Fluids

17 pages, 3933 KiB

Open AccessArticle

Influence of the Deposition Rate and Substrate Temperature on the Morphology of Thermally Evaporated Ionic Liquids

by Rita M. Carvalho, Cândida Neto, Luís M. N. B. F. Santos, Margarida Bastos and José C. S. Costa

Fluids 2023, 8(3), 105; https://doi.org/10.3390/fluids8030105 - 22 Mar 2023

Cited by 1 | Viewed by 1668

The wetting behavior of ionic liquids (ILs) on the mesoscopic scale considerably impacts a wide range of scientific fields and technologies. Particularly under vacuum conditions, these materials exhibit unique characteristics. This work explores the effect of the deposition rate and substrate temperature on [...] Read more.

The wetting behavior of ionic liquids (ILs) on the mesoscopic scale considerably impacts a wide range of scientific fields and technologies. Particularly under vacuum conditions, these materials exhibit unique characteristics. This work explores the effect of the deposition rate and substrate temperature on the nucleation, droplet formation, and droplet spreading of ILs films obtained by thermal evaporation. Four ILs were studied, encompassing an alkylimidazolium cation (C_nC₁im) and either bis(trifluoromethylsulfonyl)imide (NTf₂) or the triflate (OTf) as the anion. Each IL sample was simultaneously deposited on surfaces of indium tin oxide (ITO) and silver (Ag). The mass flow rate was reproducibly controlled using a Knudsen cell as an evaporation source, and the film morphology (micro- and nanodroplets) was evaluated by scanning electron microscopy (SEM). The wettability of the substrates by the ILs was notably affected by changes in mass flow rate and substrate temperature. Specifically, the results indicated that an increase in the deposition rate and/or substrate temperature intensified the droplet coalescence of [C₂C₁im][NTf₂] and [C₂C₁im][OTf] on ITO surfaces. Conversely, a smaller impact was observed on the Ag surface due to the strong adhesion between the ILs and the metallic film. Furthermore, modifying the deposition parameters resulted in a noticeable differentiation in the droplet morphology obtained for [C₈C₁im][NTf₂] and [C₈C₁im][OTf]. Nevertheless, droplets from long-chain ILs deposited on ITO surfaces showed intensified coalescence, regardless of the deposition rate or substrate temperature. Full article

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

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Graphical abstract

13 pages, 3438 KiB

Open AccessArticle

Validation of the LOGOS Software Package Methods for the Numerical Simulation of Cavitational Flows

by Andrey Kozelkov, Andrey Kurkin, Vadim Kurulin, Kseniya Plygunova and Olga Krutyakova

Fluids 2023, 8(3), 104; https://doi.org/10.3390/fluids8030104 - 22 Mar 2023

Cited by 3 | Viewed by 951

Abstract

Verification problems and numeric simulation of cavitation processes with the help of LOGOS computational fluid dynamics software are presented in this article. The Volume of Fluid method realized within LOGOS allowing numerical simulation of double-phase problems with a free surface is used for [...] Read more.

Verification problems and numeric simulation of cavitation processes with the help of LOGOS computational fluid dynamics software are presented in this article. The Volume of Fluid method realized within LOGOS allowing numerical simulation of double-phase problems with a free surface is used for numeric simulation. Cavitation is resolved by updating the method with the account for interphase mass exchange; its condensation and evaporation parameters are calculated with the use of the Schnerr–Sauer and Zwart–Gerber–Belamri cavitation models. Numerical simulation results of most actual test problems considering turbulence and having reliable numerical data are presented, including simulations of flow around cylinders with flat and hemispherical end surfaces for various cavitation numbers. Numerical simulation results are presented for the process of rotation of a VP1304 screw propeller in the cavitational mode. Numerical experiments prove the operability of the implemented method. Full article

(This article belongs to the Special Issue Advances in Numerical Methods for Computational Fluid Dynamics With Open-Source Software)

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40 pages, 802 KiB

Open AccessArticle

Analysis of Hierarchical Grid Refinement Techniques for the Lattice Boltzmann Method by Numerical Experiments

by Alexander Schukmann, Andreas Schneider, Viktor Haas and Martin Böhle

Fluids 2023, 8(3), 103; https://doi.org/10.3390/fluids8030103 - 21 Mar 2023

Cited by 1 | Viewed by 2019

Abstract

Over the last few decades, several grid coupling techniques for hierarchically refined Cartesian grids have been developed to provide the possibility of varying mesh resolution in lattice Boltzmann methods. The proposed schemes can be roughly categorized based on the individual grid transition interface [...] Read more.

Over the last few decades, several grid coupling techniques for hierarchically refined Cartesian grids have been developed to provide the possibility of varying mesh resolution in lattice Boltzmann methods. The proposed schemes can be roughly categorized based on the individual grid transition interface layout they are adapted to, namely cell-vertex or cell-centered approaches, as well as a combination of both. It stands to reason that the specific properties of each of these grid-coupling algorithms influence the stability and accuracy of the numerical scheme. Consequently, this naturally leads to a curiosity regarding the extent to which this is the case. The present study compares three established grid-coupling techniques regarding their stability ranges by conducting a series of numerical experiments for a square duct flow, including various collision models. Furthermore the hybrid-recursive regularized collision model, originally introduced for cell-vertex algorithms with co-located coarse and fine grid nodes, has been adapted to cell-centered and combined methods. Full article

(This article belongs to the Topic Computational Fluid Dynamics (CFD) and Its Applications)

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14 pages, 9485 KiB

Open AccessArticle

Flow Boiling Heat Transfer Performance and Boiling Phenomena on Various Straight Fin Configurations

by Indro Pranoto, Muhammad Aulia Rahman, Cahya Dhika Wicaksana, Alan Eksi Wibisono, Fauzun and Arif Widyatama

Fluids 2023, 8(3), 102; https://doi.org/10.3390/fluids8030102 - 20 Mar 2023

Viewed by 1613

Abstract

The trend of miniaturisation in recent decades has led to the development of compact electronic devices. The reduction in the required dimension leads to the exponential rise in the heat flux dissipated from such a system. A proper thermal management system is necessary [...] Read more.

