Fluids

22 pages, 4485 KiB

Open AccessArticle

Experimental Solid–Liquid Mass Transfer around Free-Moving Particles in an Air-Lift Membrane Bioreactor with Optical Techniques

by Naila Bouayed, Manon Montaner, Claude Le Men, Johanne Teychené, Christine Lafforgue, Nicolas Dietrich, Chung-Hak Lee and Christelle Guigui

Fluids 2022, 7(10), 338; https://doi.org/10.3390/fluids7100338 - 21 Oct 2022

Cited by 2 | Viewed by 1665

Abstract

This article focuses on the study of the mass transfer involved in the application of a bacterial antifouling technique for membrane bioreactors (MBR), via the addition of solid media. These alginate objects can contain a biological system capable of producing an enzyme that [...] Read more.

This article focuses on the study of the mass transfer involved in the application of a bacterial antifouling technique for membrane bioreactors (MBR), via the addition of solid media. These alginate objects can contain a biological system capable of producing an enzyme that degrades the signal molecules responsible for membrane fouling. The objective of this article is to quantify the mass transfer by distinguishing two main types: the transfer from the liquid to the solid media and the transfer from solid media to the liquid phase. For this purpose, a model molecule was chosen, and experiments were specifically developed with an optical device to track the concentration of the dye in the liquid phase, considering three different shapes for the particles (beads, hollow cylinders, and flat sheets). The experiments were first performed in jar tests and then in a lab-scale reactor. The results of this study revealed that the total amount of dye transferred into the sheets was greater than that transferred into the cylinders or the beads, which was attributed to the sheets having a larger exchange area for the same volume. When the dyed media were implemented in the MBR (loading rate of solid media: 0.45% v/v—no biomass), the global transfer coefficient from the sheets to the liquid was found to be greater than for the other shapes, indicating a faster transfer phenomenon. The effect of aeration in the MBR was investigated and an optimal air flowrate for fostering the transfer was found, based on the highest transfer coefficient that was obtained. This study provided key information about mass transfer in MBRs and how it is affected by the particle shapes and the MBR operating conditions. Full article

(This article belongs to the Collection Advances in Flow of Multiphase Fluids and Granular Materials)

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26 pages, 5886 KiB

Open AccessEditor’s ChoiceArticle

Evaluation of RANS-DEM and LES-DEM Methods in OpenFOAM for Simulation of Particle-Laden Turbulent Flows

by Atul Jaiswal, Minh Duc Bui and Peter Rutschmann

Fluids 2022, 7(10), 337; https://doi.org/10.3390/fluids7100337 - 21 Oct 2022

Cited by 10 | Viewed by 4096

Abstract

CFD-DEM modelling of particle-laden turbulent flow is challenging in terms of the required and obtained CFD resolution, heavy DEM computations, and the limitations of the method. Here, we assess the efficiency of a particle-tracking solver in OpenFOAM with RANS-DEM and LES-DEM approaches under [...] Read more.

CFD-DEM modelling of particle-laden turbulent flow is challenging in terms of the required and obtained CFD resolution, heavy DEM computations, and the limitations of the method. Here, we assess the efficiency of a particle-tracking solver in OpenFOAM with RANS-DEM and LES-DEM approaches under the unresolved CFD-DEM framework. Furthermore, we investigate aspects of the unresolved CFD-DEM method with regard to the coupling regime, particle boundary condition and turbulence modelling. Applying one-way and two-way coupling to our RANS-DEM simulations demonstrates that it is sufficient to include one-way coupling when the particle concentration is small (O ~

10^{- 5}

). Moreover, our study suggests an approach to estimate the particle boundary condition for cases when data is unavailable. In contrast to what has been previously reported for the adopted case, our RANS-DEM results demonstrate that simple dispersion models considerably underpredict particle dispersion and previously observed reasonable particle dispersion were due to an error in the numerical setup rather than the used dispersion model claiming to include turbulence effects on particle trajectories. LES-DEM may restrict extreme mesh refinement, and, under such scenarios, dynamic LES turbulence models seem to overcome the poor performance of static LES turbulence models. Sub-grade scale effects cannot be neglected when using coarse mesh resolution in LES-DEM and must be recovered with efficient modelling approaches to predict accurate particle dispersion. Full article

(This article belongs to the Section Flow of Multi-Phase Fluids and Granular Materials)

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20 pages, 7300 KiB

Open AccessArticle

Effect of Axial and Radial Flow on the Hydrodynamics in a Taylor Reactor

by Sebastian A. Altmeyer

Fluids 2022, 7(10), 336; https://doi.org/10.3390/fluids7100336 - 20 Oct 2022

Cited by 2 | Viewed by 2623

Abstract

This paper investigates the impact of combined axial through flow and radial mass flux on Taylor–Couette flow in a counter-rotating configuration, in which different branches of nontrivial solutions appear via Hopf bifurcations. Using direct numerical simulation, we elucidate flow structures, dynamics, and bifurcation [...] Read more.

