around the river body. Several factors such as topography, flow velocity, and soil texture influence the sediment characteristics. Given the critical condition of climate and land use change, this study aims to analyse the impacts of the hydrological response of land use and climate change on the sediment rate in the Upper Citarum Watershed. The land use change analysis was conducted by comparing the land use data in 2000, 2010, and 2023 in the Upper Citarum Watershed. The deposition process of solid particles such as sand, silt, and gravel that are transported in the Upper Citarum River were examined in a soil investigation. The sediment rate and deposition by river flow were analysed using HEC-RAS quasi-unsteady flow. The impact of climate change in this study was assessed by simulating the discharge in three conditions, with the first simulation using the discharge from 2000 to 2010, the second simulation using the discharge from 2011 to 2023, and the last simulation using the discharge from 2000 to 2023. Due to the land use change, the developed area increased from 4% to 24% between 2000 until 2023. The magnitude of low flow during the simulation step for three discharge gauges (Majalaya, Dayeuhkolot, and Nanjung) decreased up to 48%, but, on other hand, the sediment rate increased by 20% in Dayeuhkolot.
Citation: Fluids
PubDate: 2025-01-31
DOI: 10.3390/fluids10020036
Issue No: Vol. 10, No. 2 (2025)
- Fluids, Vol. 10, Pages 37: Towards Efficient Bio-Methanation: A
Comparative Analysis of Disperser Designs and Process Optimization in
Bubble Columns
Authors: Florian Klapal, Mark Werner Hlawitschka
First page: 37
Abstract: This study aims to contribute to the optimization of bio-methanation in bubble columns, making it a more viable alternative to stirred tank reactors. The primary challenge to be addressed is the enhancement of mass transfer, which strongly depends on parameters such as bubble size and gas hold-up. Various disperser designs were examined in a 0.14 mm diameter column, comparing their performance in terms of bubble diameter distribution and gas hold-up. The results indicate that an optimized plate disperser featuring a porous structure outperformed other designs by maintaining high gas retention without significant coalescence. Additionally, newly developed plug-in dispersers allowed for counter-current flow operation, enhancing process flexibility. Commercially available porous pin dispersers produced smaller bubbles compared to the other designs, yielding high gas hold-ups at lower gas velocities. Correlations between disperser type and column design parameters were established, laying the foundation for apparatus optimization. The findings contribute to the development of digital twin models, facilitating the refinement of bio-methanation processes within bubble columns for increased efficiency.
Citation: Fluids
PubDate: 2025-01-31
DOI: 10.3390/fluids10020037
Issue No: Vol. 10, No. 2 (2025)
- Fluids, Vol. 10, Pages 38: An Application of Upwind Difference Scheme with
Preconditioned Numerical Fluxes to Gas-Liquid Two-Phase Flows
Authors: Tianmu Zhao, Byeongrog Shin
First page: 38
Abstract: A time-consistent upwind difference scheme with a preconditioned numerical flux for unsteady gas-liquid multiphase flows is presented and applied to the analysis of cavitating flows. The fundamental equations were formulated in general curvilinear coordinates to apply to diverse flow fields. The preconditioning technique was applied specifically to the numerical dissipation terms in the upwinding process without changing the time derivative terms to maintain time consistency. This approach enhances numerical stability in unsteady multiphase flow computations, consistently delivering time-accurate solutions compared to conventional preconditioning methods. A homogeneous gas-liquid two-phase flow model, third-order Runge-Kutta method, and the flux difference splitting upwind scheme coupled with a third-order MUSCL TVD scheme were employed. Numerical tests of two-dimensional gas-liquid single- and two-phase flows over backward-facing step with different step height and flow conditions successfully demonstrated the capability of the present scheme. The calculations remained stable even for flows with a very low Mach number of 0.001, typically considered incompressible flows, and the results were in good agreement with the experimental data. In addition, we analyzed unsteady cavitating flows at high Reynolds numbers and confirmed the effectiveness and applicability of the present scheme for calculating unsteady gas-liquid two-phase flows.
Citation: Fluids
PubDate: 2025-02-01
DOI: 10.3390/fluids10020038
Issue No: Vol. 10, No. 2 (2025)
- Fluids, Vol. 10, Pages 8: Fluids and Surfaces
Authors: Manfredo Guilizzoni
First page: 8
Abstract: Fluids is pleased to present a Special Issue named “Fluids and Surfaces”, a curated collection of ten research articles focused on capillary phenomena and the interaction between fluids and surfaces [...]
Citation: Fluids
PubDate: 2025-01-06
DOI: 10.3390/fluids10010008
Issue No: Vol. 10, No. 1 (2025)
- Fluids, Vol. 10, Pages 9: Literature Review on Single and Twin-Screw
Extruders Design for Polymerization Using CFD Simulation
Authors: Elham Delvar, Inês Oliveira, Margarida S. C. A. Brito, Cláudia G. Silva, Arantzazu Santamaria-Echart, Maria-Filomena Barreiro, Ricardo J. Santos
First page: 9
Abstract: This work presents a comprehensive review of the evolution in modeling reactive extrusion (REx), tracing developments from early analytical models to advanced computational fluid dynamics (CFD) simulations. Additionally, it highlights the key challenges and future directions in this field. Analytical models to describe the velocity profiles were proposed in the 1950s, involving certain geometrical simplifications. However, numerical models of melt polymeric flow in extruders have proven to be crucial for optimizing screw design and predicting process characteristics. The state-of-the-art CFD models for single and twin-screw extruders design address the impact of geometry (type of mixing elements and geometrical simplifications of CFD geometries), pressure and temperature gradients, and quantification of mixing. Despite the extensive work conducted, modeling reactive extrusion using CFD remains challenging due to the intricate interplay of mixing, heat transfer, chemical reactions, and non-Newtonian fluid behavior under high shear and temperature gradients. These challenges are further intensified by the presence of multiphase flows and the complexity of extruder geometries. Future advancements should enhance simulation accuracy, incorporate multiphase flow models, and utilize real-time sensor data for adaptive modeling approaches.
Citation: Fluids
PubDate: 2025-01-07
DOI: 10.3390/fluids10010009
Issue No: Vol. 10, No. 1 (2025)
- Fluids, Vol. 10, Pages 10: Predictive Analysis of Structural Damage in
Submerged Structures: A Case Study Approach Using Machine Learning
Authors: Alexandre Brás dos Santos, Hugo Mesquita Vasconcelos, Tiago M. R. M. Domingues, Pedro J. S. C. P. Sousa, Susana Dias, Rogério F. F. Lopes, Marco L. P. Parente, Mário Tomé, Adélio M. S. Cavadas, Pedro M. G. P. Moreira
First page: 10
Abstract: This study focuses on the development of a machine learning (ML) model to elaborate on predictions of structural damage in submerged structures due to ocean states and subsequently compares it to a real-life case of a 6-month experiment with a benthic lander bearing a multitude of sensors. The ML model uses wave parameters such as height, period and direction as input layers, which describe the ocean conditions, and strains in selected points of the lander structure as output layers. To streamline the dataset generation, a simplified approach was adopted, integrating analytical formulations based on Morison equations and numerical simulations through the Finite Element Method (FEM) of the designed lander. Subsequent validation involved Fluid–Structure Interaction (FSI) simulations, using a 2D Computational Fluid Dynamics (CFD)-based numerical wave tank of the entire ocean depth to access velocity profiles, and a restricted 3D CFD model incorporating the lander structure. A case study was conducted to empirically validate the simulated ML model, with the design and deployment of a benthic lander at 30 m depth. The lander was monitored using electrical and optical strain gauges. The strains measured during the testing period will provide empirical validation and may be used for extensive training of a more reliable model.
Citation: Fluids
PubDate: 2025-01-07
DOI: 10.3390/fluids10010010
Issue No: Vol. 10, No. 1 (2025)
- Fluids, Vol. 10, Pages 11: RETRACTED: Fatunmbi et al. Irreversibility
Analysis for Eyring–Powell Nanoliquid Flow Past Magnetized Riga
Device with Nonlinear Thermal Radiation. Fluids 2021, 6, 416
Authors: Ephesus Olusoji Fatunmbi, Adeshina Taofeeq Adeosun, Sulyman Olakunle Salawu
First page: 11
Abstract: The Fluids Editorial Office retracts the article “Irreversibility Analysis for Eyring–Powell Nanoliquid Flow Past Magnetized Riga Device with Nonlinear Thermal Radiation” [...]
Citation: Fluids
PubDate: 2025-01-08
DOI: 10.3390/fluids10010011
Issue No: Vol. 10, No. 1 (2025)
- Fluids, Vol. 10, Pages 12: On the Effect of Gas Content in Centrifugal
Pump Operations with Non-Newtonian Slurries
Authors: Nicola Zanini, Alessio Suman, Mattia Piovan, Michele Pinelli
First page: 12
Abstract: Non-Newtonian fluids are widespread in industry, e.g., biomedical, food, and oil and gas, and their rheology plays a fundamental role in choosing the processing parameters. Centrifugal pumps are widely employed to ensure the displacement of a huge amount of fluids due to their robustness and reliability. Since the pump performance is usually provided by manufacturers only for water, the selection of a proper pump to handle non-Newtonian fluids may prove very tricky. On-field experiences in pump operations with non-Newtonian slurries report severe head and efficiency drops, especially in part-load operations, whose causes are still not fully understood. Several models are found in the literature to predict the performance of centrifugal pumps with this type of fluids, but a lack of reliability and generality emerges. In this work, an extensive experimental campaign is carried out with an on-purpose test bench to investigate the effect of non-Newtonian shear-thinning fluids on the performance of a small commercial centrifugal pump. A dedicated experimental campaign is conducted to study the causes of performance drops. The results allow to establish a relationship between head and efficiency drops with solid content in the mixture. Sudden performance drops and unstable operating points are detected in part-load operations and the most severe drops are detected with the higher kaolin content in the mixture. Performance drop investigation allows to ascribe performance drop to gas-locking phenomena. Finally, a critical analysis is proposed to relate the resulting performance with both fluids’ rheology and the gas fraction trapped in the fluid. The results here presented can be useful for future numerical validation and predicting performance models.
Citation: Fluids
PubDate: 2025-01-08
DOI: 10.3390/fluids10010012
Issue No: Vol. 10, No. 1 (2025)
- Fluids, Vol. 10, Pages 13: Impact of Rock Cuttings on Downhole Fluid
Movement in Polycrystalline Diamond Compact (PDC) Bits, Computational
Fluid Dynamics, Simulation, and Optimization of Hydraulic Structures
Authors: Lihong Wei, Jaime Honra
First page: 13
Abstract: The flow occurring at the bottom of a polycrystalline diamond compact (PDC) drill bit involves a complex process made up of drilling fluid and the drilled rock cuttings. A thorough understanding of the bottom-hole flow conditions is essential for accurately evaluating and optimizing the hydraulic structure design of the PDC drill bit. Based on a comprehensive understanding of the hydraulic structure and fluid flow characteristics of PDC drill bits, this study integrates computational fluid dynamics (CFD) with rock-breaking simulation methods to refine and enhance the numerical simulation approach for the liquid–solid two-phase flow field of PDC drill bits. This study further conducts a comparative analysis of simulation results between single-phase and liquid–solid two-phase flows, highlighting the influence of rock cuttings on flow dynamics. The results reveal substantial differences in flow behavior between single-phase and two-phase conditions, with rock cuttings altering the velocity distribution, flow patterns, and hydraulic performance near the bottom-hole region of the drill bit. The two-phase flow simulation results demonstrate higher accuracy and provide a more detailed depiction of the bottom-hole flow, facilitating the identification of previously unrecognized issues in the hydraulic structure design. These findings advance the methodology for multiphase flow simulation in PDC drill bit studies, providing significant academic and engineering value by offering actionable insights for optimizing hydraulic structures and extending bit life.
Citation: Fluids
PubDate: 2025-01-14
DOI: 10.3390/fluids10010013
Issue No: Vol. 10, No. 1 (2025)
- Fluids, Vol. 10, Pages 14: Impact of Solid Particle Concentration and
Authors: Sadra Mahmoudi, Mark W. Hlawitschka
First page: 14
Abstract: In this study, in a three-phase reactor with a rectangular cross-section, the effects of liquid circulation rates and solid particle concentration on gas holdup and bubble size distribution (BSD) were investigated. Air, water, and glass beads were used as the gas, liquid, and solid phases, respectively. Different liquid circulation velocities and different solid loads were applied. The results demonstrate that increasing solid content from 0% to 6% can decrease gas holdup by 50% (due to increased slurry phase viscosity and promotion of bubble coalescence). Also, increasing the liquid circulation rate showed a weak effect on gas holdup, although a slight incremental effect was observed due to the promotion of bubble breakup and the extension of bubble residence time. The gas holdup in counter-current slurry bubble columns (CCSBCs) was predicted using a novel correlation that took into account the combined effects of solid concentration and liquid circulation rate. These findings are crucial for the design and optimization of the three-phase reactors used in industries such as mining and wastewater treatment.
Citation: Fluids
PubDate: 2025-01-16
DOI: 10.3390/fluids10010014
Issue No: Vol. 10, No. 1 (2025)
- Fluids, Vol. 10, Pages 15: Industrial CFD and Fluid Modelling in
Engineering
Authors: Francesco De Vanna
First page: 15
Abstract: Fluids is proud to present the Special Issue “Industrial CFD and Fluid Modelling in Engineering”, a carefully curated collection of pioneering research that underscores the transformative role of Computational Fluid Dynamics (CFD) in addressing the challenges of industrial fluid mechanics [...]
Citation: Fluids
PubDate: 2025-01-17
DOI: 10.3390/fluids10010015
Issue No: Vol. 10, No. 1 (2025)
- Fluids, Vol. 10, Pages 16: Transformations in Flow Characteristics and
Fluid Force Reduction with Respect to the Vegetation Type and Its
Installation Position Downstream of an Embankment
Authors: A H M Rashedunnabi, Norio Tanaka, Md Abedur Rahman
First page: 16
Abstract: Compound mitigation systems, integrations of natural and engineering structures against the high inundating current from tsunamis or storm surges, have garnered significant interest among researchers, especially following the Tohoku earthquake and tsunami in 2011. Understanding the complex flow phenomena is essential for the resilience of the mitigation structures and effective energy reduction. This study conducted a flume experiment to clarify flow characteristics and fluid force dissipation in a compound defense system. Vegetation models (V) with different porosities (Φ) were placed at three different positions downstream of an embankment model (E). A single-layer emergent vegetation model was considered, and a short-layer vegetation with several values of Φ was incorporated to increase its density (decreased Φ). Depending on Φ and the spacing (S) between the E and V, hydraulic jumps occurred in the physical system. The findings demonstrated that a rise in S allowed a hydraulic jump to develop inside the system and contributed to reducing the fluid force in front and downstream of V. Due to the reduced porosity of the double-layer vegetation, the hydraulic jump moved upstream and terminated within the system, resulting in a uniform water surface upstream of V and downstream of the system. As a result, the fluid force in front of and behind V reduced remarkably.