The trend of miniaturisation in recent decades has led to the development of compact electronic devices. The reduction in the required dimension leads to the exponential rise in the heat flux dissipated from such a system. A proper thermal management system is necessary to keep the temperature of a computer chip’s junction within acceptable limits and maintain its performance. Flow boiling modification using straight fins in microchannels has proven to be an effective passive enhancement of the cooling system. The core interest of this research is figuring out the optimal configuration of the fin shapes and configurations. Hence, it is crucial to gain a comprehensive understanding of the flow boiling phenomenon to establish a more general approach. In this study, the boiling heat transfer performance of fin microchannels with various shapes and dimensions is investigated experimentally. The study has shown that the choice of fin geometry has a significant impact on the thermal performance of a heat transfer system. Specifically, the results indicate that a rectangular cross-section fin performs better than a trapezoidal one with the same fin gap. The rectangular cross-section fin exhibits the highest heat transfer coefficient of 5066.84 W/m²∙K, outperforming the trapezoidal fin in terms of heat transfer capability. As the hydraulic diameter reduces, the thermal boundary layer becomes denser, providing a more distributed saturated region. This leads to the increase in the heat transfer coefficient up to 22.5% and 17.1% for rectangular and trapezoidal fins, respectively. Additionally, the efficiency analysis shows that, albeit increasing the mass flux and reducing the gap increase the average cooling performance, but the pressure drop jumps up to 48%, reducing the efficiency of the heat removal system. Full article

(This article belongs to the Topic Applied Heat Transfer)

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9 pages, 508 KiB

Open AccessArticle

Turbulence via Intermolecular Potential: Viscosity and Transition Range of the Reynolds Number

by Rafail V. Abramov

Fluids 2023, 8(3), 101; https://doi.org/10.3390/fluids8030101 - 18 Mar 2023

Cited by 2 | Viewed by 2278

Abstract

Turbulence in fluids is an ubiquitous phenomenon, characterized by spontaneous transition of a smooth, laminar flow to rapidly changing, chaotic dynamics. In 1883, Reynolds experimentally demonstrated that, in an initially laminar flow of water, turbulent motions emerge without any measurable external disturbance. To [...] Read more.

Turbulence in fluids is an ubiquitous phenomenon, characterized by spontaneous transition of a smooth, laminar flow to rapidly changing, chaotic dynamics. In 1883, Reynolds experimentally demonstrated that, in an initially laminar flow of water, turbulent motions emerge without any measurable external disturbance. To this day, turbulence remains a major unresolved phenomenon in fluid mechanics; in particular, there is a lack of a mathematical model where turbulent dynamics emerge naturally from a laminar flow. Recently, we proposed a new theory of turbulence in gases, according to which turbulent motions are created in an inertial gas flow by the mean field effect of the intermolecular potential. In the current work, we investigate the effect of viscosity in our turbulence model by numerically simulating the air flow at normal conditions in a straight pipe for different values of the Reynolds number. We find that the transition between laminar and turbulent flow in our model occurs, without any deliberate perturbations, as the Reynolds number increases from 2000 to 4000. As the simulated flow becomes turbulent, the decay rate of the time averaged Fourier spectrum of the kinetic energy in our model approaches Kolmogorov’s inverse five-thirds law. Both results are consistent with experiments and observations. Full article

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

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23 pages, 6128 KiB

Open AccessReview

A Review of Preconditioning and Artificial Compressibility Dual-Time Navier–Stokes Solvers for Multiphase Flows

by Van-Tu Nguyen and Warn-Gyu Park

Fluids 2023, 8(3), 100; https://doi.org/10.3390/fluids8030100 - 16 Mar 2023

Cited by 1 | Viewed by 1800

Abstract

This review paper aims to summarize recent advancements in time-marching schemes for solving Navier–Stokes (NS) equations in multiphase flow simulations. The focus is on dual-time stepping, local preconditioning, and artificial compressibility methods. These methods have proven to be effective in achieving high time [...] Read more.

This review paper aims to summarize recent advancements in time-marching schemes for solving Navier–Stokes (NS) equations in multiphase flow simulations. The focus is on dual-time stepping, local preconditioning, and artificial compressibility methods. These methods have proven to be effective in achieving high time accuracy in simulations, as well as converting the incompressible NS equations into a hyperbolic form that can be solved using compact schemes, thereby accelerating the solution convergence and allowing for the simulation of compressible flows at all Mach numbers. The literature on these methods continues to grow, providing a deeper understanding of the underlying physical processes and supporting technological advancements. This paper also highlights the imposition of dual-time stepping on both incompressible and compressible NS equations. This paper provides an updated overview of advanced methods for the CFD community to continue developing methods and select the most suitable two-phase flow solver for their respective applications. Full article

(This article belongs to the Special Issue Numerical Modeling and Experimental Studies of Two-Phase Flows)

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28 pages, 13063 KiB

Open AccessArticle

Simulation of Particulate Matter Structure Detachment from Surfaces of Wall-Flow Filters for Elevated Velocities Applying Lattice Boltzmann Methods

by Nicolas Hafen, Jan E. Marquardt, Achim Dittler and Mathias J. Krause

Fluids 2023, 8(3), 99; https://doi.org/10.3390/fluids8030099 - 10 Mar 2023

Cited by 2 | Viewed by 1279

Abstract

Rearrangement events in wall-flow filters lead to the formation of specific deposition patterns, which affect a filter’s pressure drop, its loading capacity and the separation efficiency. A universal and consistent formulation of probable causes and influence factors does not exist and appropriate calculation [...] Read more.