This paper investigates the impact of combined axial through flow and radial mass flux on Taylor–Couette flow in a counter-rotating configuration, in which different branches of nontrivial solutions appear via Hopf bifurcations. Using direct numerical simulation, we elucidate flow structures, dynamics, and bifurcation behavior in qualitative and quantitative detail as a function of axial Reynolds numbers (

R e

) and radial mass flux (

α

) spanning a parameter space with a very rich variety of solutions. We have determined nonlinear properties such as anharmonicity, asymmetry, flow rates (axial and radial) and torque for toroidally closed Taylor vortices and helical spiral vortices. Small to moderate radial flow

α

initially decreases the symmetry of the different flows, before for larger values,

α

, the symmetry eventually increases, which appears to be congruent with the degree of anharmonicity. Enhancement in the total torque with

α

are elucidated whereby the strength varies for different flow structures, which allows for potential better selection and control. Further, depending on control parameters, heteroclinic connections (and cycles) of oscillatory type in between unstable and topological different flow structures are detected. The research results provide a theoretical basis for simple modification the conventional Taylor flow reactor with a combination of additional mass flux to enhance the mass transfer mechanism. Full article

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22 pages, 2426 KiB

Open AccessReview

Dilational Rheology of Fluid/Fluid Interfaces: Foundations and Tools

by Eduardo Guzmán, Armando Maestro, Carlo Carbone, Francisco Ortega and Ramón G. Rubio

Fluids 2022, 7(10), 335; https://doi.org/10.3390/fluids7100335 - 20 Oct 2022

Cited by 10 | Viewed by 2793

Abstract

Fluid/fluid interfaces are ubiquitous in science and technology, and hence, the understanding of their properties presents a paramount importance for developing a broad range of soft interface dominated materials, but also for the elucidation of different problems with biological and medical relevance. However, [...] Read more.

Fluid/fluid interfaces are ubiquitous in science and technology, and hence, the understanding of their properties presents a paramount importance for developing a broad range of soft interface dominated materials, but also for the elucidation of different problems with biological and medical relevance. However, the highly dynamic character of fluid/fluid interfaces makes shedding light on fundamental features guiding the performance of the interfaces very complicated. Therefore, the study of fluid/fluid interfaces cannot be limited to an equilibrium perspective, as there exists an undeniable necessity to face the study of the deformation and flow of these systems under the application of mechanical stresses, i.e., their interfacial rheology. This is a multidisciplinary challenge that has been evolving fast in recent years, and there is currently available a broad range of experimental and theoretical methodologies providing accurate information of the response of fluid/fluid interfaces under the application of mechanical stresses, mainly dilational and shear. This review focused on providing an updated perspective on the study of the response of fluid/fluid interfaces to dilational stresses; to open up new avenues that enable the exploitation of interfacial dilational rheology and to shed light on different problems in the interest of science and technology. Full article

(This article belongs to the Special Issue Recent Advances in Fluid Mechanics: Feature Papers, 2022)

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24 pages, 15115 KiB

Open AccessArticle

A Bayesian Nonlinear Reduced Order Modeling Using Variational AutoEncoders

by Nissrine Akkari, Fabien Casenave, Elie Hachem and David Ryckelynck

Fluids 2022, 7(10), 334; https://doi.org/10.3390/fluids7100334 - 20 Oct 2022

Cited by 6 | Viewed by 2750

Abstract

This paper presents a new nonlinear projection based model reduction using convolutional Variational AutoEncoders (VAEs). This framework is applied on transient incompressible flows. The accuracy is obtained thanks to the expression of the velocity and pressure fields in a nonlinear manifold maximising the [...] Read more.

This paper presents a new nonlinear projection based model reduction using convolutional Variational AutoEncoders (VAEs). This framework is applied on transient incompressible flows. The accuracy is obtained thanks to the expression of the velocity and pressure fields in a nonlinear manifold maximising the likelihood on pre-computed data in the offline stage. A confidence interval is obtained for each time instant thanks to the definition of the reduced dynamic coefficients as independent random variables for which the posterior probability given the offline data is known. The parameters of the nonlinear manifold are optimized as the ones of the decoder layers of an autoencoder. The parameters of the conditional posterior probability of the reduced coefficients are the ones of the encoder layers of the same autoencoder. The optimization of both sets of the encoder and the decoder parameters is obtained thanks to the application of a variational Bayesian method, leading to variational autoencoders. This Reduced Order Model (ROM) is not a regression model over the offline pre-computed data. The numerical resolution of the ROM is based on the Chorin projection method. We apply this new nonlinear projection-based Reduced Order Modeling (ROM) for a 2D Karman Vortex street flow and a 3D incompressible and unsteady flow in an aeronautical injection system. Full article

(This article belongs to the Special Issue Next-Generation Methods for Turbulent Flows)

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20 pages, 8195 KiB

Open AccessArticle

Effect of the Pore Geometry on the Driving Pressure across a Bubble Penetrating a Single Pore

by Shadi Ansari and David S. Nobes

Fluids 2022, 7(10), 333; https://doi.org/10.3390/fluids7100333 - 20 Oct 2022

Cited by 5 | Viewed by 2322

Abstract

The passage of a bubble and the required energy for its motion through a confining pore can potentially be affected by the surface roughness and geometry of the pore. The motion of an isolated bubble passing through four different pore geometries (three circular [...] Read more.