Citation: Fluids
PubDate: 2025-01-17
DOI: 10.3390/fluids10010016
Issue No: Vol. 10, No. 1 (2025)
- Fluids, Vol. 10, Pages 17: Three-Dimensional Aeroelastic Investigation of
a Novel Convex Bladed H-Darrieus Wind Turbine Based on a Two-Way Coupled
Computational Fluid Dynamics and Finite Element Analysis Approach
Authors: Tarek Elbeji, Wael Ben Amira, Khaled Souaissa, Moncef Ghiss, Hatem Bentaher, Nabil Ben Fredj
First page: 17
Abstract: H-Darrieus vertical-axis wind turbines (VAWTs) capture wind regardless of its direction and operate effectively even in challenging and turbulent wind conditions. As a result, the blades operate under erratic and intricate aerodynamic loads, which cause them to bend. The performance of the H-Darrieus rotor will therefore be impacted by the blade’s deflection. This study aims at investigating the dynamic aerostructure influence on a novel convex-bladed H-Darrieus geometry. The results are compared to a straight-bladed baseline rotor. To do so, a two-way fluid–structure interaction (FSI)-coupled approach is performed to accurately address this issue. This approach allows for the simultaneous resolution of the fluid flow around the rotor and the mechanical structure responses inside the blades. The turbulent flows are resolved using the k-ω-SST model together with the URANS equations through computational fluid dynamics (CFD), while the structural deflections of the blades are assessed using finite element analysis (FEA). The results show that the performance of both H-Darrieus turbines decreases with increasing deformation. In addition, the study found that the carbon fiber composite (M1) material has the least deformation in the convex and straight blades, with values of 9.1 mm and 20.331 mm, respectively. The glass-fiber-reinforced epoxy composite (M3) material shows the most significant deflection across both types, with displacements of 32.50 mm and 73.78 mm for the straight blade and 19.02 mm and 43.03 mm for the convex blade. This study also reveals that the straight blade has a peak displacement of 73.785 mm when using the M3 material at TSR = 3, while the convex blade has a minimum displacement of 20.331 mm when using the M1 material, highlighting the varying performance characteristics of the materials. The maximum stress observed occurs in the straight blade, registering at 324.1 MPa with TSR = 3, which aligns closely with the peak displacement values, particularly for the aluminum alloy material (M2). In contrast, the convex blade made from the first material (M1) exhibits the lowest stress levels among the tested configurations.
Citation: Fluids
PubDate: 2025-01-18
DOI: 10.3390/fluids10010017
Issue No: Vol. 10, No. 1 (2025)
- Fluids, Vol. 10, Pages 18: Parametric Instabilities in Time-Varying
Compressible Linear Flows
Authors: Ioannis Kiorpelidis, Nikolaos A. Bakas
First page: 18
Abstract: The stability of time-dependent compressible linear flows, which are characterized by periodic variations in either their shape or their shear, is investigated. Two novel parametric instabilities are found: an instability that occurs for periodically wobbling elliptic vortices at a number of discrete oscillation frequencies that are proportional to the Mach number and an instability that occurs for all linear flows at various frequencies of the shear oscillation that depend on the Mach number. In addition, the physical mechanism underlying the instabilities is explained in terms of the linear interaction of three waves with time-varying wavevectors that describe the evolution of perturbations: a vorticity wave representing the evolution of incompressible perturbations and two counter-propagating acoustic waves. Elliptical instability occurs because the scale of the acoustic waves decreases exponentially and their wave action is conserved, leading to an exponential increase in the acoustic waves’ energies. The instability in shear-varying flows is driven by the interaction between vorticity and the acoustic waves, which couple through the shear and for specific frequencies resonate parametrically, leading to exponential or linear growth.
Citation: Fluids
PubDate: 2025-01-18
DOI: 10.3390/fluids10010018
Issue No: Vol. 10, No. 1 (2025)
- Fluids, Vol. 10, Pages 19: Vaporization Dynamics of a Volatile Liquid Jet
on a Heated Bubbling Fluidized Bed
Authors: Subhasish Mitra, Geoffrey M. Evans
First page: 19
Abstract: In this paper, droplet vaporization dynamics in a heated bubbling fluidized bed was studied. A volatile hydrocarbon liquid jet comprising acetone was injected into a hot bubbling fluidized bed of Geldart A-type glass ballotini particles heated at 150 °C, well above the saturation temperature of acetone (56 °C). Intense interactions were observed among the evaporating droplets and hot particles during contact with the re-suspension of particles due to a release of vapour. A non-intrusive schlieren imaging method was used to track the hot air and vapour mixture plume in the freeboard region of the bed and the acetone vapour fraction therein was mapped. The jet vaporization dynamics in the bubbling fluidized bed was modelled in a Eulerian–Lagrangian CFD (computational fluid dynamics) modelling framework involving heat and mass transfer sub models. The CFD model indicated a dispersion of the vapour plume from the evaporating droplets which was qualitatively compared with the schlieren images. Further, the CFD simulation predicted a significant reduction (~60 °C) in the local bed temperature at the point of the jet injection, which was indirectly confirmed in an experiment by the presence of particle agglomerates.
Citation: Fluids
PubDate: 2025-01-18
DOI: 10.3390/fluids10010019
Issue No: Vol. 10, No. 1 (2025)
- Fluids, Vol. 10, Pages 20: Machine Learning Model for Gas–Liquid
Interface Reconstruction in CFD Numerical Simulations
Authors: Tamon Nakano, Michele Alessandro Bucci, Jean-Marc Gratien, Thibault Faney
First page: 20
Abstract: The volume of fluid (VoF) method is widely used in multiphase flow simulations to track and locate the interface between two immiscible fluids. The relative volume fraction in each cell is used to recover the interface properties (i.e., normal, location, and curvature). Accurate computation of the local interface curvature is essential for evaluation of the surface tension force at the interface. However, this interface reconstruction step is a major bottleneck of the VoF method due to its high computational cost and low accuracy on unstructured grids. Recent attempts to apply data-driven approaches to this problem have outperformed conventional methods in many test cases. However, these machine learning-based methods are restricted to computations on structured grids. In this work, we propose a machine learning-enhanced VoF method based on graph neural networks (GNNs) to accelerate interface reconstruction on general unstructured meshes. We first develop a methodology for generating a synthetic dataset based on paraboloid surfaces discretized on unstructured meshes to obtain a dataset akin to the configurations encountered in industrial settings. We then train an optimized GNN architecture on this dataset. Our approach is validated using analytical solutions and comparisons with conventional methods in the OpenFOAM framework on a canonical test. We present promising results for the efficiency of GNN-based approaches for interface reconstruction in multiphase flow simulations in the industrial context.
Citation: Fluids
PubDate: 2025-01-20
DOI: 10.3390/fluids10010020
Issue No: Vol. 10, No. 1 (2025)
- Fluids, Vol. 9, Pages 270: Non-Uniform Turbulence Modeling in Isolated
Authors: Benjamin L. Holtmann, Nicole L. Key
First page: 270
Abstract: Recent advancements in computational fluid dynamics (CFD) enable new and more complex analysis methods to be developed for early design stages. One such method is the isolated unsteady diffuser model, which seeks to reduce the computational cost of unsteady CFD when modeling diffusion systems in centrifugal compressors with vaned diffusers by isolating the diffuser from the computational domain and prescribing an unsteady and periodic inlet boundary condition. An initial iteration of this computational methodology was developed and validated for the Centrifugal Stage for Aerodynamic Research (CSTAR) at the High-Speed Compressor Laboratory at Purdue University. However, that work showed discrepancies in flow structure predictions between full-stage and isolated unsteady CFD models, and it also presented a narrow scope of only a single loading condition. Thus, this work addresses the need for improvement in the modeling fidelity. The original methodology was expanded by including a more accurate, non-uniform definition of turbulence at the diffuser inlet and modeling several loading conditions ranging from choke to surge. Results from isolated unsteady diffuser models with non-uniform turbulence modeling were compared with uniform turbulence isolated unsteady diffuser models and full-stage unsteady models at four loading conditions along a speedline. Flow structure predictions by the three methodologies were compared using 1D parameters and outlet total pressure and midspan velocity contours. The comparisons indicate a significant improvement in 1D parameter and flow structure predictions by the isolated unsteady diffuser models at all four loading conditions when including more accurate non-uniform turbulence, without a corresponding increase in computational cost. Additionally, both isolated diffuser methodologies accurately track trends in 3D flow structures along the speedline.
Citation: Fluids
PubDate: 2024-11-21
DOI: 10.3390/fluids9120270
Issue No: Vol. 9, No. 12 (2024)
- Fluids, Vol. 9, Pages 271: A Mixed-Elastohydrodynamic Lubrication Model of
a Capped-T-Ring Seal with a Sectioned Multi-Material Film Thickness in
Landing Gear Shock Absorber Applications
Authors: Aaron Feria Alanis, Ahmed A. Sheikh Al-Shabab, Antonis F. Antoniadis, Panagiotis Tsoutsanis, Martin Skote
First page: 271
Abstract: Numerical investigations of capped T-ring (CTR) seals performance in reciprocating motion for landing gear shock absorber applications are presented. A lubrication model using the Elastohydrodynamic lubrication theory and deformation mechanics is developed in a multi-material contact zone, and a procedure for coupling fluid and deformation mechanics is introduced. By conducting Finite Element Method (FEM) simulations, the static contact pressure is obtained, which subsequently is used within the model developed herein consisting of a modified Reynolds equation and an asperity contact model, to calculate the fluid film pressure, and the deformation of the fluid channel is determined using an elastic deformation model applied to a multi-component multi-mechanical property channel. These computational results are used for estimations of the seal leakage and friction under various conditions. In addition, the influence of asperity orientation is compared with other parameters, such as sealing pressure and piston velocity. A correlation between asperity orientation and leakage was found, and a general trend of reduced leakage with longitudinally oriented asperities was established.
Citation: Fluids
PubDate: 2024-11-21
DOI: 10.3390/fluids9120271
Issue No: Vol. 9, No. 12 (2024)
- Fluids, Vol. 9, Pages 272: Non-Newtonian Convective Heat Transfer in
Annuli: Numerical Investigation on the Effects of Staggered Helical Fins
Authors: Luca Pagliarini, Fabio Bozzoli, Rasoul Fallahzadeh, Sara Rainieri
First page: 272
Abstract: Despite non-Newtonian fluids being involved in many industrial processes, e.g., in food and chemical industries, their thermal treatment still represents a significant challenge due to their generally high apparent viscosity and consequent low heat transfer capability. Heat transfer in heat exchangers can be enhanced by passive systems, such as inserts or fins, to promote boundary layer disruption and fluid recirculation. However, most of the existing configurations cannot significantly improve the heat transfer over pressure drops in deep laminar flows. The present paper presents a numerical investigation on non-Newtonian flows passing through the annulus side of a double-pipe heat exchanger with staggered helical fins. The adopted geometry was conceptualized by merging the beneficial effects of swirling flow devices and boundary layer disruption. The numerical results were first validated against analytical solutions for non-Newtonian flows in annuli under a laminar flow regime. The finned geometry was therefore numerically tested and compared with the bare annulus to quantify the resulting heat transfer augmentation. When compared with the bare annuli, the proposed novel geometry greatly enhanced the heat transfer while mitigating friction losses.
Citation: Fluids
PubDate: 2024-11-21
DOI: 10.3390/fluids9120272
Issue No: Vol. 9, No. 12 (2024)
- Fluids, Vol. 9, Pages 273: Numerical Analysis of Knudsen Number of Helium
Flow Through Gas-Focused Liquid Sheet Micro-Nozzle
Authors: Krištof Kovačič, Saša Bajt, Božidar Šarler
First page: 273
Abstract: This work aims to verify whether the continuum mechanics assumption holds for the numerical simulation of a typical sample delivery system in serial femtosecond crystallography (SFX). Knudsen numbers were calculated based on the numerical simulation results of helium flow through the gas-focused liquid sheet nozzle into the vacuum chamber, representing the upper limit of Knudsen number for such systems. The analysed flow is considered steady, compressible, and laminar. The numerical results are mesh-independent, with a Grid Convergence Index significantly lower than 1% for global and local analysis. This study is based on an improved definition of the numerical Knudsen number: a combination of the cell Knudsen number and the physical Knudsen number. In the analysis, no-slip boundary and low-pressure boundary slip conditions are compared. No significant differences are observed. This study justifies using computational fluid dynamics (CFD) analysis for SFX sample delivery systems based on the assumption of continuum mechanics.
Citation: Fluids
PubDate: 2024-11-22
DOI: 10.3390/fluids9120273
Issue No: Vol. 9, No. 12 (2024)
- Fluids, Vol. 9, Pages 274: Understanding the Application of Emulsion
Systems for Bacterial Encapsulation and Temperature-Modulated Release
Authors: Nur Suaidah Mohd Isa, Hani El Kadri, Daniele Vigolo, Nur Farra Adlina Mohamed Zakhari, Konstantinos Gkatzionis
First page: 274
Abstract: The encapsulation of bacteria in emulsion droplets offers various advantages over other conventional methods of encapsulation, such as improvements in bacterial viability, and may serve as microenvironments for bacterial growth. Nevertheless, changes in temperature may affect bacterial viability and droplet stability. In this study, the encapsulation of bacteria in single water-in-oil (W/O) and double water-in-oil-in-water (W1/O/W2) emulsions under cold storage and temperature-modulated release were investigated. The microencapsulation of bacteria in emulsion droplets was achieved by using a flow-focusing microfluidic device. Droplet stability was determined by measuring changes in droplet size and creaming behaviour at different temperatures. The thermal properties of the samples were determined by using differential scanning calorimetry, while the release of bacteria with changes in temperature was determined by measuring the colony form unit (CFU) of the released bacteria and conducting fluorescence microscopy. Higher bacterial viability was observed for encapsulated samples compared to free cells, indicating the ability of the emulsion system to improve bacterial viability during cold-temperature storage. The crystallisation temperature was lowered in the presence of bacteria, but the melting temperature was similar with or without bacteria. Storage in freezing temperatures of −20 °C and −80 °C led to extensive droplet destabilisation, with the immediate release of encapsulated bacteria upon thawing, where the temperature-modulated release of encapsulated bacteria was achieved. This study provides an overview of the potential application of emulsion droplets for bacterial encapsulation under cold-temperature storage and the controlled release of encapsulated bacteria mediated by changes in temperature, which is beneficial for various applications in industries such as food and pharmaceuticals.
Citation: Fluids
PubDate: 2024-11-22
DOI: 10.3390/fluids9120274
Issue No: Vol. 9, No. 12 (2024)
- Fluids, Vol. 9, Pages 275: A Simple Mathematical Model to Predict the
Pressure Drop for Transport of Deformable Particles in Homogeneous Porous
Media
Authors: Víctor Matías-Pérez, Simón López-Ramírez, Elizbeth Franco-Urresti, Carlos G. Aguilar-Madera
First page: 275
Abstract: The transport of deformable particles (TDPs) through porous media has been of considerable interest due to the multiple applications found in industrial and medical processes. The adequate design of these applications has been mainly achieved through experimental efforts, since TDPs through porous media are challenging to model because of the mechanical blockage of the pore throat due to size exclusion, deformation in order to pass through the pore throat under the driven pressure, and breakage under strong extrusion. In this work, based on the diffusivity equation and considering the TDP as a complex fluid whose viscosity and density depend on the local pressure, a simple but accurate theoretical model is proposed to describe the pressure behavior under steady- and unsteady-state flow conditions. Assuming a linear pressure dependence of the viscosity and density of the TDPs, valid for moderate pressure changes, the solution of the mathematical model yields a quantitative correlation between the pressure evolution and the parameters compressibility, viscosity coefficient, elastic modulus, particle size, and friction factor. The predictions of the model agree with experiments and allow the understanding of transport of deformable particles through a porous media.
Citation: Fluids
PubDate: 2024-11-22
DOI: 10.3390/fluids9120275
Issue No: Vol. 9, No. 12 (2024)
- Fluids, Vol. 9, Pages 276: Investigation of Nonlinear Relations Among Flow
Profiles Using Artificial Neural Networks
Authors: Shiming Yuan, Caixia Chen, Yong Yang, Yonghua Yan
First page: 276
Abstract: This study investigated the ability of artificial neural networks (ANNs) to resolve the nonlinear dynamics inherent in the behavior of complex fluid flows, which often exhibit multifaceted characteristics that challenge traditional analytical or numerical methods. By employing flow profile pairs that are generated through high-fidelity numerical simulations, encompassing both the one-dimensional benchmark problems and the more intricate three-dimensional boundary layer transition problem, this research convincingly demonstrates that neural networks possess a remarkable capacity to effectively capture the discontinuities and the subtle wave characteristics that occur at small scales within complex fluid flows, thereby showcasing their robustness in handling intricate fluid dynamics phenomena. Furthermore, even in the context of challenging three-dimensional problems, this study reveals that the average velocity profiles can be predicted with a high degree of accuracy, utilizing a limited number of input profiles during the training phase, which underscores the efficiency and efficacy of the model in understanding complex systems. The findings of this study significantly underscore the immense potential that artificial neural networks, along with deep learning methodologies, hold in advancing our comprehension of the fundamental physics that govern complex fluid dynamics systems, while concurrently demonstrating their applicability across a variety of flow scenarios and their capacity to yield insightful revelations regarding the nonlinear relationships that exist among diverse flow parameters, thus paving the way for future research in this critical area of study.