Rearrangement events in wall-flow filters lead to the formation of specific deposition patterns, which affect a filter’s pressure drop, its loading capacity and the separation efficiency. A universal and consistent formulation of probable causes and influence factors does not exist and appropriate calculation models that enable a quantification of respective influence factors are missing. In this work, a previously developed lattice Boltzmann method, which has been used with inflow velocities of up to

2 {m s}^{- 1}

, is applied to elevated velocities of up to

60 {m s}^{- 1}

. The particle-free flow, a single layer fragment and a deposition layer during break-up are investigated as three different scenarios. One goal of this work is a comprehensive quantification of the stability and accuracy of both particle-free and particle-including flows, considering static, impermeable deposition-layer fragments. A second goal is the determination of the hydrodynamic surface forces and the deduction of the local detachment likelihood of individual layer fragments. Satisfactory stability and accuracy can be shown for fluid velocity, fluid pressure and the hydrodynamic forces. When considering layer fragments, the parameter domain turns out to be limited to inflow velocities of

28 {m s}^{- 1}

. It is shown that fragment detachment rather occurs consecutively and regions of no possible detachment are identified. The work contributes to an understanding of rearrangement events and respective deposition pattern predictions and enables potential optimizations in engine performance, fuel consumption and the service life of wall-flow filters. Full article

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23 pages, 14241 KiB

Open AccessArticle

Control of Chemoconvection in a Rectangular Slot by Changing Its Spatial Orientation

by Elena Mosheva, Ramil Siraev and Dmitry Bratsun

Fluids 2023, 8(3), 98; https://doi.org/10.3390/fluids8030098 - 09 Mar 2023

Viewed by 963

Abstract

Recently, we found that a two-layer miscible system placed in a vertical slab reactor shows an occurrence of a density shock-wave-like pattern. This wave resembles a turbulent bore separating immobile fluid and an area of intense mixing. It travels away from the convective [...] Read more.

Recently, we found that a two-layer miscible system placed in a vertical slab reactor shows an occurrence of a density shock-wave-like pattern. This wave resembles a turbulent bore separating immobile fluid and an area of intense mixing. It travels away from the convective core of the system and is highly dependent on the intensity of a gravity-dependent chemoconvection in the cocurrent flow. The novelty of this work is that we demonstrate that the change in angle between gravity and wave direction allows controlling the chemoconvection intensity and, consequently, the rate of a spatially-extended reaction. We study both experimentally and numerically the effect of the spatial orientation of a slab reactor to a gravity field on a flow structure induced by a neutralization reaction. In experiments, we use aqueous mixtures of nitric acid and sodium hydroxide. We apply the Fizeau interferometry to visualize the flow and use the PIV method to measure the fluid velocity. The mathematical model includes reaction–diffusion–convection equations that describe 3D flows. We study the flow modifications with a change in the inclination angle from 0 to 90 degrees. At small angles (up to 30), the cocurrent flow becomes spatially heterogeneous, and the fields of salt and acid are separated. If the inclination exceeds 50 degrees, the wavefront is deformed, and the wave breaks up, resulting in a sharp decrease in the reaction rate. Full article

(This article belongs to the Section Heat and Mass Transfer)

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16 pages, 4582 KiB

Open AccessBrief Report

Comparison of Mean Properties of Turbulent Pipe and Channel Flows at Low-to-Moderate Reynolds Numbers

by Carmine Di Nucci and Rafik Absi

Fluids 2023, 8(3), 97; https://doi.org/10.3390/fluids8030097 - 08 Mar 2023

Cited by 2 | Viewed by 1601

Abstract

We focus on the fully developed turbulent flow in circular pipes and channels. We provide a comparison of the mean velocity profiles, and we compute the values of the global indicators, such as the skin friction, the mean velocity, the centerline velocity, the [...] Read more.

We focus on the fully developed turbulent flow in circular pipes and channels. We provide a comparison of the mean velocity profiles, and we compute the values of the global indicators, such as the skin friction, the mean velocity, the centerline velocity, the displacement thickness, and the momentum thickness. The comparison is done at low-to-moderate Reynolds numbers. For channel flow, we deduced the mean velocity profiles using an indirect turbulent model; for pipe flow, we extracted the needed information from a direct numerical simulation database available in the open literature. A one-to-one comparison of these values at identical Reynolds numbers provides a deep insight into the difference between pipe and channel flows. This line of reasoning allows us to highlight some deviations among the mean velocity profiles extracted from different pipe databases. Full article

(This article belongs to the Special Issue Turbulent Flow, 2nd Edition)

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20 pages, 7411 KiB

Open AccessArticle

Numerical Analysis of Linear Traveling Wave in Rotating Rayleigh–Bénard Convection with an Adiabatic Sidewall

by Toshio Tagawa

Fluids 2023, 8(3), 96; https://doi.org/10.3390/fluids8030096 - 08 Mar 2023

Viewed by 1328

Abstract

In rotating Rayleigh–Bénard problems, convection with traveling waves may occur near the sidewalls. The Rayleigh number, Taylor number and Prandtl number are involved in this phenomenon, and the convection mode is determined depending on their values. We focused on the onset of this [...] Read more.