The passage of a bubble and the required energy for its motion through a confining pore can potentially be affected by the surface roughness and geometry of the pore. The motion of an isolated bubble passing through four different pore geometries (three circular pores, a smooth pore and 2 with different roughness, and a sharp triangular pore) is investigated. The shape of the deformed bubble passing these geometries was evaluated to determine the pressure drop across the bubble and hence the driving force to cause motion. The results of investigating the motion of the bubbles and the change in the pressure and velocity of the bubbles showed that the pore shape and surface roughness have a significant effect on the passage of the isolated phase. The motion of the bubble entering the entrance of the circular pores was similar for all circular cases. On exiting, however, a clear difference between the cases due to the presence of the peaks of the roughness was observed. These results indicate that, in addition to the critical pressure at the entrance of the pore, extra resistance will be introduced due to bubble phase pinning at the exit caused by roughness of the pore. Full article

(This article belongs to the Special Issue Recent Advances in Fluid Mechanics: Feature Papers, 2022)

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20 pages, 6983 KiB

Open AccessArticle

Body Morphology and Drag in Swimming: CFD Analysis of the Effects of Differences in Male and Female Body Types

by Andrew X. G. Wang and Zbigniew J. Kabala

Fluids 2022, 7(10), 332; https://doi.org/10.3390/fluids7100332 - 19 Oct 2022

Cited by 7 | Viewed by 3929

Abstract

This study analyzes the effect of the morphological characteristics of swimmers on passive drag and determines whether the female or male body type is more efficient for gliding. As a result of puberty, males and females develop different body structures; this study investigates [...] Read more.

This study analyzes the effect of the morphological characteristics of swimmers on passive drag and determines whether the female or male body type is more efficient for gliding. As a result of puberty, males and females develop different body structures; this study investigates whether these changes in shape influence drag. Computational fluid dynamics (CFD) simulations carried out in Ansys Fluent software were used to calculate the drag force and coefficient from 2D models of swimmers in streamline position, generated based on common anthropometric measurements. Both the top and side view profiles of the swimmers were simulated, unique to this study. The normalized male and female body shapes were simulated at different velocities, and it was demonstrated that the male body shape has a lower drag coefficient than the female body shape by 10.1% and 2.8% for top view and side view profiles, respectively. The in-depth analysis and simulation of models with varying hip and chest dimensions found a significant and positive correlation between hip and chest size and drag, with the chest size having the largest effect of an average 12.2% increase in drag per 5% increase in chest breadth. The results from modifying anthropometric variables explain the discrepancy between the drag experienced by male and female swimmers and show that enlarged hips and chests cause an increase in resistance. The differences between drag for males and females were found to be comparable to the 6.2% and 7.7% drag differences between full-body fastskin and normal suits, indicating measurable impact on performance. These findings suggest that the morphology of swimmers does have a significant effect on drag and that the male body shape is more hydrodynamic than the female body shape. Full article

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22 pages, 8514 KiB

Open AccessArticle

CFD Investigation into the Effects of Surrounding Particle Location on the Drag Coefficient

by David Dodds, Abd Alhamid R. Sarhan and Jamal Naser

Fluids 2022, 7(10), 331; https://doi.org/10.3390/fluids7100331 - 17 Oct 2022

Cited by 4 | Viewed by 2191

Abstract

In the simulation of dilute gas-solid flows such as those seen in many industrial applications, the Lagrangian Particle Tracking method is used to track packets of individual particles through a converged fluid field. In the tracking of these particles, the most dominant forces [...] Read more.

In the simulation of dilute gas-solid flows such as those seen in many industrial applications, the Lagrangian Particle Tracking method is used to track packets of individual particles through a converged fluid field. In the tracking of these particles, the most dominant forces acting upon the particles are those of gravity and drag. In order to accurately predict particle motion, the determination of the aforementioned forces become of the upmost importance, and hence an improved drag force formula was developed to incorporate the effects of particle concentration and particle Reynolds number. The present CFD study examines the individual effects of particles located both perpendicular and parallel to the flow direction, as well as the effect of a particle entrain within an infinite matrix of evenly distributed particles. Results show that neighbouring particles perpendicular to the flow (Model 2) have an effect of increasing the drag force at close separation distances, but this becomes negligible between 5–10 particle diameters depending on particle Reynolds number (Re_p). When entrained in an infinite line of particles co-aligned with the flow (Model 1), the drag force is remarkably reduced at close separation distances and increases as the distance increases. The results of the infinite matrix of particles (Model 3) show that, although not apparent in the individual model, the effect of side particles is experienced many particle diameters downstream. Full article

(This article belongs to the Special Issue Recent Advances in Fluid Mechanics: Feature Papers, 2022)

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11 pages, 899 KiB

Open AccessArticle

Self-Consistent Hydrodynamic Model of Electron Vortex Fluid in Solids

by Victor L. Mironov

Fluids 2022, 7(10), 330; https://doi.org/10.3390/fluids7100330 - 17 Oct 2022

Cited by 3 | Viewed by 1505

Abstract

We propose a system of self-consistent equations for electron fluid in solids which describes both longitudinal vortex flows and frozen-in internal electromagnetic fields. It is shown that in the case of an ideal electron fluid, the proposed model describes the electrodynamics of the [...] Read more.