Citation: Fluids
PubDate: 2024-11-23
DOI: 10.3390/fluids9120276
Issue No: Vol. 9, No. 12 (2024)
- Fluids, Vol. 9, Pages 277: Impact of a Near-Surface Plasma Region on the
Bow Shock Wave and Aerodynamic Characteristics of a High-Speed Model in
Xenon
Authors: Olga A. Azarova, Tatiana A. Lapushkina, Oleg V. Kravchenko
First page: 277
Abstract: The main objective of this study is to demonstrate the active influence on the location of the bow shock wave, as well as on the parameters of an aerodynamic body, of a gas discharge organized near the frontal surface, between the body and the bow shock wave. The research is carried out using both experimental and numerical methods at the freestream Mach number M = 6.8. The working gas is xenon. It is shown that the location of the steady bow shock wave, along with the current and power of the discharge, is associated with the change in the adiabatic index of the plasma created by the discharge, which, in turn, is determined by plasma parameters such as the degrees of nonequilibrium and the degree of ionization. It is shown that the adiabatic index with the power supplied to the impact zone in the range of 30–120 kW can both increase and decrease in the range of 1.25–1.288. A study of the discharge-created plasma zone is conducted, and the correspondence between the gas discharge current and power and the average parameters in the plasma zone created by the discharge are presented. A good agreement between the numerical and experimental data is shown. The results obtained can be useful in the development of control systems for high-speed flows based not only on the effects of heating but also on the impact of plasma parameters.
Citation: Fluids
PubDate: 2024-11-23
DOI: 10.3390/fluids9120277
Issue No: Vol. 9, No. 12 (2024)
- Fluids, Vol. 9, Pages 278: The Potential of Machine Learning Methods for
Separated Turbulent Flow Simulations: Classical Versus Dynamic Methods
Authors: Stefan Heinz
First page: 278
Abstract: Feasible and reliable predictions of separated turbulent flows are a requirement to successfully address the majority of aerospace and wind energy problems. Existing computational approaches such as large eddy simulation (LES) or Reynolds-averaged Navier–Stokes (RANS) methods have suffered for decades from well-known computational cost and reliability issues in this regard. One very popular approach to dealing with these questions is the use of machine learning (ML) methods to enable improved RANS predictions. An alternative is the use of minimal error simulation methods (continuous eddy simulation (CES), which may be seen as a dynamic ML method) in the framework of partially or fully resolving simulation methods. Characteristic features of the two approaches are presented here by considering a variety of complex separated flow simulations. The conclusion is that minimal error CES methods perform clearly better than ML-RANS methods. Most importantly and in contrast to ML-RANS methods, CES is demonstrated to be well applicable to cases not involved in the model development. The reason for such superior CES performance is identified here: it is the ability of CES to properly account for causal relationships induced by the structure of separated turbulent flows.
Citation: Fluids
PubDate: 2024-11-25
DOI: 10.3390/fluids9120278
Issue No: Vol. 9, No. 12 (2024)
- Fluids, Vol. 9, Pages 279: Optimising Physics-Informed Neural Network
Solvers for Turbulence Modelling: A Study on Solver Constraints Against a
Data-Driven Approach
Authors: William Fox, Bharath Sharma, Jianhua Chen, Marco Castellani, Daniel M. Espino
First page: 279
Abstract: Physics-informed neural networks (PINNs) have emerged as a promising approach for simulating nonlinear physical systems, particularly in the field of fluid dynamics and turbulence modelling. Traditional turbulence models often rely on simplifying assumptions or closed numerical models, which simplify the flow, leading to inaccurate flow predictions or long solve times. This study examines solver constraints in a PINNs solver, aiming to generate an understanding of an optimal PINNs solver with reduced constraints compared with the numerically closed models used in traditional computational fluid dynamics (CFD). PINNs were implemented in a periodic hill flow case and compared with a simple data-driven approach to neural network modelling to show the limitations of a data-driven model on a small dataset (as is common in engineering design). A standard full equation PINNs model with predicted first-order stress terms was compared against reduced-boundary models and reduced-order models, with different levels of assumptions made about the flow to monitor the effect on the flow field predictions. The results in all cases showed good agreement against direct numerical simulation (DNS) data, with only boundary conditions provided for training as in numerical modelling. The efficacy of reduced-order models was shown using a continuity only model to accurately predict the flow fields within 0.147 and 2.6 percentage errors for streamwise and transverse velocities, respectively, and a modified mixing length model was used to show the effect of poor assumptions on the model, including poor convergence at the flow boundaries, despite a reduced solve time compared with a numerically closed equation set. The results agree with contemporary literature, indicating that physics-informed neural networks are a significant improvement in solve time compared with a data-driven approach, with a novel proposition of numerically derived unclosed equation sets being a good representation of a turbulent system. In conclusion, it is shown that numerically unclosed systems can be efficiently solved using reduced-order equation sets, potentially leading to a reduced compute requirement compared with traditional solver methods.
Citation: Fluids
PubDate: 2024-11-25
DOI: 10.3390/fluids9120279
Issue No: Vol. 9, No. 12 (2024)
- Fluids, Vol. 9, Pages 280: Hybrid CFD PINN FSI Simulation in Coronary
Artery Trees
Authors: Nursultan Alzhanov, Eddie Y. K. Ng, Yong Zhao
First page: 280
Abstract: This paper presents a novel hybrid approach that integrates computational fluid dynamics (CFD), physics-informed neural networks (PINN), and fluid–structure interaction (FSI) methods to simulate fluid flow in stenotic coronary artery trees and predict fractional flow reserve (FFR) in areas of stenosis. The primary objective is to utilize a 1D PINN model to accurately predict outlet flow conditions, effectively addressing the challenges of measuring or estimating these conditions within complex arterial networks. Validation against traditional CFD methods demonstrates strong accuracy while embedding physics-based training to ensure compliance with fundamental fluid dynamics principles. The findings indicate that the hybrid CFD PINN FSI method generates realistic outflow boundary conditions crucial for diagnosing stenosis, requiring minimal input data. By seamlessly integrating initial conditions established by the 1D PINN into FSI simulations, this approach enables precise assessments of blood flow dynamics and FFR values in stenotic regions. This innovative application of 1D PINN not only distinguishes this methodology from conventional data-driven models that rely heavily on extensive datasets but also highlights its potential to enhance our understanding of hemodynamics in pathological states. Ultimately, this research paves the way for significant advancements in non-invasive diagnostic techniques in cardiology, improving clinical decision making and patient outcomes.
Citation: Fluids
PubDate: 2024-11-25
DOI: 10.3390/fluids9120280
Issue No: Vol. 9, No. 12 (2024)
- Fluids, Vol. 9, Pages 281: Indoor Air Quality Control for Airborne
Diseases: A Review on Portable UV Air Purifiers
Authors: Shriram Sankurantripati, Florent Duchaine
First page: 281
Abstract: The spread of airborne diseases such as COVID-19 underscores the need for effective indoor air quality control. This review focuses on ventilation strategies and portable air purifiers as key mitigation solutions. Ventilation systems, including natural and mechanical approaches, can reduce pathogen concentrations by improving airflow. However, combining ventilation with portable air purifiers, particularly those using HEPA filters, ESP filters, and UV-C radiation, can enhance Indoor air quality. While HEPA and ESP filters focus on trapping airborne particles, UV-C radiation can inactivate pathogens by disrupting their RNA. A review of UV air purifiers reveals a lack of studies on their efficacy and effectiveness in real-world settings. A thorough investigation into the performance of this mitigation solution is necessary, focusing on varying key factors, such as purifier placement, airflow dynamics, and UV dosage, to ensure optimal effectiveness. High-fidelity computational methods are essential in accurately assessing these factors, as informed by the physics of airborne transmission. Such advanced computations are necessary to determine the viability of portable UV air purifiers in mitigating airborne transmission in enclosed environments such as hospitals and public spaces. Integrating advanced air purification technologies with proper ventilation can improve safety in indoor environments and prevent future disease-related outbreaks.
Citation: Fluids
PubDate: 2024-11-26
DOI: 10.3390/fluids9120281
Issue No: Vol. 9, No. 12 (2024)
- Fluids, Vol. 9, Pages 282: Experimental Investigation of Anisotropic
Invariants in Streams with Rigid Vegetation and 3D Bedforms
Authors: Kourosh Nosrati, Ali Rahm Rahimpour, Hossein Afzalimehr, Mohammad Nazari-Sharabian, Moses Karakouzian
First page: 282
Abstract: The presence of vegetation in submerged conditions and bedforms are a reality in coarse-bed streams. However, this reality has not been well investigated in the literature, despite being a major challenge for natural stream restoration. In order to control many unknown factors affecting prototype scale, this experimental study has been conducted in a laboratory flume, considering 3D bedforms. The results of this study show that 3D bedforms with submerged vegetation elements may change all estimations from 3D to 2D forms near the bed due to the change in roughness. This will change the classic determinations of resistance to flow and sediment transport via Reynolds stress and turbulent flow and may lead to more-affordable complex hydraulic process modeling.
Citation: Fluids
PubDate: 2024-11-28
DOI: 10.3390/fluids9120282
Issue No: Vol. 9, No. 12 (2024)
- Fluids, Vol. 9, Pages 283: Active Displacement of a Unique
Diatom–Ciliate Symbiotic Association
Authors: Yonara Garcia, Felipe M. Neves, Flavio R. Rusch, Leandro T. De La Cruz, Marina E. Wosniack, J. Rudi Strickler, Marcos G. E. da Luz, Rubens M. Lopes
First page: 283
Abstract: Adaptive movement in response to individual interactions represents a fundamental evolutionary solution found by both unicellular organisms and metazoans to avoid predators, search for resources or conspecifics for mating, and engage in other collaborative endeavors. Displacement processes are known to affect interspecific relationships, especially when linked to foraging strategies. Various displacement phenomena occur in marine plankton, ranging from the large-scale diel vertical migration of zooplankton to microscale interactions around microalgal cells. Among these symbiotic interactions, collaboration between the centric diatom Chaetoceros coarctatus and the peritrich ciliate Vorticella oceanica is widely known and has been recorded in several studies. Here, using 2D and 3D tracking records, we describe the movement patterns of the non-motile, chain-forming diatoms (C. coarctatus) carried by epibiotic ciliates (V. oceanica). The reported data on the Chaetoceros–Vorticella association illustrated the consortium’s ability to generate distinct motility patterns. We established that the currents generated by the attached ciliates, along with the variability in the contraction and relaxation of ciliate stalks in response to food concentration, resulted in three types of trajectories for the consortium. The characteristics of these distinct paths were determined using robust statistical methods, indicating that the different displacement behaviors allowed the consortium to adequately explore distributed resources and remain within the food-rich layers provided in the experimental containers. A simple mechanical–stochastic model was successfully applied to simulate the observed displacement patterns, further supporting the proposed mechanisms of collective response to the environment.
Citation: Fluids
PubDate: 2024-11-29
DOI: 10.3390/fluids9120283
Issue No: Vol. 9, No. 12 (2024)
- Fluids, Vol. 9, Pages 284: On the Numerical Investigation of Two-Phase
Evaporative Spray Cooling Technology for Data Centre Applications
Authors: Ning Gao, Syed Mughees Ali, Tim Persoons
First page: 284
Abstract: Two-phase evaporative spray cooling technology can significantly reduce power consumption in data centre cooling applications. However, the literature lacks an established methodology for assessing the overall performance of such evaporation systems in terms of the water-energy nexus. The current study develops a Lagrangian–Eulerian computational fluid dynamics (CFD) modelling approach to examine the functionality of these two-phase evaporative spray cooling systems. To replicate a modular system, a hollow spray cone nozzle with Rosin–Rammler droplet size distribution is simulated in a turbulent convective natural-air environment. The model was validated against the available experimental data from the literature. Parametric studies on geometric, flow, and climatic conditions, namely, domain length, droplet size, water mass flow rate, temperature, and humidity, were performed. The findings indicate that at elevated temperatures and low humidity, evaporation results in a bulk temperature reduction of up to 12 °C. A specific focus on the climatic conditions of Dublin, Ireland, was used as an example to optimize the evaporative system. A new formulation for the coefficient of performance (COP) is established to assess the performance of the system. Results showed that doubling the injector water mass flow rate improved the evaporated mass flow rate by 188% but reduced the evaporation percentage by 28%, thus reducing the COP. Doubling the domain length improved the temperature drop by 175% and increased the relative humidity by 160%, thus improving the COP. The COP of the evaporation system showed a systematic improvement with a reduction in the droplet size and the mass flow rate for a fixed domain length. The evaporated system COP improves by two orders of magnitude (~90 to 9500) with the reduction in spray Sauter mean diameter (SMD) from 292 μm to 8–15 μm. Under this reduction, close to 100% evaporation rate was achieved in comparison to only a 1% evaporation rate for the largest SMD. It was concluded that the utilization of a fine droplet spray nozzle provides an effective solution for the reduction in water consumption (97% in our case) for data centres, whilst concomitantly augmenting the proportion of evaporation.
Citation: Fluids
PubDate: 2024-11-29
DOI: 10.3390/fluids9120284
Issue No: Vol. 9, No. 12 (2024)
- Fluids, Vol. 9, Pages 285: The Bottleneck in the Scalar Dissipation Rate
Spectra: Dependence on the Schmidt Number
Authors: Paolo Orlandi
First page: 285
Abstract: The mean dissipation rate of turbulent energy reaches a constant value at high Taylor–Reynolds numbers (Rλ). This value is associated with the well-scaling dissipation spectrum in Kolmogorov units, where the maximum corresponds to the bottleneck peak. Even the scalar dissipation rate at the high Rλ considered in the present direct numerical simulations attains a constant value as Sc increases. In this scenario, the maximum of the scalar dissipation spectra reaches its peak within the bottleneck, starting at Sc>0.5. A qualitative explanation for the formation of the two bottlenecks is related to the blockage of energy transfer from large to small scales in the inertial ranges. Within the bottleneck, the self-similar, ribbon-like structures transition into the rod-like structures characteristic of the exponential decay range. Investigating the viscous dependence of the bottleneck’s amplitude may be aided by examining the evolution of a passive scalar. As Sc decreases, the scalar spectra undergo changes across the wave number k range. The bottleneck is dismantled, and at very low Sc values, the spectrum tends towards Batchelor’s theoretical prediction, diminishing proportionally to k−17/3. To comprehend the flow structures responsible for the bottleneck, visualizations of θ∇2θ and probability density functions at various Sc values are presented and compared with those of ui∇2ui. The numerical method employed for generating three-dimensional spectra and quantities such as energy and scalar variance dissipation in physical space must be accurate, particularly in resolving small scales. This paper additionally demonstrates that the second-order finite difference scheme conserving kinetic energy and scalar variance in the inviscid limit in viscous simulations accurately predicts the exponential decay range in one-dimensional and three-dimensional turbulent kinetic energy and scalar variance spectra.
Citation: Fluids
PubDate: 2024-12-04
DOI: 10.3390/fluids9120285
Issue No: Vol. 9, No. 12 (2024)
- Fluids, Vol. 9, Pages 286: Evaporation Dynamics and Dosimetry Methods in
Numerically Assessing MDI Performance in Pulmonary Drug Delivery
Authors: Mohamed Talaat, Xiuhua Si, Jinxiang Xi
First page: 286
Abstract: Metered dose inhalers (MDIs) play a crucial role in managing respiratory diseases, but their effectiveness depends on whether the intended dose is delivered to the target, which can be influenced by various factors. Accurate assessment of MDI performance is crucial for optimizing MDI delivery and ensuring drug efficacy. This study numerically examined the role of evaporation dynamics and dosimetry methods in assessing the efficiency of MDI delivery to different regions in a mouth–lung model extending to the eleventh generation (G11) of lung bifurcations. The experimentally determined spray exit speed, applied dose, and droplet size distribution were implemented as the initial/boundary conditions. Large eddy simulations (LES) were used to resolve the transient inhalation flows, and a chemical species model was applied to simulate vapor and temperature variations in the airflow. A multi-component model was used to consider the heat and mass transfer between the droplets and the airflow. The model was validated against literature data and applied to evaluate the impact of evaporation on pulmonary drug delivery using MDI, in comparison to inert particles. Three methods were used to quantify deposition, which were based on the droplet count, the droplet mass, and the drug carried by the droplets. The results demonstrate that evaporation notably alters the spray droplet size distribution and subsequent deposition patterns. Compared to inert particles, evaporation led to significantly more droplets ranging from 1–5 µm entering the pulmonary region. For a given region, large discrepancies were observed in the deposition fraction (DF) using different dosimetry methods. In the lower lung, the count-based DF (33.9%) and mass-based DF (2.4%) differed by more than one order of magnitude, while the drug-based DF fell between them (20.5%). This large difference highlights the need to include evaporation in predictive dosimetry, as well as to use the appropriate method to quantify the delivery efficiency of evaporating droplets.