In rotating Rayleigh–Bénard problems, convection with traveling waves may occur near the sidewalls. The Rayleigh number, Taylor number and Prandtl number are involved in this phenomenon, and the convection mode is determined depending on their values. We focused on the onset of this convection with traveling waves under the assumption that centrifugal force is neglected. By conducting two-dimensional linear stability analyses assuming periodicity of the flow and temperature fields along the sidewall direction, we investigated the effect of the Taylor number and the Prandtl number on the critical Rayleigh number and also attempted to understand the phenomenon qualitatively through three-dimensional visualizations. It was exhibited that as the Taylor number increases, the wave number, the Rayleigh number and the phase speed are found to increase. On the other hand, as the Prandtl number decreases, the wavenumber and the Rayleigh number decrease, but the phase velocity increases. The present analyses suggest that convection modes localized near the sidewalls are unlikely to emerge for low Prandtl number cases, which are comparable to those of liquid metals. Full article

(This article belongs to the Section Heat and Mass Transfer)

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18 pages, 454 KiB

Open AccessArticle

Modelling and Simulation of Heat Exchanger with Strong Dependence of Oil Viscosity on Temperature

by Dinara Kurmanova, Nurbolat Jaichibekov, Anton Karpenko and Konstantin Volkov

Fluids 2023, 8(3), 95; https://doi.org/10.3390/fluids8030095 - 08 Mar 2023

Cited by 1 | Viewed by 2925

Abstract

The heating of oil and oil products is widely used to reduce energy losses during transportation. An approach is developed to determine the effective length of the heat exchanger and the temperature of the cold coolant (oil) at its outlet in the case [...] Read more.

The heating of oil and oil products is widely used to reduce energy losses during transportation. An approach is developed to determine the effective length of the heat exchanger and the temperature of the cold coolant (oil) at its outlet in the case of a strong dependence of oil viscosity on temperature. Oil from the Uzen field (Kazakhstan) is considered as a heated coolant, and water is considered as a heating component. The method of the log–mean temperature difference, modified for the case of variable viscosity, and the methods of computational fluid dynamics (CFD) are used for calculations. The results of the numerical calculations are compared with the data obtained on the basis of a theoretical approach at a constant viscosity. When using a theoretical approach with a constant or variable viscosity, the heat transfer coefficients to cold and hot coolants are found using criterion dependencies. The Reynolds-averaged Navier–Stokes (RANS) and a turbulence model that takes into account the laminar–turbulent transition are applied. In the case of variable oil viscosity, a transition from the laminar flow regime to the turbulent one is manifested, which has a significant effect on the effective length of the heat exchanger. The obtained results of the CFD calculations are of interest for the design of heat exchangers of a new type, for example, helicoid ones. Full article

(This article belongs to the Topic Applied Heat Transfer)

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17 pages, 1806 KiB

Open AccessArticle

On the Determination of the 3D Velocity Field in Terms of Conserved Variables in a Compressible Ocean

by Rémi Tailleux

Fluids 2023, 8(3), 94; https://doi.org/10.3390/fluids8030094 - 08 Mar 2023

Viewed by 1341

Abstract

Explicit expressions of the 3D velocity field in terms of the conserved quantities of ideal fluid thermocline theory, namely the Bernoulli function, density, and potential vorticity, are generalised in this paper to a compressible ocean with a realistic nonlinear equation of state. The [...] Read more.

Explicit expressions of the 3D velocity field in terms of the conserved quantities of ideal fluid thermocline theory, namely the Bernoulli function, density, and potential vorticity, are generalised in this paper to a compressible ocean with a realistic nonlinear equation of state. The most general such expression is the ‘inactive wind’ solution, an exact nonlinear solution of the inviscid compressible Navier–Stokes equation that satisfies the continuity equation as a consequence of Ertel’s potential vorticity theorem. However, due to the non-uniqueness of the choice of the Bernoulli function, such expressions are not unique and primarily differ in the magnitude of their vertical velocity component. Due to the thermobaric nonlinearity of the equation of state, the expression for the 3D velocity field of a compressible ocean is found to resemble its ideal fluid counterpart only if constructed using the available form of the Bernoulli function, the Bernoulli equivalent of Lorenz’s available potential energy (APE). APE theory also naturally defines a quasi-material, approximately neutral density variable known as the Lorenz reference density. This density variable, in turn, defines a potential vorticity variable that is minimally affected by thermobaric production, thus providing all the necessary tools for extending most results of ideal fluid thermocline theory to a compressible ocean. Full article

(This article belongs to the Collection Geophysical Fluid Dynamics)

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19 pages, 7721 KiB

Open AccessArticle

Control of MHD Flow and Heat Transfer of a Micropolar Fluid through Porous Media in a Horizontal Channel

by Miloš Kocić, Živojin Stamenković, Jelena Petrović and Jasmina Bogdanović-Jovanović

Fluids 2023, 8(3), 93; https://doi.org/10.3390/fluids8030093 - 08 Mar 2023

Cited by 5 | Viewed by 1366

Abstract

The problem considered in this paper is a steady micropolar fluid flow in porous media between two plates. This model can be used to describe the flow of some types of fluids with microstructures, such as human and animal blood, muddy water, colloidal [...] Read more.