We propose a system of self-consistent equations for electron fluid in solids which describes both longitudinal vortex flows and frozen-in internal electromagnetic fields. It is shown that in the case of an ideal electron fluid, the proposed model describes the electrodynamics of the superconductor, and in the vortex-less case, it leads to modified London equations. In addition, the two-fluid model based on the proposed equations is applied to the description of an ideal electron-hole fluid in a semiconductor. The damping processes in a non-ideal electron fluid are described by modified equations, which take into account collisions with a crystal lattice and internal diffuse friction. The main peculiarities of the proposed equations are illustrated with the analysis of electron sound waves. Full article

(This article belongs to the Section Flow of Multi-Phase Fluids and Granular Materials)

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13 pages, 1402 KiB

Open AccessArticle

Freestream Turbulence Effects on the Aerodynamics of an Oscillating Square Cylinder at the Resonant Frequency

by Yongxin Chen, Kamal Djidjeli and Zheng-Tong Xie

Fluids 2022, 7(10), 329; https://doi.org/10.3390/fluids7100329 - 16 Oct 2022

Cited by 1 | Viewed by 2198

Abstract

Flow past a bluff body in freestream turbulence can substantially change the flow behaviour compared to that in smooth inflow. This paper presents the study of wake flow and aerodynamics of an oscillating square cylinder at the resonant frequency in freestream turbulence, with [...] Read more.

Flow past a bluff body in freestream turbulence can substantially change the flow behaviour compared to that in smooth inflow. This paper presents the study of wake flow and aerodynamics of an oscillating square cylinder at the resonant frequency in freestream turbulence, with the integral length not greater than the cylinder side and the turbulence intensity not greater than 10%. Large eddy simulations (LES) in the Cartesian grid using the Immersed Boundary Method (IBM) technique embedded in a FVM solver, together with an efficient synthetic turbulent inflow generator implemented in an in-house parallel FORTRAN code are used for the study. The results are compared with those for smooth inflow, and relevant data published in the literature. The key findings are: the freestream turbulence conditions evidently reduces the local turbulent scales and fluctuations in the shear layer compared to in smooth flow, as small scale freestream turbulence breaks down cylinder-generated larger scale eddies and weakens them; but does not evidently affect the vortex shedding frequency, or the length of the recirculation region behind the cylinder. This suggests negligible change of drag coefficient compared to in smooth inflow. Moreover, this is because the vortex shedding is dominated by the forced oscillation at the resonance frequency, and the turbulence intensity is small. Full article

(This article belongs to the Special Issue Next-Generation Methods for Turbulent Flows)

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17 pages, 438 KiB

Open AccessArticle

Influence of Gravitational Force on Particle Motion in the Channel Flow Induced by Fluid Injection

by Konstantin Volkov

Fluids 2022, 7(10), 328; https://doi.org/10.3390/fluids7100328 - 14 Oct 2022

Viewed by 1458

Abstract

The motion of an individual particle in a circular channel flow induced with fluid injection is considered. Analysis takes into account drag and gravitational forces acting on an individual particle. The change in the radial structure of the flow in a channel with [...] Read more.

The motion of an individual particle in a circular channel flow induced with fluid injection is considered. Analysis takes into account drag and gravitational forces acting on an individual particle. The change in the radial structure of the flow in a channel with fluid injection on the motion of a particle is studied. A number of simplifying assumptions about the structure of the fluidflow in the channel makes it possible to obtain an analytical solution of the problem for particles. The results of a qualitative analysis of particle trajectories in the channel with fluid injection are compared with numerical simulations. The singular points of the particle trajectory are found in a wide range of characteristic non-dimensional parameters of the problem. The modes of motion of an individual particle in a channel with fluid injection are classified depending on the Stokes and Froude numbers. Full article

(This article belongs to the Special Issue Multiphase Flow in Pipes with and without Porous Media, Volume II)

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31 pages, 1148 KiB

Open AccessArticle

Hamiltonian Variational Formulation of Three-Dimensional, Rotational Free-Surface Flows, with a Moving Seabed, in the Eulerian Description

by Constantinos P. Mavroeidis and Gerassimos A. Athanassoulis

Fluids 2022, 7(10), 327; https://doi.org/10.3390/fluids7100327 - 14 Oct 2022

Cited by 2 | Viewed by 1993

Abstract

Hamiltonian variational principles have provided, since the 1960s, the means of developing very successful wave theories for nonlinear free-surface flows, under the assumption of irrotationality. This success, in conjunction with the recognition that almost all flows in the sea are not irrotational, raises [...] Read more.

Hamiltonian variational principles have provided, since the 1960s, the means of developing very successful wave theories for nonlinear free-surface flows, under the assumption of irrotationality. This success, in conjunction with the recognition that almost all flows in the sea are not irrotational, raises the question of extending Hamilton’s principle to rotational free-surface flows. The Euler equations governing the bulk fluid motion have been derived by means of Hamilton’s principle since the late 1950s. Nevertheless, a complete variational formulation of the rotational water-wave problem, including the derivation of the free-surface boundary conditions, seems to be lacking until now. The purpose of the present work is to construct such a missing variational formulation. The appropriate functional is the usual Hamilton’s action, constrained by the conservation of mass and the conservation of fluid parcels’ identity. The differential equations governing the bulk fluid motion are derived as usually, applying standard methods of the calculus of variations. However, the standard methodology does not provide enough structure to obtain the free-surface boundary conditions. To overcome this difficulty, differential-variational forms of the aforementioned constraints are introduced and applied to the boundary variations of the Eulerian fields. Under this transformation, both kinematic and dynamic free-surface conditions are naturally derived, ensuring the Hamiltonian variational formulation of the complete problem. An interesting feature, appearing in the present variational derivation, is a dual possibility concerning the tangential velocity on the boundary; it may be either the same as in irrotational flow (no condition) or zero, corresponding to the small-viscosity limit. The deeper meaning and the significance of these findings seem to deserve further analysis. Full article