Citation: Fluids
PubDate: 2024-12-05
DOI: 10.3390/fluids9120286
Issue No: Vol. 9, No. 12 (2024)
- Fluids, Vol. 9, Pages 287: Large Eddy Simulation (LES) of Hydrogen Jet
Flames and Finite Element Analysis of Thermal Barrier Coating
Authors: Alon Davidy
First page: 287
Abstract: A jet flame occurs when the release of flammable gas or liquid ignites, resulting in a long, intense, and highly directional flame. This type of fire is commonly associated with industrial incidents involving pipelines, storage tanks, and other pressurized equipment. Jet fires are a significant concern in the oil and gas industry due to the handling and processing of large volumes of flammable hydrocarbons under pressure. The new computational method presented here includes several aspects of hydrogen jet flame accidents and their mitigation: the CFD simulation of a hydrogen jet flame using the HyRAM code and Fire Dynamics Simulator (FDS) software 5.0 using a large eddy simulation (LES) turbulence model; the calculation of the gaseous mixture’s thermo-physical properties using the GASEQ thermochemical code; the calculation of convective and radiative heat fluxes using empirical correlation; and a heat transfer simulation on the pipe thermal barrier coating (TBC) using COMSOL Multiphysics software 4.2a during the heating phase. This method developed for the ceramic blanket was validated successfully against the previous experimental results obtained by Gravit et al. It was shown that a jet fire’s maximum temperature obtained using FDS software was similar to that obtained using GASEQ thermochemical software 0.79 and HyRAM software. The TBC’s surface temperature reached 1945 °C. The stainless steel’s maximal temperature reached 165.5 °C. There was a slight decrease in UTS at this temperature.
Citation: Fluids
PubDate: 2024-12-05
DOI: 10.3390/fluids9120287
Issue No: Vol. 9, No. 12 (2024)
- Fluids, Vol. 9, Pages 288: A Chamfered Anchor Impeller Design for Enhanced
Efficiency in Agitating Viscoplastic Fluids
Authors: Amine Benmoussa, José C. Páscoa
First page: 288
Abstract: In industrial mixing processes, impeller design, rotational speed, and mixing conditions play a crucial role in determining process efficiency, product quality, and energy consumption. Optimizing the performance of stirring systems for non-Newtonian fluids is essential for achieving better results. This study examines the hydrodynamic and thermal performance of stirring systems for viscoplastic fluids, utilizing close-clearance anchor impellers with chamfered angles of 22.5°, 45°, and 67.5° in cylindrical, flat-bottom and unbaffled vessels. Through a comprehensive comparative analysis between standard and chamfered impeller designs, the study evaluates their efficacy in overcoming yield stress, enhancing flow dynamics, and improving thermal homogeneity. The effects of Reynolds number and yield stress on the hydrodynamic and thermal states are analyzed. The results indicate that the 67.5° chamfered impeller significantly improves flow distribution and minimizes dead zones, particularly in critical areas between the anchor blades and vessel walls, where mixing stagnation typically occurs. It also enhances vertical mixing by promoting a broader shear spread along the vessel height and a more uniform temperature distribution. These insights contribute to the development of more efficient agitation systems, applicable across various industries handling complex fluids.
Citation: Fluids
PubDate: 2024-12-05
DOI: 10.3390/fluids9120288
Issue No: Vol. 9, No. 12 (2024)
- Fluids, Vol. 9, Pages 289: Simplified Approach to Evaluate Cavitation
Intensity Based on Time Information on Imposed Pressure in Liquid
Authors: Hiroyuki Kawashima, Hiroyuki Kogawa, Masatoshi Futakawa, Nobuatsu Tanaka
First page: 289
Abstract: Cavitation damage is an important research topic in fluid–structure interactions, such as those being studied using the mercury target for the pulsed neutron source at the Materials Life Science Experimental Facility/Japan Proton Accelerator Complex. Hence, the estimation of cavitation damage (cavitation intensity) is required from the perspective of structural integrity. The results of previous studies suggest that the maximum radii of cavitation bubbles immediately prior to collapse are related to cavitation intensity. Therefore, we propose a method for estimating the maximum radius from the time information by measuring the vibrations of structure walls that are induced by collapsing cavitation bubbles in a confined liquid. In this study, we used a magnetic impact testing machine to experimentally investigate the cavitation bubble dynamics, directly observe the bubble collapsing behavior, and measure the induced vibration. We experimentally confirmed that the time information is useful in the estimation of the maximum radii of bubbles. Moreover, we theoretically derived a simple evaluation formula to estimate the maximum radius from the time responses of the imposed pressure in a confined liquid in a structure.
Citation: Fluids
PubDate: 2024-12-06
DOI: 10.3390/fluids9120289
Issue No: Vol. 9, No. 12 (2024)
- Fluids, Vol. 9, Pages 290: Synthetic Jet Actuators for Active Flow
Control: A Review
Authors: Howard H. Ho, Ali Shirinzad, Ebenezer E. Essel, Pierre E. Sullivan
First page: 290
Abstract: A synthetic jet actuator (SJA) is a fluidic device often consisting of a vibrating diaphragm that alters the volume of a cavity to produce a synthesized jet through an orifice. The cyclic ingestion and expulsion of the working fluid leads to a zero-net mass-flux and the transfer of linear momentum to the working fluid over an actuation cycle, leaving a train of vortex structures propagating away from the orifice. SJAs are a promising technology for flow control applications due to their unique features, such as no external fluid supply or ducting requirements, short response time, low weight, and compactness. Hence, they have been the focus of many research studies over the past few decades. Despite these advantages, implementing an effective control scheme using SJAs is quite challenging due to the large parameter space involving several geometrical and operational variables. This article aims to explain the working mechanism of SJAs and provide a comprehensive review of the effects of SJA design parameters in quiescent conditions and cross-flow.
Citation: Fluids
PubDate: 2024-12-06
DOI: 10.3390/fluids9120290
Issue No: Vol. 9, No. 12 (2024)
- Fluids, Vol. 9, Pages 291: Interaction of the Shock Train Leading Edge and
Filamentary Plasma in a Supersonic Duct
Authors: Loren C. Hahn, Philip A. Lax, Scott C. Morris, Sergey B. Leonov
First page: 291
Abstract: Quasi-direct current (Q-DC) filamentary electrical discharges are used to control the shock train in a back-pressured Mach 2 duct flow. The coupled interaction between the plasma filaments and the shock train leading edge (STLE) is studied for a variety of boundary conditions. Electrical parameters associated with the discharge are recorded during actuation, demonstrating a close correlation between the STLE position and dynamics. High-speed self-aligned focusing schlieren (SAFS) and high frame-rate color camera imaging are the primary optical diagnostics used to study the flowfield and plasma morphology. Shock tracking and plasma characterization algorithms are employed to extract time-resolved quantitative data during shock–plasma interactions. Four distinct shock–plasma interaction types are identified and outlined, revealing a strong dependence on the spacing between the uncontrolled STLE and discharge electrodes and a moderate dependence on flow parameters.
Citation: Fluids
PubDate: 2024-12-07
DOI: 10.3390/fluids9120291
Issue No: Vol. 9, No. 12 (2024)
- Fluids, Vol. 9, Pages 292: Numerical Study of Laminar Unsteady Circular
and Square Jets in Crossflow in the Low Velocity Ratio Regime
Authors: Francisco C. Martins, José C. F. Pereira
First page: 292
Abstract: The unsteady three-dimensional flow interactions in the near field of square and circular jets issued normally to a crossflow were predicted by direct numerical simulations, aiming to investigate the effect of the nozzle cross-section on the vortical structures formed in this region. The analysis focuses on jets in crossflow with moderate Reynolds numbers (Rej=200 and Rej=300) based on the jet velocity the characteristic length of the nozzle and low jet-to-cross-flow velocity ratios, 0.25≤R≤1.4, where the jets are absolutely unstable. In this regime, the flow becomes periodic and laminar, and three distinct wake flow configurations were identified: (1) symmetric shedding of hairpin vortices at Rej=200; (2) the formation of toroidal vortices as the legs of hairpin vortices merge and the vortices roll up at Rej=300 and R≤0.67; (3) asymmetric shedding of hairpin vortices in the square jet at Rej=300 and R≥0.9, where higher-frequency hairpin vortex shedding combines with a low-frequency spanwise oscillation in the counter-rotating vortex pair. The dynamics of each of these flow states were analyzed. Power spectral density plots show a measurable increase in the shedding frequencies in Rej=300 jets with R, and that these frequencies are consistently larger in circular jets.
Citation: Fluids
PubDate: 2024-12-10
DOI: 10.3390/fluids9120292
Issue No: Vol. 9, No. 12 (2024)
- Fluids, Vol. 9, Pages 293: Features of Motion and Heat Transfer of
Swirling Flows in Channels of Complex Geometry
Authors: Sergey Dmitriev, Alexey Sobornov, Andrey Kurkin
First page: 293
Abstract: The computational and experimental study results of swirling single-phase coolant motion and heat transfer for the standard operation parameters of a nuclear power plant are presented. The experimental model is a vertical heat exchanger of a “pipe in a pipe” type with the countercurrent movement of coolants. Six different swirlers (three with a constant twist pitch and three with a variable pitch) were considered. The heat exchanger temperature field was measured at various combinations of coolant flow rates, and a channel pressure drop for each swirl was determined. Computational studies were performed using the Omega-based Reynolds stress model and SST model with a correction for curvature streamlines. A good agreement between numerical and experimental data was obtained. Based on the velocity and temperature fields, swirling flow motion features in channels with a variable swirl pitch were discovered. For each intensifier, the effectiveness criterion in comparison with a pipe channel was determined.
Citation: Fluids
PubDate: 2024-12-10
DOI: 10.3390/fluids9120293
Issue No: Vol. 9, No. 12 (2024)
- Fluids, Vol. 9, Pages 294: The Effect of Bifurcated Geometry on the
Diodicity of Tesla Valves
Authors: Sean Wiley, Huei-Ping Huang
First page: 294
Abstract: The Tesla valve is a fluidic diode that enables unidirectional flow while impeding the reverse flow without the assistance of any moving parts. Conventional Tesla valves share a distinctive feature of a bifurcated section that connects the inlet and outlet. This study uses computational fluid dynamic (CFD) simulations to analyze the importance of the bifurcated design to the efficiency of the Tesla valve, quantified by diodicity. Simulations over the range of the Reynolds number, Re = 50–2000, are performed for three designs: the T45-R, D-valve, and GMF valve, each with two versions with and without the bifurcated section. For the T45-R valve, removing the bifurcated section leads to a consistent increase in diodicity, particularly at high Re. In contrast, the diodicity of the GMF valve drops significantly when the bifurcated section is removed. The D-valve exhibits a mixed behavior. Without the bifurcated section, its diodicity is suppressed at low Re but begins to increase for Re > 1100, eventually matching the diodicity of the bifurcated version at Re = 2000. The results highlight the intricate relationship between valve geometry and efficiency of Tesla-type valves and the dependence of this relationship on the Reynolds number.
Citation: Fluids
PubDate: 2024-12-11
DOI: 10.3390/fluids9120294
Issue No: Vol. 9, No. 12 (2024)
- Fluids, Vol. 9, Pages 295: Two-Stage Multi-Objective Optimization for
Improving the Aerodynamic Characteristics of High-Speed Train Nose Shape
Authors: Suhwan Yun, Minho Kwak, Hyungmin Kang, Wonhee Park, Taesoo Kwon
First page: 295
Abstract: An optimal high-speed train nose design was formulated to reduce aerodynamic drag, mitigate tunnel micro-pressure waves, and improve crosswind safety. Using the vehicle modeling function, the EMU-320 nose shape was derived and applied as the base model for the optimal design. Following the initial optimization stage aimed at reducing aerodynamic drag, the second stage of optimization was conducted, using the results of the first stage as constraints, to further reduce tunnel micro-pressure waves and enhance crosswind safety. In the first stage, the aerodynamic drag was reduced by 8.7% due to the pointed nose shape. In the second stage, a Pareto front of optimal shapes was derived to reduce tunnel micro-pressure waves and improve crosswind safety, ensuring that the aerodynamic drag did not exceed the optimum achieved in the first stage by more than 1.5%. This two-stage multi-objective optimization is expected to be effectively utilized in the optimal design of high-speed train shapes that meet the intended purposes.
Citation: Fluids
PubDate: 2024-12-12
DOI: 10.3390/fluids9120295
Issue No: Vol. 9, No. 12 (2024)
- Fluids, Vol. 9, Pages 296: Investigating the Effects of Labeled Data on
Parameterized Physics-Informed Neural Networks for Surrogate Modeling:
Design Optimization for Drag Reduction over a Forward-Facing Step
Authors: Erik Gustafsson, Magnus Andersson
First page: 296
Abstract: Physics-informed neural networks (PINNs) are gaining traction as surrogate models for fluid dynamics problems, combining machine learning with physics-based constraints. This study investigates the impact of labeled data on the performance of parameterized physics-informed neural networks (PINNs) for surrogate modeling and design optimization. Different training approaches, including physics-only, data-only, and several combinations of both, are evaluated using fully connected (FCNN) and Fourier neural network (FNN) architectures. The test case focuses on reducing drag over a forward-facing step through optimal placement and sizing of an upstream obstacle. Results demonstrate that the inclusion of labeled data significantly enhances the accuracy and convergence rates of FCNNs, particularly in predicting flow separation and recirculation regions, and improves the stability of design optimization outcomes. Conversely, FNNs exhibit inconsistent responses to parameter changes when trained with labeled data, suggesting limitations in their applicability for certain design optimization tasks. The findings reveal that FCNNs trained with a balanced integration of data and physics constraints outperform both data-only and physics-only models, highlighting the importance of optimizing the training approach based on the specific requirements of fluid mechanics applications.
Citation: Fluids
PubDate: 2024-12-14
DOI: 10.3390/fluids9120296
Issue No: Vol. 9, No. 12 (2024)
- Fluids, Vol. 9, Pages 297: Effectiveness in Cooling a Heat Sink in the
Presence of a TPMS Porous Structure Comparing Two Different Flow
Directions
Authors: Mohamad Ziad Saghir, Mohammad M. Rahman
First page: 297
Abstract: The triply periodic minimal surface (TPMS) is receiving much interest among researchers. The advantage of using this TPMS structure is the ability to design a structure based on engineering need. In the present context, experimental measurement was conducted and compared with numerical models using a foam porous medium and TPMS porous structure, leading to an accurate calibration of the model. A porous medium, metal foam, was heated experimentally at the bottom, and forced convection was investigated for different heating conditions. Then, the porous foam was replaced with a TPMS, and the experiment was repeated under similar conditions. The experimental data were compared with the numerical model using COMSOL software. Besides the model’s accuracy, the TPMS showed a uniform heating condition contrary to the metal foam case. At a later stage, the numerical model was used to investigate the importance of flow direction (two flow directions) in cooling hot surfaces. The first flow was parallel to the hot surface, and the second perpendicular to the hot surface. The TPMS structure was located on the top of the hot surface and acted as a fin in both cases. The Nusselt number exceeded 80 in the presence of the TPMS. As the porosity of the TPMS decreases below 0.7, a more considerable pressure drop is observed. The performance evaluation criterion was found to be greater than 70 when the porosity of the TPMS structure was 0.8.