The problem considered in this paper is a steady micropolar fluid flow in porous media between two plates. This model can be used to describe the flow of some types of fluids with microstructures, such as human and animal blood, muddy water, colloidal fluids, lubricants and chemical suspensions. Fluid flow is a consequence of the constant pressure gradient along the flow, while two parallel plates are fixed and have different constant temperatures during the fluid flow. Perpendicular to the flow, an external magnetic field is applied. General equations of the problem are reduced to ordinary differential equations and solved in the closed form. Solutions for velocity, microrotation and temperature are used to explain the influence of the external magnetic field (Hartmann number), the characteristics of the micropolar fluid (coupling and spin gradient viscosity parameter) and the characteristics of the porous medium (porous parameter) using graphs. The results obtained in the paper show that the increase in the additional viscosity of micropolar fluids emphasizes the microrotation vector. Moreover, the analysis of the effect of the porosity parameter shows how the permeability of a porous medium can influence the fluid flow and heat transfer of a micropolar fluid. Finally, it is shown that the influence of the external magnetic field reduces the characteristics of micropolar fluids and tends to reduce the velocity field and make it uniform along the cross-section of the channel. Full article

(This article belongs to the Special Issue Focus on Supercritical Fluids: Control and Extraction)

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23 pages, 9119 KiB

Open AccessArticle

Detection and Recognition of the Underwater Object with Designated Features Using the Technical Stereo Vision System

by Vadim Kramar, Aleksey Kabanov, Oleg Kramar, Sergey Fateev and Valerii Karapetian

Fluids 2023, 8(3), 92; https://doi.org/10.3390/fluids8030092 - 07 Mar 2023

Cited by 2 | Viewed by 1211

Abstract

The article discusses approaches to solving the problems of detecting, recognizing, and localizing an object with given distinctive features in an aquatic environment using a technical stereo vision system, taking into account restrictions. The stereo vision system is being developed as part of [...] Read more.

The article discusses approaches to solving the problems of detecting, recognizing, and localizing an object with given distinctive features in an aquatic environment using a technical stereo vision system, taking into account restrictions. The stereo vision system is being developed as part of the task in which the AUV, for the purpose of conducting a monitoring mission, follows from the starting point of its route along a given trajectory in order to detect and classify an object with known characteristics and determine its coordinates using a technical stereo vision system at a distance up to 5 m from it with appropriate water clarity. The developed program for the system of the technical stereo vision should provide the AUV with the following information: video sequence; a frame with an image of the detected object; previously unknown characteristics of the object if it is possible to detect them (color, size or shape); distance to the object from the technical stereo vision system; and linear coordinates relative to the technical stereo vision system. Testing of the developed software was carried out on the operating module of the stereo vision installed on the AUV in the underbody compartment. The study was carried out in the pool and in open water. The experiments performed have shown the effectiveness of the developed system when used in conjunction with an underwater robot. Full article

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41 pages, 1477 KiB

Open AccessReview

Computational Fluid Dynamics Modelling of Two-Phase Bubble Columns: A Comprehensive Review

by Giorgio Besagni, Nicolò Varallo and Riccardo Mereu

Fluids 2023, 8(3), 91; https://doi.org/10.3390/fluids8030091 - 03 Mar 2023

Cited by 6 | Viewed by 4497

Abstract

Bubble columns are used in many different industrial applications, and their design and characterisation have always been very complex. In recent years, the use of Computational Fluid Dynamics (CFD) has become very popular in the field of multiphase flows, with the final goal [...] Read more.

Bubble columns are used in many different industrial applications, and their design and characterisation have always been very complex. In recent years, the use of Computational Fluid Dynamics (CFD) has become very popular in the field of multiphase flows, with the final goal of developing a predictive tool that can track the complex dynamic phenomena occurring in these types of reactors. For this reason, we present a detailed literature review on the numerical simulation of two-phase bubble columns. First, after a brief introduction to bubble column technology and flow regimes, we discuss the state-of-the-art modelling approaches, presenting the models describing the momentum exchange between the phases (i.e., drag, lift, turbulent dispersion, wall lubrication, and virtual mass forces), Bubble-Induced Turbulence (BIT), and bubble coalescence and breakup, along with an overview of the Population Balance Model (PBM). Second, we present different numerical studies from the literature highlighting different model settings, performance levels, and limitations. In addition, we provide the errors between numerical predictions and experimental results concerning global (gas holdup) and local (void fraction and liquid velocity) flow properties. Finally, we outline the major issues to be solved in future studies. Full article

(This article belongs to the Special Issue Gas–Liquid Contactors: New Theoretical and Experimental Approaches for Their Better Understanding)

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17 pages, 1607 KiB

Open AccessArticle

Prediction of Critical Heat Flux of Mixtures Flowing in Channels

by Mirza M. Shah

Fluids 2023, 8(3), 90; https://doi.org/10.3390/fluids8030090 - 02 Mar 2023

Viewed by 1190

Abstract

Boiling of mixtures in channels is involved in many chemical processes, and refrigerant mixtures are finding a rapidly increasing use in the refrigeration industries. Hence, reliable prediction of CHF (critical heat flux) is needed. There is no published method that has been verified [...] Read more.