(This article belongs to the Special Issue Nonlinear Wave Hydrodynamics, Volume II)

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18 pages, 6871 KiB

Open AccessArticle

Principles of Unsteady High-Speed Flow Control Using a Time-Limited Thermally Stratified Energy Source

by Olga A. Azarova and Oleg V. Kravchenko

Fluids 2022, 7(10), 326; https://doi.org/10.3390/fluids7100326 - 12 Oct 2022

Cited by 3 | Viewed by 1512

Abstract

This study focused on the development of the unsteady impact of a thermally stratified energy source on a supersonic flow around an aerodynamic (AD) body in a viscous heat-conducting gas (air). Research was based on the Navier-Stokes equations. The freestream Mach number was [...] Read more.

This study focused on the development of the unsteady impact of a thermally stratified energy source on a supersonic flow around an aerodynamic (AD) body in a viscous heat-conducting gas (air). Research was based on the Navier-Stokes equations. The freestream Mach number was 2. A new multi-vortex mechanism of the impact of a time-limited stratified energy source on the aerodynamic characteristics of a body was described. Almost complete destruction of the bow shock wave in the density field, due to the multiple generation of Richtmyer-Meshkov instabilities in the region of a stratified energy source, was obtained. The dependences of the dynamics of frontal drag and lift forces of a streamlined body on temperature in the source layers were studied. It was determined that, by changing the temperature in the layers of a stratified energy source, it was possible to obtain more intense vortices accompanying the Richtmyer-Meshkov instabilities, causing a temporary decrease in the drag force of an AD body and ensuring the emergence and unsteady change in the magnitude of the lift (pitch) forces. The main principles of unsteady flow control using a stratified energy source were established. Full article

(This article belongs to the Special Issue High Speed Flows)

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23 pages, 2270 KiB

Open AccessReview

Advancements and Opportunities in Characterizing Patient-Specific Wall Shear Stress Imposed by Coronary Artery Stenting

by John F. LaDisa, Jr., Arash Ghorbannia, David S. Marks, Peter Mason and Hiromasa Otake

Fluids 2022, 7(10), 325; https://doi.org/10.3390/fluids7100325 - 11 Oct 2022

Cited by 5 | Viewed by 3694

Abstract

The success of drug-eluting stents (DES) is limited by restenosis and, to a lesser extent, late stent thrombosis. Mechanical stimuli have been implicated in these outcomes, with indices of wall shear stress (WSS) determined from computational simulations being reported most frequently. The current [...] Read more.

The success of drug-eluting stents (DES) is limited by restenosis and, to a lesser extent, late stent thrombosis. Mechanical stimuli have been implicated in these outcomes, with indices of wall shear stress (WSS) determined from computational simulations being reported most frequently. The current work summarizes state-of-the-art computational approaches applicable to patient-specific models aimed at further understanding changes in WSS indexes imposed by stent implantation. We begin with a review of best practices involved in the process and then summarize the literature related to stent-induced WSS alterations. Image-based reconstruction methods are also discussed, along with the latest generation boundary conditions that replicate cardiac physiology and downstream vasculature in the setting of coronary artery disease. The influence of existing material property data on WSS results obtained with geometries reconstructed from finite element modeling and fluid structure interaction (FSI) simulations is reviewed, along with the novel approaches being used to provide coronary artery plaque data that are currently missing from the literature. We also consider the use of machine learning tools that have the potential for impact when assessing the role of adverse stent-induced WSS in suboptimal clinical outcomes. We conclude by focusing on challenging cases that involve DES implantation, which may benefit from recent advancements in patient-specific computational modeling. Full article

(This article belongs to the Special Issue Image-Based Computational and Experimental Biomedical Flows)

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12 pages, 1344 KiB

Open AccessArticle

Winter Ice Dynamics in a Semi-Closed Ice-Covered Sea: Numerical Simulations and Satellite Data

by Ilya Chernov, Alexey Tolstikov, Vyacheslav Baklagin and Nikolay Iakovlev

Fluids 2022, 7(10), 324; https://doi.org/10.3390/fluids7100324 - 11 Oct 2022

Cited by 1 | Viewed by 1768

Abstract

The White Sea is a small shallow sea covered by ice in winter. There are very few numerical models of this sea. For the ice-free sea, much data has been collected, but for winter only a small amount (satellite data only). We use [...] Read more.

The White Sea is a small shallow sea covered by ice in winter. There are very few numerical models of this sea. For the ice-free sea, much data has been collected, but for winter only a small amount (satellite data only). We use our finite-element numerical model Jasmine and satellite data to trace the ice advection and exchange between parts of the White Sea. The aim of the investigation is to adjust the model to adequately reproduce the White Sea ice dynamics. By comparing satellite data on sea-ice concentration with the model prediction, we show that the model describes sea-ice dynamics well, and use it to estimate ice flow from bays to the middle part of the sea and ice exchange through the narrow strait. Ice exchange between neighbouring parts of the sea is shown to be intensive, with large dispersion compared to the time-mean, and bays are shown to be ice producers, while the Gorlo straight is shown to accept ice. We demonstrate that the model is a tool that can be used to better understand the winter regime of the sea. Full article

(This article belongs to the Special Issue Modelling and Observation of Water Waves)

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7 pages, 1346 KiB

Open AccessArticle

Impact of the Soundproofing in the Cavity of the Synthetic Jet Actuator on the Generated Noise

by Emil Smyk and Marek Markowicz

Fluids 2022, 7(10), 323; https://doi.org/10.3390/fluids7100323 - 5 Oct 2022

Cited by 2 | Viewed by 1538

Abstract

The synthetic jet actuator (SJA) generated high noise which limits the area of its application. In this paper, the five actuators with different types of soundproofing in the cavity were tested and compared to the classic actuator. The resistance and the sound pressure [...] Read more.