Citation: Fluids
PubDate: 2024-12-15
DOI: 10.3390/fluids9120297
Issue No: Vol. 9, No. 12 (2024)
- Fluids, Vol. 9, Pages 298: Combining CFD and AI/ML Modeling to Improve the
Performance of Polypropylene Fluidized Bed Reactors
Authors: Nayef Ghasem
First page: 298
Abstract: Polypropylene is one of the most widely used polymers in various applications, ranging from packaging materials to automotive components. This paper proposes the Computational Fluid Dynamics (CFD) and AI/ML simulation of a polypropylene fluidized bed reactor to reduce reactor loss and facilitate process understanding. COMSOL Multiphysics 6.2® solves a 2D multiphase CFD model for the reactor’s complex gas–solid interactions and fluid flows. The model is compared to experimental results and shows excellent predictions of gas distribution, fluid velocity, and temperature gradients. Critical operating parameters like feed temperature, catalyst feed rate, and propylene inlet concentration are all tested to determine their impact on the single-pass conversion of the reactor. The simulation simulates their effects on polypropylene yield and reactor efficiency. It also combines CFD with artificial intelligence and machine learning (AI/ML) algorithms, like artificial neural networks (ANN), resulting in a powerful predictive tool for accurately predicting reactor metrics based on operating conditions. The multifaceted CFD-AI/ML tool provides deep insight into improving reactor design, and it also helps save computing time and resources, giving industrial polypropylene plant growth a considerable lift.
Citation: Fluids
PubDate: 2024-12-16
DOI: 10.3390/fluids9120298
Issue No: Vol. 9, No. 12 (2024)
- Fluids, Vol. 9, Pages 299: The Reynolds Number: A Journey from Its Origin
to Modern Applications
Authors: Manuel Saldana, Sandra Gallegos, Edelmira Gálvez, Jonathan Castillo, Eleazar Salinas-Rodríguez, Eduardo Cerecedo-Sáenz, Juan Hernández-Ávila, Alessandro Navarra, Norman Toro
First page: 299
Abstract: The Reynolds number (Re), introduced in the late 19th century, has become a fundamental parameter in a lot of scientific fields—the main one being fluid mechanics—as it allows for the determination of flow characteristics by distinguishing between laminar and turbulent regimes, or some intermediate stage. Reynolds’ 1895 paper, which decomposed velocity into average and fluctuating components, laid the foundation for modern turbulence modeling. Since then, the concept has been applied to various fields, including external flows—the science that studies friction—as well as wear, lubrication, and heat transfer. Literature research in recent times has explored new interpretations of Re, and despite its apparent simplicity, the precise prediction of Reynolds numbers remains a computational challenge, especially under conditions such as the study of multiphase flows, non-Newtonian fluids, highly turbulent flow conditions, flows on very small scales or nanofluids, flows with complex geometries, transient or non-stationary flows, and flows of fluids with variable properties. Reynolds’ work, which encompasses both scientific and engineering contributions, continues to influence research and applications in fluid dynamics.
Citation: Fluids
PubDate: 2024-12-16
DOI: 10.3390/fluids9120299
Issue No: Vol. 9, No. 12 (2024)
- Fluids, Vol. 9, Pages 300: Reduced-Order Model of a Time-Trial Cyclist
Helmet for Aerodynamic Optimization Through Mesh Morphing and Enhanced
with Real-Time Interactive Visualization
Authors: E. Di Meo, A. Lopez, C. Groth, M. E. Biancolini, P. P. Valentini
First page: 300
Abstract: Aerodynamics is a key factor in time-trial cycling. Over the years, various aspects have been investigated, including positioning, clothing, bicycle design, and helmet shape. The present study focuses on the development of a methodology for the aerodynamic optimization of a time-trial helmet through the implementation of a reduced-order model, alongside advanced simulation techniques, such as computational fluid dynamics, radial basis functions, mesh morphing, and response surface methodology. The implementation of a reduced-order model enhances the understanding of aerodynamic interactions compared to traditional optimization workflows reported in sports-related research, facilitating the identification of an optimal helmet shape during the design phase. The study offers practical insights for refining helmet design. Starting with a baseline teardrop profile, several morphing configurations are systematically tested, resulting in a 10% reduction in the drag force acting on the helmet. The reduced-order model also facilitates the analysis of turbulent flow patterns on the cyclist’s body, providing a detailed understanding of aerodynamic interactions. By leveraging reduced-order models and advanced simulation techniques, this study contributes to ongoing efforts to reduce the aerodynamic resistance of time-trial helmets, ultimately supporting the goal of improved athlete performance.
Citation: Fluids
PubDate: 2024-12-17
DOI: 10.3390/fluids9120300
Issue No: Vol. 9, No. 12 (2024)
- Fluids, Vol. 9, Pages 301: Computational Modeling of Biomass Fast
Pyrolysis in Fluidized Beds with Eulerian Multifluid Approach
Authors: Cesar M. Venier, Erick Torres, Gastón G. Fouga, Rosa A. Rodriguez, Germán Mazza, Andres Reyes Urrutia
First page: 301
Abstract: This study investigated the fast pyrolysis of biomass in fluidized-bed reactors using computational fluid dynamics (CFD) with an Eulerian multifluid approach. A detailed analysis was conducted on the influence of various modeling parameters, including hydrodynamic models, heat transfer correlations, and chemical kinetics, on the product yield. The simulation framework integrated 2D and 3D geometrical setups, with numerical experiments performed using OpenFOAM v11 and ANSYS Fluent v18.1 for cross-validation. While yield predictions exhibited limited sensitivity to drag and thermal models (with differences of less than 3% across configurations and computational codes), the results underline the paramount role of chemical kinetics in determining the distribution of bio-oil (TAR), biochar (CHAR), and syngas (GAS). Simplified kinetic schemes consistently underestimated TAR yields by up to 20% and overestimated CHAR and GAS yields compared to experimental data (which is shown for different biomass compositions and different operating conditions) and can be significantly improved by redefining the reaction scheme. Refined kinetic parameters improved TAR yield predictions to within 5% of experimental values while reducing discrepancies in GAS and CHAR outputs. These findings underscore the necessity of precise kinetic modeling to enhance the predictive accuracy of pyrolysis simulations.
Citation: Fluids
PubDate: 2024-12-17
DOI: 10.3390/fluids9120301
Issue No: Vol. 9, No. 12 (2024)
- Fluids, Vol. 9, Pages 302: Study of Internal Flow in a Liquid Nitrogen
Flow Decelerator Through Swirl Effect Consisting of a Jet-Type Cryogenic
Injection System for Food Freezing
Authors: Ian Arriaga, Jasuo Sayán, Julio Ronceros, Mirko Klusmann, Renzo Albatrino, Carlos Raymundo, Gianpierre Zapata, Gustavo Ronceros
First page: 302
Abstract: This article addresses the study of internal flow dynamics within a cryogenic chamber designed for freezing food using liquid nitrogen injection. The chamber features a circular section with strategically placed jet-type atomizers for this purpose. The primary objective is to extend the residence time of the cryogenic fluid within the chamber to ensure uniform and effective freezing of the passing food items. This is achieved by inducing a swirl effect through strategic deceleration of the flow using the atomizers. The meticulous placement of these atomizers at periodic intervals along the internal walls of the cylindrical chamber ensures prolonged recirculation of the internal flow. Internal temperature analysis is crucial to ensure the freezing process. The study is supported by numerical analysis in CFD ANSYS to assess the dynamics of the swirl effect and parameters associated with the nitrogen–air interface, from which we obtain a sophisticated analysis thanks to the design of a hexahedral mesh made in greater detail in ICEM CFD. This approach aims to understand internal flow behavior and its correlation with the complexity of cryogenic system design, utilizing variable nitrogen-injection pressures and strategic atomizer placement as fundamental parameters to optimize system design.
Citation: Fluids
PubDate: 2024-12-17
DOI: 10.3390/fluids9120302
Issue No: Vol. 9, No. 12 (2024)
- Fluids, Vol. 9, Pages 303: Analysis of the Effect of Cut Sweep Ratio of
Lily Impeller on the Distribution of Dissolved Oxygen
Authors: Mohammad Tauviqirrahman, Eflita Yohana, Jourdy Cakranegara, Jamari, Budi Setiyana
First page: 303
Abstract: The aquaculture industry encounters substantial obstacles, including organic pollution, oxygen insufficiency, and elevated levels of ammonia and carbon dioxide. Aeration systems are employed to enhance the process of oxygen transfer and promote circulation. The Lily impeller, a newly developed technology, has demonstrated reduced energy consumption in comparison to conventional impeller designs. The objective of this study is to examine how changes in the cut sweep ratio impact the distribution of dissolved oxygen in shrimp ponds, using computational fluid dynamics (CFD) simulation. A user-defined function (UDF) was utilized to incorporate a dissolved oxygen model into the pond. Five designs of Lily impellers were analyzed and compared with each other. This study demonstrated that alterations in the cut sweep ratio significantly affected the distribution of dissolved oxygen, dynamic pressure, and flow velocity in the pond. The “no cut” variant exhibited the highest average dissolved oxygen value of 0.00385 kg/m3, along with a maximum dynamic pressure of 11.5 Pa and a maximum flow velocity of 0.96 m/s, resulting in the most significant outcomes. This study determined that only the immediate area surrounding the aerator possesses dissolved oxygen levels that are sufficiently elevated to support the survival of shrimp. Consequently, the installation of additional aerators is necessary to guarantee the presence of adequate dissolved oxygen throughout the entire pond.
Citation: Fluids
PubDate: 2024-12-19
DOI: 10.3390/fluids9120303
Issue No: Vol. 9, No. 12 (2024)
- Fluids, Vol. 9, Pages 245: Effects of Channelling a Peripherally Inserted
Central Venous Catheter on Blood Flow
Authors: Laura Hernández-Cabré, Marta Ulldemolins-Rams, Judit Vilanova-Corsellas, Carles Torras
First page: 245
Abstract: A catheter is a device that is inserted into the venous system to infuse treatment with controlled doses per unit of time. The study of its interaction with blood flow cannot be easily analysed with common analytical methods or different visualization techniques in real life. Computational Fluid Dynamics has become a very useful tool in a wide variety of fields of scientific study and has allowed access to the understanding of the anatomical and physiological functioning of the human body. In this work, Computational Fluid Dynamics is used to study the effects of inserting a catheter on blood flow and the quality of the mixture of blood with the various substances infused through this device. Results show that the insertion of the catheter not only does not worsen the blood circulation but improves it by reducing stagnant zones. Regarding mixture, a homogenization of the fluids in the venous area before their entrance to the heart was observed. Highest quality mixtures correspond to fewer infused fluids and at lower velocity.
Citation: Fluids
PubDate: 2024-10-22
DOI: 10.3390/fluids9110245
Issue No: Vol. 9, No. 11 (2024)
- Fluids, Vol. 9, Pages 246: Improved Delayed Detached-Eddy Simulation of
Turbulent Vortex Shedding in Inert Flow over a Triangular Bluff Body
Authors: Matthew R. McConnell, Jason Knight, James M. Buick
First page: 246
Abstract: The Improved Delayed Detached-Eddy Simulation (IDDES) is a modification of the original Detached-Eddy Simulation (DES) design to incorporate Wall Modeled Large Eddy Simulation (WMLES) capabilities and to extend the class of flows suitable for this methodology. For thin attached boundary layers, typically seen in external aerodynamic flows, the DES branch of the model is active, whereas with thick boundary layers, typically seen in internal flows and also wake flows, the WMLES branch is active, thus providing a numeric method suited to handling most flow cases automatically. The flow over a triangular bluff body is used to validate the suitability of the IDDES model and compare the results with experimental, DDES, and LES data. The IDDES model is found to be relatively accurate when compared with the experimental results, with recirculation length, streamwise velocity, and Reynolds stresses all showing good agreement with the experimental data. However, when compared with the DDES model, there is a ~4% overprediction of the recirculation length using the same mesh and numerical scheme. The code, with its extra complexity, is also ~3% slower to solve. The IDDES model has also been tested against different meshes, and the results show that even for a coarse mesh, there is still good agreement with the experimental data.
Citation: Fluids
PubDate: 2024-10-24
DOI: 10.3390/fluids9110246
Issue No: Vol. 9, No. 11 (2024)
- Fluids, Vol. 9, Pages 247: Prediction of Scour Depth for Diverse Pier
Shapes Utilizing Two-Dimensional Hydraulic Engineering Center’s
River Analysis System Sediment Model
Authors: Muhanad Al-Jubouri, Richard P. Ray, Ethar H. Abbas
First page: 247
Abstract: Examining scouring around bridge piers is crucial for ensuring water-related infrastructure’s long-term safety and stability. Accurate forecasting models are essential for addressing scour, especially in complex water systems where traditional methods fall short. This study investigates the application of the HEC-RAS 2D sedimentation model, which has recently become available for detailed sediment analysis, to evaluate its effectiveness in predicting scoring around various pier shapes and under different water conditions. This study offers a comprehensive assessment of the model’s predictive capabilities by focusing on variables such as water velocity, shear stress, and riverbed changes. Particular attention was paid to the influence of factors like floating debris and different pier geometries on scour predictions. The results demonstrate that while the HEC-RAS 2D model generally provides accurate predictions for simpler pier shapes—achieving up to 85% precision—it shows varied performance for more complex designs and debris-influenced scenarios. Specifically, the model overpredicted scouring depths by approximately 20% for diamond-shaped piers and underpredicted by 15% for square piers in debris conditions. Elliptical piers, in contrast, experienced significantly less erosion, with scour depths up to 30% shallower compared to other shapes. This study highlights the novel application of the HEC-RAS 2D model in this context and underscores its strengths and limitations. Identified issues include difficulties in modeling water flow and debris-induced bottlenecks. This research points to the improved calibration of sediment movement parameters and the development of advanced computational techniques to enhance scour prediction accuracy in complex environments. This work contributes valuable insights for future research and practical applications in civil engineering, especially where traditional scour mitigation methods, such as apron coverings, are not feasible.
Citation: Fluids
PubDate: 2024-10-25
DOI: 10.3390/fluids9110247
Issue No: Vol. 9, No. 11 (2024)
- Fluids, Vol. 9, Pages 248: On the Use of Different Sets of Variables for
Solving Unsteady Inviscid Flows with an Implicit Discontinuous Galerkin
Method
Authors: Luca Alberti, Emanuele Cammalleri, Emanuele Carnevali, Alessandra Nigro
First page: 248
Abstract: This article presents a comparison between the performance obtained by using a spatial discretization of the Euler equations based on a high-order discontinuous Galerkin (dG) method and different sets of variables. The sets of variables investigated are as follows: (1) conservative variables; (2) primitive variables based on pressure and temperature; (3) primitive variables based on the logarithms of pressure and temperature. The solution is advanced in time by using a linearly implicit high-order Rosenbrock-type scheme. The results obtained using the different sets are assessed across several canonical unsteady test cases, focusing on the accuracy, conservation properties and robustness of each discretization. In order to cover a wide range of physical flow conditions, the test-cases considered here are (1) the isentropic vortex convection, (2) the Kelvin–Helmholtz instability and (3) the Richtmyer–Meshkov instability.
Citation: Fluids
PubDate: 2024-10-25
DOI: 10.3390/fluids9110248
Issue No: Vol. 9, No. 11 (2024)
- Fluids, Vol. 9, Pages 249: Non-Spherical Cavitation Bubbles: A Review
Authors: Boxin Jia, Hitoshi Soyama
First page: 249
Abstract: Cavitation is a phase-change phenomenon from the liquid to the gas phase due to an increased flow velocity. As it causes severe erosion and noise, it is harmful to hydraulic machinery such as pumps, valves, and screw propellers. However, it can be utilized for water treatment, in chemical reactors, and as a mechanical surface treatment, as radicals and impacts at the point of cavitation bubble collapse can be utilized. Mechanical surface treatment using cavitation impacts is called “cavitation peening”. Cavitation peening causes less pollution because it uses water to treat the mechanical surface. In addition, cavitation peening improves on traditional methods in terms of fatigue strength and the working life of parts in the automobile, aerospace, and medical fields. As cavitation bubbles are utilized in cavitation peening, the study of cavitation bubbles has significant value in improving this new technique. To achieve this, many numerical analyses combined with field experiments have been carried out to measure the stress caused by bubble collapse and rebound, especially when collapse occurs near a solid boundary. Understanding the mechanics of bubble collapse can help to avoid unnecessary surface damage, enabling more accurate surface preparation, and improving the stability of cavitation peening. The present study introduces three cavitation bubble types: single, cloud, and vortex cavitation bubbles. In addition, the critical parameters, governing equations, and high-speed camera images of these three cavitation bubble types are introduced to support a broader understanding of the collapse mechanism and characteristics of cavitation bubbles. Then, the results of the numerical and experimental analyses of non-spherical cavitation bubbles are summarized.