Boiling of mixtures in channels is involved in many chemical processes, and refrigerant mixtures are finding a rapidly increasing use in the refrigeration industries. Hence, reliable prediction of CHF (critical heat flux) is needed. There is no published method that has been verified over a wide range of parameters. In this study, available data for CHF in tubes and annuli were compared to general correlations for tubes and annuli, which are well-verified for single-component fluids. This paper presents the results of this comparison. It was found that general correlations for single-component fluids were in satisfactory agreement with data for mixtures. The data included mixtures of refrigerants and chemicals, reduced pressure 0.02 to 0.8597, mass flux 200 to 3798 kgm⁻²s⁻¹, temperature glide 2.1 to 21.9 K, and critical quality −0.46 to 0.99. The data for annuli were predicted with a MAD (mean absolute deviation) of 13.6%, and the data for tubes had a MAD of 13.9% when compared to the Shah correlations for single-component fluids. Based on the results of the present data analysis and results of research on pool boiling, a range is identified in which pure fluid correlations can be used for mixtures. This will be useful in the design of heat exchangers involving the boiling of mixtures in channels. Full article

(This article belongs to the Section Heat and Mass Transfer)

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13 pages, 1899 KiB

Open AccessArticle

Horizontal Stratified Air–Foam–Water Flows: Preliminary Modelling Attempts with OLGA

by William Ferretto, Igor Matteo Carraretto, Andrea Tiozzo, Marco Montini and Luigi Pietro Maria Colombo

Fluids 2023, 8(3), 89; https://doi.org/10.3390/fluids8030089 - 01 Mar 2023

Cited by 2 | Viewed by 1275

Abstract

Water accumulation is a major problem in the flow assurance of gas pipelines. To limit liquid loading issues, deliquification by means of surfactant injection is a promising alternative to the consolidated mechanical methods. However, the macroscopic behavior of foam pipe flow in the [...] Read more.

Water accumulation is a major problem in the flow assurance of gas pipelines. To limit liquid loading issues, deliquification by means of surfactant injection is a promising alternative to the consolidated mechanical methods. However, the macroscopic behavior of foam pipe flow in the presence of other phases has barely been explored. The goal of this work was to propose an approach to simulate air–water–foam flows in horizontal pipes using OLGA by Schlumberger, an industry standard tool for the transient simulation of multiphase flow. The simulation results were compared with experimental data for 60 mm and 30 mm ID (Inner Diameter) horizontal pipelines. Preliminary validation for two-phase air–water flow was carried out, which showed that correct flow pattern recognition is essential to accurately reproduce the experimental data. Then, stratified air–foam–water flows were investigated, assuming different models for the foam local velocity distribution. Foam rheology was considered through the Herschel–Bulkley model with the yield stress varying in time due to foam decay. The results showed good agreement for a uniform velocity profile and fresh foam properties in the case of the 60 mm ID pipeline, whereas for the 30 mm ID, which was characterized by significantly higher velocities, a linear velocity profile and 2000 s foam aging provided the best agreement. In both cases, the pressure gradient was overestimated, and the mean absolute prediction error ranged from about 5% to 30%. Full article

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

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17 pages, 1841 KiB

Open AccessArticle

Conjugate Heat Transfer in Thermal Inkjet Printheads

by S. G. Mallinson, G. D. McBain and B. R. Brown

Fluids 2023, 8(3), 88; https://doi.org/10.3390/fluids8030088 - 01 Mar 2023

Cited by 1 | Viewed by 1368

Abstract

The mass of individual droplets ejected from a thermal inkjet printhead increases with increasing local temperature near the ejector nozzles. The amount of ink deposited on the page and so the printed image density depends on the droplet mass. Thus, printhead temperature nonuniformity [...] Read more.

The mass of individual droplets ejected from a thermal inkjet printhead increases with increasing local temperature near the ejector nozzles. The amount of ink deposited on the page and so the printed image density depends on the droplet mass. Thus, printhead temperature nonuniformity results in printed image density variations that can be unacceptable to the end users of the printed output. Such temperature variations arise from a combination of the ink fluid flow and the heat transfer in both the ink and the solid components in the printhead. Conjugate heat transfer (CHT) in thermal inkjet printheads is investigated here using validated numerical simulations. A typical thermal inkjet printhead is considered here for the first time, with cold ink drawn through the solid structural components by the ejector nozzle refill. The effect of the width of the feedhole above the printhead chip on the temperature field within the chip is analyzed. Validation of the simulation model required the derivation of novel analytical solutions for the relatively simple problems of fully developed forced convection in a differentially heated planar channel and conduction against convection in plug flow. The results from numerical simulations of these two problems are found to compare well with the newly derived analytical solutions. CHT in flow over a backward-facing step with a heated downstream wall was also simulated as part of the validation process, and good agreement was observed with earlier numerical studies. For the main part of the study, it was found that increasing the width of the feedhole reduces the gradients in temperature on the surface of the printhead chip, thus reducing temperature-related printing defects. Full article

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10 pages, 7655 KiB

Open AccessArticle

Improving Homogeneity of 3D-Printed Cementitious Material Distribution for Radial Toolpath

by Mingyang Li, Zhixin Liu, Jin Yao Ho and Teck Neng Wong

Fluids 2023, 8(3), 87; https://doi.org/10.3390/fluids8030087 - 01 Mar 2023

Viewed by 1189

Abstract

The 3D cementitious material printing method is an extrusion-based additive manufacturing strategy in which cementitious materials are extruded through a dynamic nozzle system to form filaments. Despite its ability to fabricate structures with high complexity and efficiency, the uneven material distribution during the [...] Read more.