The synthetic jet actuator (SJA) generated high noise which limits the area of its application. In this paper, the five actuators with different types of soundproofing in the cavity were tested and compared to the classic actuator. The resistance and the sound pressure level (SPL) were measured for real power

P = 1, 2, 4

W, and frequency in a range of 20–150 Hz. The resonant frequency of actuators was designed. Only one type of soundproofing had a significant impact on the resonant frequency. The use of soundproofing in the actuator cavity increased or did not affect the generated noise at a frequency below 120 Hz and only the mineral wool significantly decreased the noise at a frequency above 120 Hz– even 7 dBA. The direction for further investigations was set. Full article

(This article belongs to the Section Turbulence)

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15 pages, 15253 KiB

Open AccessArticle

Vortex Shedding Dynamics Behind a Single Solar PV Panel Over a Range of Tilt Angles in Uniform Flow

by Jose Luis Suárez, David Cadenas, Higinio Rubio and Pablo Ouro

Fluids 2022, 7(10), 322; https://doi.org/10.3390/fluids7100322 - 5 Oct 2022

Cited by 5 | Viewed by 2948

Abstract

Solar photovoltaic (PV) panels are very slender structures that can be equipped with a tracking system to adjust their orientation and maximise their energy yield. Theses slender structures are exposed to wind loads and their aerodynamic response can vary considerably depending on the [...] Read more.

Solar photovoltaic (PV) panels are very slender structures that can be equipped with a tracking system to adjust their orientation and maximise their energy yield. Theses slender structures are exposed to wind loads and their aerodynamic response can vary considerably depending on the wind speed and operating tilt angle (

θ

) that can be in the range of

\pm 60^{\circ}

. Large-eddy simulations are performed to unveil the governing mechanisms involved in the vortex shedding and mean flow separation around a solar PV panel. Our results show that three regimes can be distinguished: at

θ = \pm 10^{\circ}

, leading-edge vortices are shed and convected along the panel’s surface without significant flow separation; at

θ = \pm 10^{\circ} - 35^{\circ}

, a low-frequency large-scale structure governs the vortex shedding with less-energetic tailing- and leading-edge vortices being shed at higher frequencies; and, at

θ = \pm 35^{\circ} - 60^{\circ}

, the flow on the suction side is fully separated by non-symmetric vortex shedding due to the proximity of the structure to the bottom ground. The highest Strouhal number is observed for

θ = \pm 35^{\circ}

at which the tilt moment coefficient is also maximum. Decreasing the distance to the ground slightly increased the Strouhal number for negative tilt angles whilst no changes were observed for positive inclinations. Full article

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15 pages, 2162 KiB

Open AccessArticle

The Electrical Conductivity of Ionic Liquids: Numerical and Analytical Machine Learning Approaches

by Theodoros E. Karakasidis, Filippos Sofos and Christos Tsonos

Fluids 2022, 7(10), 321; https://doi.org/10.3390/fluids7100321 - 5 Oct 2022

Cited by 13 | Viewed by 4749

Abstract

In this paper, we incorporate experimental measurements from high-quality databases to construct a machine learning model that is capable of reproducing and predicting the properties of ionic liquids, such as electrical conductivity. Empirical relations traditionally determine the electrical conductivity with the temperature as [...] Read more.

In this paper, we incorporate experimental measurements from high-quality databases to construct a machine learning model that is capable of reproducing and predicting the properties of ionic liquids, such as electrical conductivity. Empirical relations traditionally determine the electrical conductivity with the temperature as the main component, and investigations only focus on specific ionic liquids every time. In addition to this, our proposed method takes into account environmental conditions, such as temperature and pressure, and supports generalization by further considering the liquid atomic weight in the prediction procedure. The electrical conductivity parameter is extracted through both numerical machine learning methods and symbolic regression, which provides an analytical equation with the aid of genetic programming techniques. The suggested platform is capable of providing either a fast, numerical prediction mechanism or an analytical expression, both purely data-driven, that can be generalized and exploited in similar property prediction projects, overcoming expensive experimental procedures and computationally intensive molecular simulations. Full article

(This article belongs to the Special Issue Machine Learning and Artificial Intelligence in Fluid Mechanics)

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16 pages, 484 KiB

Open AccessArticle

The Single Particle Motion of Non-Spherical Particles in Low Reynolds Number Flow

by Yuri Mendez

Fluids 2022, 7(10), 320; https://doi.org/10.3390/fluids7100320 - 3 Oct 2022

Cited by 1 | Viewed by 2375

Abstract

This research presents a mathematical framework that places the physics and the dynamics of viscosity within a physical environment that captures the effect of the shape and overall weight of non-spherical particles to calculate their settling velocity. It then takes insights derived from [...] Read more.