Citation: Fluids
PubDate: 2024-10-25
DOI: 10.3390/fluids9110249
Issue No: Vol. 9, No. 11 (2024)
- Fluids, Vol. 9, Pages 250: A Nonlinear Approach in the Quantification of
Numerical Uncertainty by High-Order Methods for Compressible Turbulence
with Shocks
Authors: H. C. Yee, P. K. Sweby, Björn Sjögreen, D. V. Kotov
First page: 250
Abstract: This is a comprehensive overview on our research work to link interdisciplinary modeling and simulation techniques to improve the predictability and reliability simulations (PARs) of compressible turbulence with shock waves for general audiences who are not familiar with our nonlinear approach. This focused nonlinear approach is to integrate our “nonlinear dynamical approach” with our “newly developed high order entropy-conserving, momentum-conserving and kinetic energy-preserving methods” in the quantification of numerical uncertainty in highly nonlinear flow simulations. The central issue is that the solution space of discrete genuinely nonlinear systems is much larger than that of the corresponding genuinely nonlinear continuous systems, thus obtaining numerical solutions that might not be solutions of the continuous systems. Traditional uncertainty quantification (UQ) approaches in numerical simulations commonly employ linearized analysis that might not provide the true behavior of genuinely nonlinear physical fluid flows. Due to the rapid development of high-performance computing, the last two decades have been an era when computation is ahead of analysis and when very large-scale practical computations are increasingly used in poorly understood multiscale data-limited complex nonlinear physical problems and non-traditional fields. This is compounded by the fact that the numerical schemes used in production computational fluid dynamics (CFD) computer codes often do not take into consideration the genuinely nonlinear behavior of numerical methods for more realistic modeling and simulations. Often, the numerical methods used might have been developed for weakly nonlinear flow or different flow types other than the flow being investigated. In addition, some of these methods are not discretely physics-preserving (structure-preserving); this includes but is not limited to entropy-conserving, momentum-conserving and kinetic energy-preserving methods. Employing theories of nonlinear dynamics to guide the construction of more appropriate, stable and accurate numerical methods could help, e.g., (a) delineate solutions of the discretized counterparts but not solutions of the governing equations; (b) prevent numerical chaos or numerical “turbulence” leading to FALSE predication of transition to turbulence; (c) provide more reliable numerical simulations of nonlinear fluid dynamical systems, especially by direct numerical simulations (DNS), large eddy simulations (LES) and implicit large eddy simulations (ILES) simulations; and (d) prevent incorrect computed shock speeds for problems containing stiff nonlinear source terms, if present. For computation intensive turbulent flows, the desirable methods should also be efficient and exhibit scalable parallelism for current high-performance computing. Selected numerical examples to illustrate the genuinely nonlinear behavior of numerical methods and our integrated approach to improve PARs are included.
Citation: Fluids
PubDate: 2024-10-25
DOI: 10.3390/fluids9110250
Issue No: Vol. 9, No. 11 (2024)
- Fluids, Vol. 9, Pages 251: A Review of Comprehensive Guidelines for
Computational Fluid Dynamics (CFD) Validation in Solar Chimney Power
Plants: Methodology and Manzanares Prototype Case Study
Authors: Saïf ed-Dîn Fertahi, Shafiqur Rehman, Khadija Lahrech, Abderrahim Samaouali, Asmae Arbaoui, Imad Kadiri, Rachid Agounoun
First page: 251
Abstract: This review provides a comprehensive examination of CFD modeling procedures for SCPP, with an emphasis on the detailed methodologies and a case study of the Manzanares prototype in Spain. The introduction delineates the historical context and physical modeling principles of solar chimneys, while highlighting their potential in industrial applications. The governing equations are meticulously discussed, covering assumptions in both 2D and 3D CFD modeling, the continuity and momentum equations, and the selection and accuracy of turbulence models, particularly the k-ε equations. The review also delves into heat transfer modeling, encompassing the energy equation and radiation modeling. Analytical evaluations of turbine pressure drop ratios and performance metrics for power generation efficiency are critically analyzed. The establishment of boundary conditions in solar chimney applications, including sky temperature assessments and distinctions between 2D and 3D boundary conditions, is extensively explored. Mesh generation techniques for both 2D and 3D CFD models are presented, supported by case studies. Parametric studies and experimental investigations are scrutinized to elucidate their impact on the performance of solar chimneys. The temperature–entropy diagram for an idealized Brayton cycle is introduced as a conceptual framework for efficiency analysis. Validation of the CFD codes, both 2D and 3D, against experimental data is performed to ensure model accuracy. The review further examines energy balance approaches in modeling solar chimneys, presenting state-of-the-art CFD results and discussing their implications in both 2D and 3D contexts. The synthesis of these findings culminates in a comprehensive conclusion, offering insights into the future directions and potential advancements in the CFD modeling of solar chimneys. This work aims to serve as a definitive reference for researchers and practitioners in the field, providing a robust foundation for the development and optimization of SCPP technology.
Citation: Fluids
PubDate: 2024-10-27
DOI: 10.3390/fluids9110251
Issue No: Vol. 9, No. 11 (2024)
- Fluids, Vol. 9, Pages 252: On the Numerical Investigation of
Natural-Convection Heat Sinks Across a Wide Range of Flow and Operating
Conditions
Authors: Louis Dewilde, Syed Mughees Ali, Rajesh Nimmagadda, Tim Persoons
First page: 252
Abstract: Many designs for natural-convection heat sinks and semi-empirical correlations have been proposed in the recent years, but they are only valid in a limited range of Elenbaas numbers El and were mostly tested for laminar flows. To alleviate those limits, parametric studies with 2D and quasi-3D models were carried out, in ranges of Grashof numbers up to 1.55×1011 and Elenbaas numbers up to 3.42×107. Ansys Fluent’s laminar, transition-SST, SST k-ω and k-ϵ models were applied. In addition, when used in this valid range, i.e., mean Elenbaas numbers, with the simplified quasi-3D model, the transition-SST model could predict better results, overestimating the heat flux by 10 to 15% compared to semi-empirical correlations. The 2D model was not deemed satisfying, regarding turbulence models. Consequently, a quasi-3D model was developed: it appeared to be an efficient trade-off between computational time and prediction accuracy, in particular for turbulence models. New grouping factors were also found, to ensure proper dimensioning of natural-convection heat sinks. They corresponded to non-dimensional parameters that dictated the physical behaviour of the heat sink with respect to the semi-empirical correlations. Typically, the ratio of the spacing to the optimal spacing predicted by Bar-Cohen’s correlation turned out to be an appropriate grouping factor with a threshold of 1, above which the fins could safely be considered as isolated, thus greatly simplifying all further calculations.
Citation: Fluids
PubDate: 2024-10-28
DOI: 10.3390/fluids9110252
Issue No: Vol. 9, No. 11 (2024)
- Fluids, Vol. 9, Pages 253: Passive Control of the Flow Around a
Rectangular Cylinder with a Custom Rough Surface
Authors: Mario A. Aguirre-López, Filiberto Hueyotl-Zahuantitla, Pedro Martínez-Vázquez, José Ulises Márquez-Urbina
First page: 253
Abstract: Motivated by existing techniques for implementing roughness on cylinders to control flow disturbances, we performed delayed detached eddy simulations (DDES) at Re = 6×106 that generated unsteady turbulent flow around a rectangular cylinder with a controlled wrinkled surface and a 1:4 aspect ratio. A systematic study of the roughness effect was carried out by implementing different configurations of equally spaced grooves and bumps on the top-surface of the cylinder. Our results suggest that groove geometries reduce energy dissipation at higher rates than the smooth reference case, whereas bumped cylinders produce relative pressures characterized by a sawtooth pattern along the middle-upper part of the cylinder. Moreover, cylinders with triangular bumps increase mean drag and lift forces by up to 8% and 0.08 units, respectively, while circular bumps increase vorticity and pressure disturbances on the wrinkled surface. All of these effects impact energy dissipation, vorticity, pressure coefficients, and flow velocity along the wrinkled surface. Both the surface-manufactured cylinders and the proposed visualization techniques could be replicated in a variety of engineering developments involving flow characterization in the presence of roughness.
Citation: Fluids
PubDate: 2024-10-29
DOI: 10.3390/fluids9110253
Issue No: Vol. 9, No. 11 (2024)
- Fluids, Vol. 9, Pages 254: A Review of Biomechanical Studies of Heart
Valve Flutter
Authors: Lu Chen, Zhuo Zhang, Tao Li, Yu Chen
First page: 254
Abstract: This paper reviews recent biomechanical studies on heart valve flutter. The function of the heart valves is essential for maintaining effective blood circulation. Heart valve flutter is a kind of small vibration phenomenon like a flag fluttering in the wind, which is related to many factors such as a thrombus, valve calcification, regurgitation, and hemolysis and material fatigue. This vibration phenomenon is particularly prevalent in valve replacement patients. The biomechanical implications of flutter are profound and can lead to micro-trauma of valve tissue, accelerating its degeneration process and increasing the risk of thrombosis. We conducted a systematic review along with a critical appraisal of published studies on heart valve flutter. In this review, we summarize and analyze the existing literature; discuss the detection methods of frequency and amplitude of heart valve flutter, and its potential effects on valve function, such as thrombosis and valve degeneration; and discuss some possible ways to avoid flutter. These findings are important for optimizing valve design, diagnosing diseases, and developing treatment strategies.
Citation: Fluids
PubDate: 2024-10-29
DOI: 10.3390/fluids9110254
Issue No: Vol. 9, No. 11 (2024)
- Fluids, Vol. 9, Pages 255: Fokker-Planck Central Moment Lattice Boltzmann
Method for Effective Simulations of Fluid Dynamics
Authors: William Schupbach, Kannan Premnath
First page: 255
Abstract: We present a new formulation of the central moment lattice Boltzmann (LB) method based on a minimal continuous Fokker-Planck (FP) kinetic model, originally proposed for stochastic diffusive-drift processes (e.g., Brownian dynamics), by adapting it as a collision model for the continuous Boltzmann equation (CBE) for fluid dynamics. The FP collision model has several desirable properties, including its ability to preserve the quadratic nonlinearity of the CBE, unlike that based on the common Bhatnagar-Gross-Krook model. Rather than using an equivalent Langevin equation as a proxy, we construct our approach by directly matching the changes in different discrete central moments independently supported by the lattice under collision to those given by the CBE under the FP-guided collision model. This can be interpreted as a new path for the collision process in terms of the relaxation of the various central moments to “equilibria”, which we term as the Markovian central moment attractors that depend on the products of the adjacent lower order moments and a diffusion coefficient tensor, thereby involving of a chain of attractors; effectively, the latter are nonlinear functions of not only the hydrodynamic variables, but also the non-conserved moments; the relaxation rates are based on scaling the drift coefficient by the order of the moment involved. The construction of the method in terms of the relevant central moments rather than via the drift and diffusion of the distribution functions directly in the velocity space facilitates its numerical implementation and analysis. We show its consistency to the Navier-Stokes equations via a Chapman-Enskog analysis and elucidate the choice of the diffusion coefficient based on the second order moments in accurately representing flows at relatively low viscosities or high Reynolds numbers. We will demonstrate the accuracy and robustness of our new central moment FP-LB formulation, termed as the FPC-LBM, using the D3Q27 lattice for simulations of a variety of flows, including wall-bounded turbulent flows. We show that the FPC-LBM is more stable than other existing LB schemes based on central moments, while avoiding numerical hyperviscosity effects in flow simulations at relatively very low physical fluid viscosities through a refinement to a model founded on kinetic theory.
Citation: Fluids
PubDate: 2024-10-29
DOI: 10.3390/fluids9110255
Issue No: Vol. 9, No. 11 (2024)
- Fluids, Vol. 9, Pages 256: Adaptive Free-Form Deformation Parameterization
Based on Spring Analogy Method for Aerodynamic Shape Optimization
Authors: Jinxin Zhou, Xiaojun Wu, Hongyin Jia, Jing Yu
First page: 256
Abstract: An adaptive Free-Form Deformation parameterization method based on a spring analogy is presented for aerodynamic shape optimization problems. The proposed method effectively incorporates the gradients of the objective and constraint functions, achieving automatic control point adjustment based on variances in design variable components. To evaluate the performance of the adaptive FFD parameterization method, two 2D airfoil optimization design problems are examined. The optimization of the RAE2822 airfoil with 12, 18 and 24 design variables demonstrates superior results for the adaptive method compared to uniform parameterization. The adaptive method requires fewer iterations and achieves lower objective function values. Additionally, the optimization design from NACA0012 to RAE2822 airfoil with 18 design variables shows that the adaptive parameterization method achieves a lower drag coefficient while satisfying the optimization objective. This validates the method’s capability to finely adjust airfoil shapes and capture more optimal design points by exerting stronger control over local shapes. The proposed adaptive FFD parameterization method proves highly effective for optimizing aerodynamic shapes, offering stability and efficiency in the early stages of optimization, even with a limited number of design variables.
Citation: Fluids
PubDate: 2024-10-31
DOI: 10.3390/fluids9110256
Issue No: Vol. 9, No. 11 (2024)
- Fluids, Vol. 9, Pages 257: Multi-Objective Numerical Analysis of
Horizontal Rectilinear Earth–Air Heat Exchangers with Elliptical
Cross Section Using Constructal Design and TOPSIS
Authors: Ivanilton Reinato de Andrade, Elizaldo Domingues dos Santos, Houlei Zhang, Luiz Alberto Oliveira Rocha, Andre Luis Razera, Liércio André Isoldi
First page: 257
Abstract: This study presents a numerical evaluation of a Horizontal Rectilinear Earth–air Heat Exchanger (EAHE), considering the climatic and soil conditions of Viamão, Brazil, a subtropical region. The Constructal Design method, combined with the Exhaustive Search, was utilized to define the system constraints, degree of freedom, and performance indicators. The degree of freedom was characterized by the aspect ratio between the vertical and horizontal lengths of the elliptical cross-section duct (H/L). The performance indicators for the EAHE configurations were assessed based on thermal potential (TP) and pressure drop (PD). The Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) was applied for multi-objective evaluation, and a methodology for EAHE is proposed. The problem was solved using FLUENT software (version 2024 R2), which employs the Finite Volume Method to solve the conservation equations for mass, momentum, and energy. The (H/L)T,o = 6.0 configuration showed a 16.4% increase in thermal performance for heating and 15.9% for cooling compared to the conventional circular duct. Conversely, the (H/L)F,o = 1.0 configuration reduced pressure loss by 65.33%. The integration of Constructal Design with TOPSIS facilitated the identification of optimized geometries that achieve a balance between performance indicators and those that specifically prioritize thermal or fluid dynamic aspects, being this approach an original scientific contribution of the present work.