The 3D cementitious material printing method is an extrusion-based additive manufacturing strategy in which cementitious materials are extruded through a dynamic nozzle system to form filaments. Despite its ability to fabricate structures with high complexity and efficiency, the uneven material distribution during the extrusion and deposition process is often encountered when a radial toolpath is introduced. This limits the design freedom and printing parameters that can be utilized during radial toolpath printing. Here, we report a facile strategy to overcome the existing challenges of cementitious material non-homogeneity by rationally developing new nozzle geometries that passively compensate the differential deposition rate encountered in conventional rectangular nozzles. Using two-phase numerical study, we showed that our strategy has the potential of achieving a homogeneous mass distribution even when the nozzle travel speed is unfavorably high, while filament from a rectangular nozzle remains highly non-homogenous. The material distribution unevenness can be reduced from 1.35 to 1.23 and to 0.98 after adopting trapezoid and gaussian nozzles, indicating improvements of 34.3% and 94.2%, respectively. This work not only outlines the methodology for improving the quality of corner/curved features in 3DCMP, but also introduces a new strategy which can be adopted for other extrusion-based fabrication techniques with high material inertia. Full article

(This article belongs to the Special Issue Advances in Computational Mechanics of Non-Newtonian Fluids)

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28 pages, 34090 KiB

Open AccessArticle

A Highly Scalable Direction-Splitting Solver on Regular Cartesian Grid to Compute Flows in Complex Geometries Described by STL Files

by Antoine Morente, Aashish Goyal and Anthony Wachs

Fluids 2023, 8(3), 86; https://doi.org/10.3390/fluids8030086 - 28 Feb 2023

Cited by 5 | Viewed by 1524

Abstract

We implement the Direction-Splitting solver originally proposed by Keating and Minev in 2013 and allow complex geometries to be described by a triangulation defined in STL files. We develop an algorithm that computes intersections and distances between the regular Cartesian grid and the [...] Read more.

We implement the Direction-Splitting solver originally proposed by Keating and Minev in 2013 and allow complex geometries to be described by a triangulation defined in STL files. We develop an algorithm that computes intersections and distances between the regular Cartesian grid and the surface triangulation using a ray-tracing method. We thoroughly validate the implementation on assorted flow configurations. Finally, we illustrate the scalability of our implementation on a test case of a steady flow through 144,327 spherical obstacles randomly distributed in a tri-periodic box at

R e = 19.2

. The grid comprises 6.8 billion cells and the computation runs on 6800 cores of a supercomputer in less than 48 h. Full article

(This article belongs to the Special Issue Advances in Numerical Methods for Multiphase Flows, Volume II)

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23 pages, 15267 KiB

Open AccessArticle

Adjoint-Based High-Fidelity Concurrent Aerodynamic Design Optimization of Wind Turbine

by Sagidolla Batay, Bagdaulet Kamalov, Dinmukhamed Zhangaskanov, Yong Zhao, Dongming Wei, Tongming Zhou and Xiaohui Su

Fluids 2023, 8(3), 85; https://doi.org/10.3390/fluids8030085 - 28 Feb 2023

Cited by 2 | Viewed by 1541

Abstract

To evaluate novel turbine designs, the wind energy sector extensively depends on computational fluid dynamics (CFD). To use CFD in the design optimization process, where lower-fidelity approaches such as blade element momentum (BEM) are more popular, new tools to increase the accuracy must [...] Read more.

To evaluate novel turbine designs, the wind energy sector extensively depends on computational fluid dynamics (CFD). To use CFD in the design optimization process, where lower-fidelity approaches such as blade element momentum (BEM) are more popular, new tools to increase the accuracy must be developed as the latest wind turbines are larger and the aerodynamics and structural dynamics become more complex. In the present study, a new concurrent aerodynamic shape optimization approach towards multidisciplinary design optimization (MDO) that uses a Reynolds-averaged Navier–Stokes solver in conjunction with a numerical optimization methodology is introduced. A multidisciplinary design optimization tool called DAFoam is used for the NREL phase VI turbine as a baseline geometry. Aerodynamic design optimizations in terms of five different schemes, namely, cross-sectional shape, pitch angle, twist, chord length, and dihedral optimization are conducted. Pointwise, a commercial mesh generator is used to create the numerical meshes. As the adjoint approach is strongly reliant on the mesh quality, up to 17.8 million mesh cells were employed during the mesh convergence and result validation processes, whereas 2.65 million mesh cells were used throughout the design optimization due to the computational cost. The Sparse Nonlinear OPTimizer (SNOPT) is used for the optimization process in the adjoint solver. The torque in the tangential direction is the optimization’s merit function and excellent results are achieved, which shows the promising prospect of applying this approach for transient MDO. This work represents the first attempt to implement DAFoam for wind turbine aerodynamic design optimization. Full article

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18 pages, 425 KiB

Open AccessArticle

Modal Representation of Inertial Effects in Fluid–Particle Interactions and the Regularity of the Memory Kernels

by Giuseppe Procopio and Massimiliano Giona

Fluids 2023, 8(3), 84; https://doi.org/10.3390/fluids8030084 - 28 Feb 2023

Cited by 3 | Viewed by 1224

Abstract

This article develops a modal expansion (in terms of functions exponentially decaying with time) of the force acting on a micrometric particle and stemming from fluid inertial effects (usually referred to as the Basset force) deriving from the application of the time-dependent Stokes [...] Read more.