This research presents a mathematical framework that places the physics and the dynamics of viscosity within a physical environment that captures the effect of the shape and overall weight of non-spherical particles to calculate their settling velocity. It then takes insights derived from the framework to model analytical constructs to solve the motion of a single particle that settles in a fluid that moves horizontally as a whole. These analytical constructs are then shown to be applicable to spherical and non-spherical particles. Full article

(This article belongs to the Collection Advances in Flow of Multiphase Fluids and Granular Materials)

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24 pages, 2808 KiB

Open AccessArticle

Research Progress of Air Lubrication Drag Reduction Technology for Ships

by Hai An, Haozhe Pan and Po Yang

Fluids 2022, 7(10), 319; https://doi.org/10.3390/fluids7100319 - 2 Oct 2022

Cited by 6 | Viewed by 6160

Abstract

Air lubrication is a promising drag reduction technology for ships because it is considered to reduce the skin-friction resistance of ships by changing the energy of turbulent boundary layers. Air lubrication drag reduction can be classified into: microbubble drag reduction (injection of microbubbles [...] Read more.

Air lubrication is a promising drag reduction technology for ships because it is considered to reduce the skin-friction resistance of ships by changing the energy of turbulent boundary layers. Air lubrication drag reduction can be classified into: microbubble drag reduction (injection of microbubbles along the hull), air film drag reduction (using a larger film of air to cover the ship bottom), and air cavity drag reduction (recesses underneath the hull are filled with air). In this paper, the research progress of the air lubrication drag reduction technology is reviewed from experimental and numerical aspects. For these three drag reduction methods, based on the aspect of experimental research, the main research focus is the analysis and evaluation of the influencing factors such as the gas injection form and drag reduction rate; in terms of theoretical research, the accuracy of the simulation calculation depends on the selection of the theoretical calculation model and the analysis of the drag reduction mechanism. The paper introduces, in detail, the typical experimental phenomena and the theoretical results of a numerical study of three types of drag reduction methods, revealing the essence of air lubrication technology to achieve drag reduction by changing the physical properties of the turbulent boundary layer. Full article

(This article belongs to the Special Issue Aerodynamics and Aeroacoustics of Vehicles, Volume II)

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19 pages, 3971 KiB

Open AccessReview

Physics of Dynamic Contact Line: Hydrodynamics Theory versus Molecular Kinetic Theory

by Alireza Mohammad Karim and Wieslaw J. Suszynski

Fluids 2022, 7(10), 318; https://doi.org/10.3390/fluids7100318 - 30 Sep 2022

Cited by 7 | Viewed by 3623

Abstract

The dynamic contact line plays a key role in various fields of interfacial physics, including bioprinting, nano-scale printing, three-dimensional printing, biomaterials, tissue engineering, smart materials, flexible printed electronics, biomedicine, and healthcare. However, there is still a lack of thorough physical understanding of its [...] Read more.

The dynamic contact line plays a key role in various fields of interfacial physics, including bioprinting, nano-scale printing, three-dimensional printing, biomaterials, tissue engineering, smart materials, flexible printed electronics, biomedicine, and healthcare. However, there is still a lack of thorough physical understanding of its real behavior in numerous complex problems in nature and technology. The dynamic contact line exhibits a complex conformation in real-life fluid dynamics problems. Therefore, this review presents two main long-standing models that describe the physics of the dynamic contact line: hydrodynamics theory and molecular kinetics theory. Next, the role of the dynamic contact line in current advanced technologies is discussed. Finally, this review discusses future research directions to enhance the power of current physical models of the dynamic contact line. Full article

(This article belongs to the Special Issue Contact Line Dynamics and Droplet Spreading)

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18 pages, 6212 KiB

Open AccessArticle

Numerical Simulation on Temperature and Moisture Fields Around Cooling Towers Used in Mine Ventilation System

by Maxim Zhelnin, Anastasiia Kostina, Oleg Plekhov, Artem Zaitsev and Dmitriy Olkhovskiy

Fluids 2022, 7(10), 317; https://doi.org/10.3390/fluids7100317 - 28 Sep 2022

Cited by 2 | Viewed by 2003

Abstract

For heat rejection, small air-cooling towers are widely used in mine ventilation systems. However, the thermal efficiency of the cooling towers can be significantly affected by their geometrical arrangement and crosswind conditions. In certain ambient conditions, heated air coming from an exit of [...] Read more.

For heat rejection, small air-cooling towers are widely used in mine ventilation systems. However, the thermal efficiency of the cooling towers can be significantly affected by their geometrical arrangement and crosswind conditions. In certain ambient conditions, heated air coming from an exit of one tower can flow to intakes of other towers, which leads to a reduction in the thermal efficiency of the entire ventilation system. The aim of this study was to investigate the influence of crosswind speed and tower spacing on the temperature and moisture content of intakes of cooling towers. For this purpose, a three-dimensional CFD model of the non-isothermal turbulent flow of moist air around cooling towers is proposed. The model is based on the Reynolds-averaged Navier–Stokes equations with a standard turbulence model which are supplemented by heat transfer and moisture transport equations. The investigation of the effects of the crosswind speed and the tower spacing was carried out for two cooling towers by multiparametric numerical simulation using the CFD model. It was shown that the upstream tower protects the downstream one from the effect of the crosswind. The increase in the crosswind speed causes a rise in temperature and moisture content at the intakes of the downstream tower. The increase in the tower spacing, in general, contributes to a decrease in air temperature at the intakes of the downstream tower. However, at low crosswind speed, the heat transfer at the intakes can rise with the tower spacing due to a reduction in the protection possibilities of the upstream tower. Results of the numerical simulation of airflow around three cooling towers indicated that the increase in the number of cooling towers contributes to a rise in temperature and moisture content at the intakes. Full article