Citation: Fluids
PubDate: 2024-10-31
DOI: 10.3390/fluids9110257
Issue No: Vol. 9, No. 11 (2024)
- Fluids, Vol. 9, Pages 258: Fourier Neural Operator Networks for Solving
Reaction–Diffusion Equations
Authors: Yaobin Hao, Fangying Song
First page: 258
Abstract: In this paper, we used Fourier Neural Operator (FNO) networks to solve reaction–diffusion equations. The FNO is a novel framework designed to solve partial differential equations by learning mappings between infinite-dimensional functional spaces. We applied the FNO to the Surface Quasi-Geostrophic (SQG) equation, and we tested the model with two significantly different initial conditions: Vortex Initial Conditions and Sinusoidal Initial Conditions. Furthermore, we explored the generalization ability of the model by evaluating its performance when trained on Vortex Initial Conditions and applied to Sinusoidal Initial Conditions. Additionally, we investigated the modes (frequency parameters) used during training, analyzing their impact on the experimental results, and we determined the most suitable modes for this study. Next, we conducted experiments on the number of convolutional layers. The results showed that the performance of the models did not differ significantly when using two, three, or four layers, with the performance of two or three layers even slightly surpassing that of four layers. However, as the number of layers increased to five, the performance improved significantly. Beyond 10 layers, overfitting became evident. Based on these observations, we selected the optimal number of layers to ensure the best model performance. Given the autoregressive nature of the FNO, we also applied it to solve the Gray–Scott (GS) model, analyzing the impact of different input time steps on the performance of the model during recursive solving. The results indicated that the FNO requires sufficient information to capture the long-term evolution of the equations. However, compared to traditional methods, the FNO offers a significant advantage by requiring almost no additional computation time when predicting with new initial conditions.
Citation: Fluids
PubDate: 2024-11-06
DOI: 10.3390/fluids9110258
Issue No: Vol. 9, No. 11 (2024)
- Fluids, Vol. 9, Pages 259: Assessment of Cavitation Erosion Using Combined
Numerical and Experimental Approach
Authors: Milan Sedlář, Alois Koutný, Tomáš Krátký, Martin Komárek, Martin Fulín
First page: 259
Abstract: This paper aims to numerically assess the cavitation damage of hydrodynamic machines and hydraulic components and its development in time, based on cavitation erosion tests with samples of used materials. The theoretical part of this paper is devoted to the numerical simulation of unsteady multiphase flow by means of computational fluid dynamics (CFD) and to the prediction of the erosive effects of the collapses of cavitation bubbles in the vicinity of solid surfaces. Compressible unsteady Reynolds-averaged Navier–Stokes equations (URANS) are solved together with the Zwart cavitation model. To describe the destructive collapses of vapor bubbles, the modeling of cavitation bubble dynamics along selected streamlines or trajectories is applied. The hybrid Euler–Lagrange approach with one-way coupling and the full Rayleigh–Plesset equation (R–P) are therefore utilized. This paper also describes the experimental apparatus with a rotating disc used to reach genuine hydrodynamic cavitation and conditions similar to those of hydrodynamic machines. The simulations are compared with the obtained experimental data, with good agreement. The proposed methodology enables the application of the results of erosion tests to the real geometry of hydraulic machines and to reliably predict the locations and magnitude of cavitation erosion, so as to select appropriate materials or material treatments for endangered parts.
Citation: Fluids
PubDate: 2024-11-07
DOI: 10.3390/fluids9110259
Issue No: Vol. 9, No. 11 (2024)
- Fluids, Vol. 9, Pages 260: The Resistance of an Arbitrary Body in Confined
Unsteady Stokes Flow
Authors: Giuseppe Procopio, Valentina Biagioni, Massimiliano Giona
First page: 260
Abstract: In this article, we address resistance forces and torques acting onto a body with arbitrary shape moving in an unsteady Stokes flow. We start analyzing the functional form of the expressions for forces and torques, which depend on the frequency parameter and on the position of the body in the domain of the fluid, and determining the asymptotic limits for high and low frequencies. In this regard, we show that, for high frequencies (hence short times), forces and torques are obtained by the associated hydrodynamic problems considering ideal potential flows, independently of the geometry of the problem. Afterwards, with the aim of obtaining expressions for forces and torques valid in the entire range of frequencies, we extend to the unsteady case the reflection method, largely employed in the theory of the steady Stokes flows. In this way, general expressions are provided in terms of the Faxén operators of the body and the Green function associated with the geometry of the confinement, that are valid, to the leading order, at any frequency, independently of the geometry of the problem. Finally, as the application of the general expressions, explicit relations for the resistance forces acting onto a spherical body with no-slip boundary conditions near a plane wall with full-slip boundary conditions are obtained, valid over the entire frequency range, provided that the distance between the plane and the sphere is larger than one sphere radius.
Citation: Fluids
PubDate: 2024-11-07
DOI: 10.3390/fluids9110260
Issue No: Vol. 9, No. 11 (2024)
- Fluids, Vol. 9, Pages 261: Thermophysical Properties of Silicon Oxide
Nanoparticles in Water and Ethylene Glycol–Water Dispersions
Authors: Franz Wittmann, Zlatan Arnautovic, Florian Heberle, Dieter Brüggemann
First page: 261
Abstract: Measurements of transmission as well as thermophysical properties have been carried out for different concentrations of SiO2 nanoparticles (0, 1, 2, 5, 10, and 20 wt.%) in pure water (W) and ethylene glycol–water mixture (EG/W) in a weight ratio of 25/75, from 298 to 323 K at 100 kPa. In particular, the density, specific heat capacity, and thermal diffusivity are measured by a density meter, differential scanning calorimetry, and the laser flash method. In the case of 20 wt.% SiO2, transmission in the visible range is reduced by 9.3%. Simultaneously, the density rises linearly to 12.3% (in W) and 11.3% (in EG/W). The specific heat capacity decreases to 15.9% (in W) and 17.3% (in EG/W), while the thermal diffusivity rises to 16.4% (in W) and 20.4% (in EG/W). While the density measurements are in very good agreement with the literature, the measured values of the specific heat capacity deviate more than 5%, especially for concentrations below 5 wt.% SiO2. Moreover, it is shown that the thermal conductivity increases less for fluids in small gaps compared to other authors, which could be due to the suppression of the Brownian motion. Based on the measurement results, temperature- and concentration-dependent correlations for the investigated thermophysical properties are developed using two adjustable parameters. In general, these correlations show deviations of less than 4% from the experimental results, which will help to fill the gaps in the variation of experimental results due to size, SiO2 nanofluid production, and different measurement devices, and thus optimize solar thermal applications with SiO2 nanofluid.
Citation: Fluids
PubDate: 2024-11-08
DOI: 10.3390/fluids9110261
Issue No: Vol. 9, No. 11 (2024)
- Fluids, Vol. 9, Pages 262: Numerical Optimization of Drucker-Prager-Cap
Authors: Sanaz Davarpanah, Madjid Allili, Seyed Soheil Mousavi Ajarostaghi
First page: 262
Abstract: A growing number of scholars are drawn to using numerical approaches powered by computer simulations as a potential solution to industrial problems. Replicating the compaction process in powder metallurgy with accuracy is one such issue. The Drucker-Prager-Cap model requires parameter calibration as the most used method for simulating powder compaction. This paper addresses this issue and presents a new technique for doing so. Utilizing Abaqus software 2020, the compaction process was simulated for the benchmark powder, which is the alloy Ag57.6-Cu22.4-Sn10-In10. The difference between simulation results and experimental data was reduced by applying the Particle Swarm Optimization technique in Python. The suggested approach may accurately forecast the Drucker-Prager-Cap model parameters, as demonstrated by comparing the optimized parameters utilizing the research’s method with their experimental values. The findings revealed how well the suggested approach in this study calibrated the DPC model, yielding three parameters—Young’s modulus, material cohesion, and hydrostatic pressure yield stress—with respective RMSEs of 1.95, 0.12, and 324.64 concerning their experimental values.
Citation: Fluids
PubDate: 2024-11-10
DOI: 10.3390/fluids9110262
Issue No: Vol. 9, No. 11 (2024)
- Fluids, Vol. 9, Pages 263: Influence of Self-Heating on Landfill Leachate
Migration
Authors: Yanina Parshakova, Ruslan Kataev, Natalya Kartavykh, Mikhail Viskov, Andrey Ivantsov
First page: 263
Abstract: The hydrodynamic processes of landfill leachate migration in the base of a solid waste landfill can have a critical impact on the natural environment. In the case of improper operation of municipal solid waste placement facilities, highly contaminated leachate may penetrate into groundwater and subsequently into surface water. This work addresses fundamental issues of multicomponent fluid propagation in a multilayer porous medium, taking into account temperature inhomogeneities caused by waste decomposition with heat release. The regimes of diffusion and convection of leachate water penetrating into soil layers in the base of municipal solid waste facilities are numerically studied. Archival data from a set of field and laboratory measurements in the area of the operating landfill are used to model the features of pollutant propagation and determine migration parameters. The process of pollutant propagation and migration is described by quantitative values of dry residue content in leachate. Factors that have a significant impact on the migration of leachate are considered. The main ones are convective transfer, diffusion, and properties of the geological composition of the landfill base, which are taken into account in the mathematical formulation of the problem. The calculations show that leachate self-heating can substantially intensify leachate filtration and has to be taken into account in the assessment of leachate migration rate.
Citation: Fluids
PubDate: 2024-11-10
DOI: 10.3390/fluids9110263
Issue No: Vol. 9, No. 11 (2024)
- Fluids, Vol. 9, Pages 264: Investigating the Morphology of a Free-Falling
Jet with an Accurate Finite Element and Level Set Modeling
Authors: Yiming Liu, Hua Yang, Bilen Emek Abali, Wolfgang H. Müller
First page: 264
Abstract: This study investigates the morphology of a free-falling liquid jet by using a computational approach with an experimental validation. Numerical simulations are developed by means of the Finite Element Method (FEM) for solving the viscous fluid flow and the level set method in order to track the interface between the fluid and air. Experiments are conducted in order to capture the shape of a free-falling jet of viscous fluid via circular orifice, where the shape is measured optically. The numerical results are found to be in agreement with the experimental data, demonstrating the validity of the proposed approach. Furthermore, we analyze the role of the surface tension by implementing linear as well as nonlinear surface energy models. All computational codes are developed with the aid of open-source packages from FEniCS and made publicly available. The combination of experimental and numerical techniques provides a comprehensive understanding of the morphology of free-falling jets and may be extended to multiphysics problems rather in a straightforward manner.
Citation: Fluids
PubDate: 2024-11-10
DOI: 10.3390/fluids9110264
Issue No: Vol. 9, No. 11 (2024)
- Fluids, Vol. 9, Pages 265: Pollutant Dispersion Dynamics Under Horizontal
Wind Shear Conditions: Insights from Bidimensional Traffic Flow Models
Authors: Anis Chaari, Waleed Mouhali, Nacer Sellila, Mohammed Louaked, Houari Mechkour
First page: 265
Abstract: Meteorological factors, specifically wind direction and magnitude, influence the dispersion of atmospheric pollutants due to road traffic by affecting their spatial and temporal distribution. In this study, we are interested in the effect of the evolution of horizontal wind components, i.e., in the plane perpendicular to the altitude axis. A two-dimensional numerical model for solving the coupled traffic flow/pollution problem, whose pollutants are generated by vehicles, is developed. The numerical solution of this model is computed via an algorithm combining the characteristics method for temporal discretization with the finite-element method for spatial discretization. The numerical model is validated through a sensitivity study on the diffusion coefficient of road traffic and its impact on traffic density. The distribution of pollutant concentration, computed based on a source generated by traffic density, is presented for a single direction and different magnitudes of the wind velocity (stationary, Gaussian, linearly increasing and decreasing, sudden change over time), taking into account the stretching and tilting of plumes and patterns. The temporal evolution of pollutant concentration at various relevant locations in the domain is studied for two wind velocities (stationary and sudden change). Three regimes were observed for transport pollution depending on time and velocity: nonlinear growth, saturation, and decrease.
Citation: Fluids
PubDate: 2024-11-14
DOI: 10.3390/fluids9110265
Issue No: Vol. 9, No. 11 (2024)
- Fluids, Vol. 9, Pages 266: An Analysis and Comparison of the Hydrodynamic
Behavior of Ships Using Mesh-Based and Meshless Computational Fluid
Dynamics Simulations
Authors: Davide Caccavaro, Bonaventura Tagliafierro, Gianluca Bilotta, José M. Domínguez, Alessio Caravella, Roberto Gaudio, Alfredo Cassano, Corrado Altomare, Agostino Lauria
First page: 266
Abstract: This paper presents a comparison of two turbulence models implemented in two different frameworks (Eulerian and Lagrangian) in order to simulate the motion in calm water of a displacement hull. The hydrodynamic resistance is calculated using two open-source Computational Fluid Dynamics (CFD) software packages: OpenFOAM and DualSPHysics. These two packages are employed with two different numerical treatments to introduce turbulence closure effects. The methodology includes rigorous validation using a Wigley hull with experimental data taken from the literature. Then, the validated frameworks are applied to model a ship hull with a 30 m length overall (LOA), and their results discussed, outlining the advantages and disadvantages of the two turbulence treatments. In conclusion, the resistance calculated with OpenFOAM offers the best compactness of results and a shorter simulation time, whereas DualSPHysics can better capture the free-surface deformations, preserving similar accuracy.
Citation: Fluids
PubDate: 2024-11-16
DOI: 10.3390/fluids9110266
Issue No: Vol. 9, No. 11 (2024)
- Fluids, Vol. 9, Pages 267: Acceleration of Modeling Capability for GDI
Spray by Machine-Learning Algorithms
Authors: Yassine El Marnissi, Kyungwon Lee, Joonsik Hwang
First page: 267
Abstract: Cold start causes a high amount of unburned hydrocarbon and particulate matter emissions in gasoline direct injection (GDI) engines. Therefore, it is necessary to understand the dynamics of spray during a cold start and develop a predictive model to form a better air-fuel mixture in the combustion chamber. In this study, an Artificial Neural Network (ANN) was designed to predict quantitative 3D liquid volume fraction, liquid penetration, and liquid width under different operating conditions. The model was trained with data derived from high-speed and Schlieren imaging experiments with a gasoline surrogate fuel, conducted in a constant volume spray vessel. A coolant circulator was used to simulate the low-temperature conditions (−7 °C) typical of cold starts. The results showed good agreement between machine learning predictions and experimental data, with an overall accuracy R2 of 0.99 for predicting liquid penetration and liquid width. In addition, the developed ANN model was able to predict detailed dynamics of spray plumes. This confirms the robustness of the ANN in predicting spray characteristics and offers a promising tool to enhance GDI engine technologies.
Citation: Fluids
PubDate: 2024-11-18
DOI: 10.3390/fluids9110267
Issue No: Vol. 9, No. 11 (2024)
- Fluids, Vol. 9, Pages 268: Mesh Sensitivity Analysis of Axisymmetric
Models for Smooth–Turbulent Transient Flows
Authors: Pedro Leite Ferreira, Dídia Isabel Cameira Covas
First page: 268
Abstract: The current paper focuses on the assessment of radial mesh influence on the description of the transient event obtained by an axisymmetric model. The objective is to reduce computational effort while accurately calculating hydraulic transients in smooth–turbulent pressurized pipes. The analyzed pipe system has a reservoir–pipe–valve configuration with an inner diameter of 0.02 m and a total length of 14.96 m, with the initial discharge being equal to 120 × 10−3 L/s (Re = 7638). An extensive study is carried out with 80 geometric sequence meshes by varying the total number of cylinders, the geometric common ratio, and the pipe axial discretization. The benefit of increasing the geometric common ratio is highlighted. A detailed comparison between two meshes is presented, in which the best mesh (i.e., the one with the lowest computational effort) has a three-fold higher value of the geometric common ratio. The two meshes show small differences for the instantaneous valve closure, limited to a time interval immediately after the arrival of the pressure surge and only during the first pressure wave. The dynamic characterization of the transient phenomenon demonstrates the in-depth consistency between the model results and the hydraulic transients’ phenomenon in terms of the piezometric head, the wall shear stress, and the mean velocity time-history, in comparison to the results obtained with the shear stress, lateral velocity, and axial velocity profiles.