(This article belongs to the Special Issue Fluid Flows in Geotechnical Engineering)

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6 pages, 753 KiB

Open AccessArticle

Electrically Induced Hydrodynamic Effect in Nematics Caused by Volume Reduction

by Maksim Sargsyan

Fluids 2022, 7(10), 316; https://doi.org/10.3390/fluids7100316 - 26 Sep 2022

Viewed by 1397

Abstract

A pressure gradient caused by the local field-induced reduction of the effective molecular volume results in a flow of the nematic liquid crystal (NLC). Here, the hydrodynamics of homeotropically aligned NLC molecules under the influence of this pressure gradient was studied theoretically. The [...] Read more.

A pressure gradient caused by the local field-induced reduction of the effective molecular volume results in a flow of the nematic liquid crystal (NLC). Here, the hydrodynamics of homeotropically aligned NLC molecules under the influence of this pressure gradient was studied theoretically. The equations describing the system were written and solved in the steady-state case using analytical methods, and the stationary velocity of the observed flow was found. We discussed the obtained results and compared them with existing experimental results. Full article

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18 pages, 3884 KiB

Open AccessArticle

Calibration and Verification of Operation Parameters for an Array of Vectrino Profilers Configured for Turbulent Flow Field Measurement around Bridge Piers—Part I

by Gordon Gilja, Robert Fliszar, Antonija Harasti and Manousos Valyrakis

Fluids 2022, 7(10), 315; https://doi.org/10.3390/fluids7100315 - 23 Sep 2022

Cited by 2 | Viewed by 1947

Abstract

Flow mapping around bridge piers is crucial in estimating scour development potential under different flow conditions. The reliable measurement of turbulence and the estimation of Reynolds stress can be achieved on scaled models under controlled laboratory experiments using high-frequency Acoustic Doppler Velocimeter Profilers [...] Read more.

Flow mapping around bridge piers is crucial in estimating scour development potential under different flow conditions. The reliable measurement of turbulence and the estimation of Reynolds stress can be achieved on scaled models under controlled laboratory experiments using high-frequency Acoustic Doppler Velocimeter Profilers (ADVP) for flow measurement. The aim of this paper was to obtain operation parameters for an array of Vectrino Profilers for turbulent flow field measurement to reliably measure the flow field around bridge piers. Laboratory experiments were conducted on a scaled river model set up in an open channel hydraulic flume. Flow field data were measured on three characteristic profiles, each containing five measurement points collected by ADVPs configured as an array of two instruments. The determination of the operation parameters was done as a two-step process—calibration through the flume’s pump flow rate and verification with Acoustic Doppler Current Profiler RioGrande field data. Based on the results, the following setup for ADVPs’ operation parameters can be used to obtain reliable flow data in the scour hole next to the bridge pier: adaptive Ping Algorithm, Transmit Pulse Size of 4 mm and Cell Size of 1 mm. Full article

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15 pages, 4800 KiB

Open AccessArticle

Experience of Patient-Specific CFD Simulation of Blood Flow in Proximal Anastomosis for Femoral-Popliteal Bypass

by Yana Ivanova, Andrey Yukhnev, Ludmila Tikhomolova, Evgueni Smirnov, Andrey Vrabiy, Andrey Suprunovich, Alexey Morozov, Gennady Khubulava and Valery Vavilov

Fluids 2022, 7(10), 314; https://doi.org/10.3390/fluids7100314 - 21 Sep 2022

Cited by 3 | Viewed by 4155

Abstract

Femoral artery bypass surgery needs postoperative monitoring due to the high complication risks after bypass. Numerical simulation is an effective tool to help solve this task. This work presents the experience of patient-specific CFD simulation of blood flow in proximal anastomosis for femoral-popliteal [...] Read more.

Femoral artery bypass surgery needs postoperative monitoring due to the high complication risks after bypass. Numerical simulation is an effective tool to help solve this task. This work presents the experience of patient-specific CFD simulation of blood flow in proximal anastomosis for femoral-popliteal bypass, including patient follow-up after bypass surgery. Six cases of proximal anastomosis of femoral-popliteal bypass 3–30 months after surgery were studied. A repeated study was performed for four patients to monitor geometric and hemodynamic changes. The blood flow structure variety in proximal anastomoses and the blood flow dynamics during the cardiac cycle are described in detail using CFD simulation. Special attention is paid to time-average wall shear stresses (TAWSS) and oscillatory shear index (OSI) distributions. Low and oscillatory wall shear stresses were registered in the graft downstream from the suture, especially in case of low inlet flow. It was shown that the postoperative geometry changes led to significant hemodynamic changes; thereby, neointima has grown in areas with initially low and oscillatory wall shear stresses. Full article

(This article belongs to the Special Issue Cardiovascular Hemodynamics)

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Fluids, Volume 7, Issue 10 (October 2022) – 25 articles

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