Citation: Fluids
PubDate: 2024-11-19
DOI: 10.3390/fluids9110268
Issue No: Vol. 9, No. 11 (2024)
- Fluids, Vol. 9, Pages 269: The Influence of Different ECMO Cannulation
Site and Blood Perfusion Conditions on the Aortic Hemodynamics: A
Computational Fluid Dynamic Model
Authors: Vera Gramigna, Arrigo Palumbo, Gionata Fragomeni
First page: 269
Abstract: Extracorporeal Membrane Oxygenation (ECMO) is a medical device used to support patients with severe cardiac and/or respiratory failure. It is being used more frequently to offer percutaneous mechanical circulatory support, even though the intricate interactions between ECMO and the failing heart, as well as its impact on hemodynamics and perfusion, are not yet fully understood. Within the two main types of ECMO support (the veno-venous ECMO (VV-ECMO), which is used to support only the lungs) and the veno-arterial ECMO (VA-ECMO), which is used to support the lungs and heart), consideration is given solely to the second approach. Indeed, this study focuses on the impact of different ECMO cannulation site and blood perfusion conditions on the aortic hemodynamics and organ perfusion in VA-ECMO. Using computed tomography (CT) images, we reconstructed specific aortic models based on clinical cannula configurations and placements. A detailed cannula-aorta integration model was developed to simulate the VA-ECMO blood supply environment. Employing computational fluid dynamics (CFD), we analyzed how varying ECMO perfusion levels and ECMO cannulation sites affect flow characteristics. This study provides insights into optimizing ECMO therapy by understanding its effects on blood flow and potential damage to blood and organs.
Citation: Fluids
PubDate: 2024-11-19
DOI: 10.3390/fluids9110269
Issue No: Vol. 9, No. 11 (2024)
- Fluids, Vol. 9, Pages 242: Magneto-eklinostrophic Flow, Electromagnetic
Columns, and von Kármán Vortices in Magneto-Fluid Dynamics
Authors: Peter Vadasz
First page: 242
Abstract: An analogy between magneto-fluid dynamics (MFD/MHD) and geostrophic flow in a rotating frame of reference, including the existence of electromagnetic columns identical to Taylor–Proudman columns, is identified and demonstrated theoretically here. The latter occurs within the limit of large values of a dimensionless group representing the magnetic field number. Such conditions are shown to be easily satisfied in reality. Consequently, the electromagnetic fluid flow subject to these conditions is two dimensional and the streamlines are shown to be identical to the pressure lines, in complete analogy to rotating geostrophic flows. These results suggest that von Kármán vortices are anticipated in the wake of virtual electromagnetic columns. An experimental setup is suggested to confirm the theoretical results experimentally.
Citation: Fluids
PubDate: 2024-10-18
DOI: 10.3390/fluids9100242
Issue No: Vol. 9, No. 10 (2024)
- Fluids, Vol. 9, Pages 243: Numerical Simulations of Impact River
Morphology Evolution Mechanism Under the Influence of Floodplain
Vegetation
Authors: Heng Xiang, Zhimeng Zhang, Chunning Ji, Dong Xu, Xincong Chen, Lian Tang, Yuelei Wang
First page: 243
Abstract: Shallow floodplains play a crucial role in river basins by providing essential ecological, hydrological, and geomorphic functions. During floods, intricate hydrodynamic conditions arise as flow exits and re-enters the river channel, interacting with the shallow vegetation. The influence and mechanism of shoal vegetation on channel hydrodynamics, bed topography, and sediment transport remain poorly understood. This study employs numerical simulations to address this gap, focusing on the Xiaolangdi–Taochengpu river section downstream of the Yellow River. Sinusoidal-derived curves are applied to represent the meandering river channel to simulate the river’s evolutionary process at a true scale. The study simulated the conditions of bare and vegetated shallow areas using rigid water-supported vegetation with the same diameter but varying spacing. The riverbed substrate was composed of non-cohesive sand and gravel. The analysis examined alterations in in-channel sediments, bed morphology, and bed heterogeneity in relation to variations in vegetation density. Findings indicated a positive correlation between vegetation density and bed heterogeneity, implying that the ecological complexity of river habitats can be enhanced under natural hydrological conditions in shallow plain vegetation and riparian diffuse flow. Therefore, for biological river restoration, vegetation planting in shallow plain regions can provide greater effectiveness.
Citation: Fluids
PubDate: 2024-10-20
DOI: 10.3390/fluids9100243
Issue No: Vol. 9, No. 10 (2024)
- Fluids, Vol. 9, Pages 244: Optimization of Rotational Hydrodynamic
Cavitation Reactor Geometry
Authors: Maxim Omelyanyuk, Alexey Ukolov, Irina Pakhlyan, Nikolay Bukharin, Mouhammad El Hassan
First page: 244
Abstract: A Rotary-Pulsation Apparatus (RPA), also known in the literature as a Rotational Hydrodynamic Cavitation Reactor (RHCR), is a device which typically consists of a rotating mechanism that generates pulsations or vibrations within a fluid. This can be achieved through various means such as mechanical agitation, pneumatic pulses, or hydraulic forces. It is widely used in food, chemical, pharmaceutical, and microbiological industries to improve the mixing of different fluids, dispersion, pasteurization, and sterilization. In the present paper, a CFD study was conducted to develop and optimize the geometry of the RPA’s rotor and stator to induce cavitation in the fluid flow. The effect of cavitation has the potential to improve dispersion and emulsion properties and to significantly reduce operation pressure, in comparison to conventional mixing systems.
Citation: Fluids
PubDate: 2024-10-20
DOI: 10.3390/fluids9100244
Issue No: Vol. 9, No. 10 (2024)
- Fluids, Vol. 10, Pages 1: Impact of Addition of a Newtonian Solvent to a
Giesekus Fluid: Analytical Determination of Flow Rate in Plane Laminar
Motion
Authors: Irene Daprà, Giambattista Scarpi, Vittorio Di Federico
First page: 1
Abstract: In this study, the influence of the presence of a Newtonian solvent on the flow of a Giesekus fluid in a plane channel or fracture is investigated with a focus on the determination of the flow rate for an assigned external pressure gradient. The pressure field is nonlinear due to the presence of the normal transverse stress component. As expected, the flow rate per unit width Q′ is larger than for a Newtonian fluid and decreases as the solvent increases. It is strongly dependent on the viscosity ratio ε (0≤ε≤1), the dimensionless mobility parameter β (0≤β≤1) and the Deborah number De, the dimensionless driving pressure gradient. The degree of dependency is notably strong in the low range of ε. Furthermore, Q′ increases with De and tends to a constant asymptotic value for large De, subject to the limitation of laminar flow. When the mobility factor β is in the range 0.5÷1, there is a minimum value of ε to obtain an assigned value of De. The ratio UN/U between Newtonian and actual mean velocity depends only on the product βDe, as for other non-Newtonian fluids.
Citation: Fluids
PubDate: 2024-12-24
DOI: 10.3390/fluids10010001
Issue No: Vol. 10, No. 1 (2024)
- Fluids, Vol. 10, Pages 2: Rarefied Nozzle Flow Computation Using the
Viscosity-Based Direct Simulation Monte Carlo Method
Authors: Deepa Raj Mopuru, Nishanth Dongari, Srihari Payyavula
First page: 2
Abstract: Micro-nozzles are essential for enabling precise satellite attitude control and orbital maneuvers. Accurate prediction of performance parameters, including thrust and specific impulse, is critical, necessitating careful design of these nozzles. Given the high Knudsen numbers associated with micro-nozzle flows, rarefied gas dynamics often dominate, and conventional computational fluid dynamics (CFD) methods fail to capture accurate flow expansion behavior. The Direct Simulation Monte Carlo (DSMC) method, developed by Bird, is widely used for modeling rarefied flows; however, it has been primarily implemented on platforms like OpenFOAM and FORTRAN, with limited exploration in MATLAB. This study presents the development of a viscosity-based DSMC (μDSMC) simulation framework in MATLAB for analyzing rarefied gas expansion through micro-nozzles. Key boundary conditions, including upstream and downstream pressure conditions and thermal wall treatments with diffuse reflection, are incorporated into the code. The μDSMC results are validated against traditional DSMC outcomes, showing strong agreement. Grid convergence studies indicate that the radial grid size must be less than one-third of the mean free path, with a more relaxed requirement on axial grid size. Flow characteristics within micro-nozzles are evaluated across varying ambient pressures and gas species in terms of the back pressure ratio, effective exit flow ratio, and exit flow velocity. Studies indicated that a minimum back pressure ratio is required, beyond which the effective nozzle flow expansion is achieved. Parametric analysis further suggests that gases with lower molecular weights are preferable for achieving optimal expansion in micro-nozzles under low ambient pressures.
Citation: Fluids
PubDate: 2024-12-24
DOI: 10.3390/fluids10010002
Issue No: Vol. 10, No. 1 (2024)
- Fluids, Vol. 10, Pages 3: Damage on a Solid–Liquid Interface Induced
by the Dynamical Behavior of Injected Gas Bubbles in Flowing Mercury
Authors: Hiroyuki Kogawa, Takashi Wakui, Masatoshi Futakawa
First page: 3
Abstract: Microbubbles have been applied in various fields. In the mercury targets of spallation neutron sources, where cavitation damage is a crucial issue for life estimation, microbubbles are injected into the mercury to absorb the thermal expansion of the mercury caused by the pulsed proton beam injection and reduce the macroscopic pressure waves, which results in reducing the damage. Recently, when the proton beam power was increased and the number of injected gas bubbles was increased, unique damage morphologies were observed on the solid–liquid interface. Detailed observation and numerical analyses revealed that the microscopic pressure emitted from the gas bubbles contracting is sufficient to form pit damage, i.e., the directions of streak-like defects which are formed by connecting the pit damage coincides with the direction of the gas bubble trajectories, and the distances between the pits was understandable when taking the natural period of gas bubble vibration into account. This indicates that gas microbubbles, used to reduce macroscopic pressure waves, have the potential to be inceptions of cavitation damage due to the microscopic pressure emitted from these gas bubbles. To completely mitigate the damage, we have to consider the two effects of injecting gas bubbles: reducing macroscopic pressure waves and reducing the microscopic pressure due to bubble dynamics.
Citation: Fluids
PubDate: 2024-12-26
DOI: 10.3390/fluids10010003
Issue No: Vol. 10, No. 1 (2024)
- Fluids, Vol. 10, Pages 4: Large-Eddy Simulation of the Flow Past a
Circular Cylinder at Re = 130,000: Effects of Numerical Platforms and
Single- and Double-Precision Arithmetic
Authors: Dmitry A. Lysenko
First page: 4
Abstract: Numerical simulations of sub-critical flow past a circular cylinder at Reynolds number Re = 130,000 are performed using two numerical platforms: the commercial, Ansys Fluent, and the open-source, OpenFOAM (finite volume method and large-eddy simulation based on a differential equation for the sub-grid kinetic energy). An overview of the available experimental data and similar large-eddy simulation studies is presented. A detailed analysis of all accumulated data demonstrates satisfactory agreement between them with a dispersion of approximately 20% for the main integral flow parameters. A detailed comparison of the results obtained using single- and double-precision numerical methods in Ansys Fluent did not reveal any noticeable discrepancies in the integral and local flow parameters as well as the spectral characteristics. It is shown that the behavior of the dynamic system of the fluid dynamic equations computed with single precision is stable by Lyapunov and does not lead to any loss of accuracy. The reconstructed attractors of the dynamic systems in phase space are limited by an ellipsoid.
Citation: Fluids
PubDate: 2024-12-26
DOI: 10.3390/fluids10010004
Issue No: Vol. 10, No. 1 (2024)
- Fluids, Vol. 10, Pages 5: Intra-Cardiac Kinetic Energy and Ventricular
Flow Analysis in Bicuspid Aortic Valve: Impact on Left Ventricular
Function, Dilation Severity, and Surgical Referral
Authors: Ali Fatehi Hassanabad, Julio Garcia
First page: 5
Abstract: Intra-cardiac kinetic energy (KE) and ventricular flow analysis (VFA), as derived from 4D-flow MRI, can be used to understand the physiological burden placed on the left ventricle (LV) due to bicuspid aortic valve (BAV). Our hypothesis was that the KE of each VFA component would impact the surgical referral outcome depending on LV function decrement, BAV phenotype, and aortic dilation severity. A total of 11 healthy controls and 49 BAV patients were recruited. All subjects underwent cardiac magnetic resonance imaging (MRI) examination. The LV mass was inferior in the controls than in the BAV patients (90 ± 26 g vs. 45 ± 17 g, p = 0.025), as well as the inferior ascending aorta diameter indexed (15.8 ± 2.5 mm/m2 vs. 19.3 ± 3.5 mm/m2, p = 0.005). The VFA KE was higher in the BAV group; significant increments were found for the maximum KE and mean KE in the VFA components (p < 0.05). A total of 14 BAV subjects underwent surgery after the scans. When comparing BAV nonsurgery vs. surgery-referred cohorts, the maximum KE and mean KE were elevated (p < 0.05). The maximum and mean KE were also associated with surgical referral (r = 0.438, p = 0.002 and r = 0.371, p = 0.009, respectively). In conclusion, the KE from VFA components significantly increased in BAV patients, including in BAV patients undergoing surgery.
Citation: Fluids
PubDate: 2024-12-27
DOI: 10.3390/fluids10010005
Issue No: Vol. 10, No. 1 (2024)
- Fluids, Vol. 10, Pages 6: Investigation of the Pulmonary Artery
Hypertension Using an Ad Hoc OpenFOAM CFD Solver
Authors: Francesco Duronio, Paola Marchetti
First page: 6
Abstract: Cardiovascular diseases are a group of disorders that affect the heart and blood vessels, representing a leading cause of death worldwide. With the help of computational fluid dynamics, it is possible to study the hemodynamics of the pulmonary arteries in detail and simulate various physiological conditions, thus offering numerous advantages over invasive analyses in the phases of diagnosis and surgical planning. Specifically, the aim of this study is the fluid dynamic analysis of the pulmonary artery, comparing the characteristics of the blood flow in a healthy subject with that of a patient affected by pulmonary arterial hypertension. We performed CFD simulations with the OpenFOAM C++ library using a purposely developed solver that features the Windkessel model as a pressure boundary condition. This methodology, scarcely applied in the past for this problem, allows for a proficient analysis and the detailed quantification of the most important fluid-dynamic parameters (flow velocity, pressure distribution, and wall shear stress (WSS)) with improved accuracy and resolution when compared with classical simulation and diagnostic techniques. We verified the validity of the adopted methodology in reproducing the blood flow by relying on experimental data. A detailed comparative analysis highlights the differences between healthy and pathological cases in hemodynamic terms. The outcomes of this work contribute to enlarging the knowledge of the blood flow characteristics in the human pulmonary artery, revealing substantial differences between the two clinical scenarios investigated and highlighting how arterial hypertension drastically changes the blood flow. The analysis of the data confirmed the importance of CFD as a supportive tool in understanding, diagnosing, and monitoring the pathophysiological mechanisms underlying cardiovascular diseases, proving to be a powerful means for personalizing surgical treatments.
Citation: Fluids
PubDate: 2024-12-29
DOI: 10.3390/fluids10010006
Issue No: Vol. 10, No. 1 (2024)
- Fluids, Vol. 10, Pages 7: Numerical Simulation of First-Order Surface
Reaction in Open Cavity Using Lattice Boltzmann Method
Authors: Cristian Yoel Quintero-Castañeda, María Margarita Sierra-Carrillo, Arturo I. Villegas-Andrade, Javier Burgos-Vergara
First page: 7
Abstract: The lattice Boltzmann method (LBM) is a finite element and finite volume method for studying the reaction rate, mass diffusion and concentration of species. We are used the LBM to investigate the effect of the Damköhler number (Da) and Reynolds number (Re) on the laminar flow in a channel with an open square cavity and a reactive bottom wall in two dimensions in a first-order chemical reaction. The reactant A is transported through the cavity, where it undergoes a reaction on the reactive surface, resulting in the synthesis of product B. The effect of Da < 1 on the reaction rate is negligible for all investigated Re values; the generation of product B is slower because of the effect of the momentum diffusivity on the velocity inside the cavity. For Re = 5 and 1 < Da ≤ 100, the concentration of B inside the cavity reaches the maximum for Da = 100, and A is absorbed almost entirely on the bottom of the cavity. In our simulations, we observed that for all values of Re and Da > 100, the effect of the momentum diffusivity is negligible in the cavity, and the reaction on the surface is almost instantaneous.
Citation: Fluids
PubDate: 2024-12-30
DOI: 10.3390/fluids10010007
Issue No: Vol. 10, No. 1 (2024)