This article develops a modal expansion (in terms of functions exponentially decaying with time) of the force acting on a micrometric particle and stemming from fluid inertial effects (usually referred to as the Basset force) deriving from the application of the time-dependent Stokes equation to model fluid–particle interactions. One of the main results is that viscoelastic effects induce the regularization of the inertial memory kernels at

t = 0

, eliminating the

1 / \sqrt{t}

-singularity characterizing Newtonian fluids. The physical origin of this regularization stems from the finite propagation velocity of the internal shear stresses characterizing viscoelastic constitutive equations. The analytical expression for the fluid inertial kernel is derived for a Maxwell fluid, and a general method is proposed to obtain accurate approximations of it for generic complex viscoelastic fluids, characterized by a spectrum of relaxation times. Full article

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

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21 pages, 3604 KiB

Open AccessArticle

Experimental Comparison of Methods to Evaluate Heat Generated by Magnetic Nanofluids Exposed to Alternating Magnetic Fields

by Elisabetta Sieni, Simonetta Geninatti Crich, Maria Rosaria Ruggiero, Lucia Del Bianco, Federico Spizzo, Roberta Bertani, Mirto Mozzon, Marco Barozzi, Michele Forzan and Paolo Sgarbossa

Fluids 2023, 8(3), 83; https://doi.org/10.3390/fluids8030083 - 27 Feb 2023

Viewed by 1337

Abstract

The paper aims to compare different methods able to estimate the specific loss power (SLP) generated by three different types of magnetic nanoparticles, MNPs, dispersed in a suspension fluid, e.g., octane or water. The nanoparticles were characterized morphologically in terms of shape and [...] Read more.

The paper aims to compare different methods able to estimate the specific loss power (SLP) generated by three different types of magnetic nanoparticles, MNPs, dispersed in a suspension fluid, e.g., octane or water. The nanoparticles were characterized morphologically in terms of shape and size, chemically for composition and their physical properties like magnetization and SLP were studied. We evidenced the differences in SLP evaluation due to the applied method, particularly in the presence of thermally induced phenomena such as aggregation or precipitation of MNPs that can affect the heating curve of the samples. Then, the SLP determination methods less sensible to this phenomenon appear to be the ones that use the initial slope when the sample is in quasi-adiabatic condition. Finally, we propose a comparison of those methods based on the pros and cons of their use for the SLP determination of magnetic nanofluids. In particular, the analysis of the behavior of the heating curve is useful to evaluate the useful amplitude of the interval analysis for the initial slope methods. Full article

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15 pages, 11311 KiB

Open AccessArticle

Influence of Vertically Treaded Outsoles on Interfacial Fluid Pressure, Mass Flow Rate, and Shoe–Floor Traction during Slips

by Shubham Gupta, Subhodip Chatterjee and Arnab Chanda

Fluids 2023, 8(3), 82; https://doi.org/10.3390/fluids8030082 - 27 Feb 2023

Cited by 4 | Viewed by 1014

Abstract

Accidental injuries due to slips and falls are considered serious threats to public safety. Sufficient friction at the footwear and flooring interface is essential to reduce slip-related risks. The presence of slippery fluidic contaminants, such as water, further reduces friction and increases the [...] Read more.

Accidental injuries due to slips and falls are considered serious threats to public safety. Sufficient friction at the footwear and flooring interface is essential to reduce slip-related risks. The presence of slippery fluidic contaminants, such as water, further reduces friction and increases the risks of slip-related accidents drastically. While the effect of floorings and contaminants on footwear traction has been measured extensively across a variety of footwear designs, only a few studies have explored the science of the outsole design and its role in providing sufficient traction. In this work, the tread design of a commonly encountered outsole pattern, i.e., with vertically oriented tread channels, was parametrically altered across its width and gap. Based on the impressions of an original footwear design, nine outsoles were fabricated. The induced fluid pressures, mass flow rates, and traction were quantified by using a computational fluid dynamics (CFD) framework and through slip testing experiments. Outsoles that had wide treads with small gaps decreased the overall slipping risk on dry floorings. As compared to the tread area, tread gaps were found to be a dominating parameter in providing adequate shoe–floor traction in wet slipping conditions. The methods, including the outcomes presented in this work, are anticipated to advance the understanding of the science behind footwear friction and help footwear manufacturers optimize outsole designs to reduce slip and fall risks. Full article

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12 pages, 414 KiB

Open AccessArticle

Theoretical Estimates of the Critical Reynolds Number in the Flow around the Sphere on the Basis of Theory of Stochastic Equations and Equivalence of Measures

by Artur V. Dmitrenko and Vladislav M. Ovsyannikov

Fluids 2023, 8(3), 81; https://doi.org/10.3390/fluids8030081 - 23 Feb 2023

Viewed by 1235

Abstract

The aim of this investigation is to show the solution for the critical Reynolds number in the flow around the sphere on the basis of theory of stochastic equations and equivalence of measures between turbulent and laminar motions. Solutions obtained by numerical methods [...] Read more.

The aim of this investigation is to show the solution for the critical Reynolds number in the flow around the sphere on the basis of theory of stochastic equations and equivalence of measures between turbulent and laminar motions. Solutions obtained by numerical methods (DNS, LES, RANS) require verification and in this case the theoretical results have special value. For today in the scientific literature, there is J. Talor’s implicit formula connecting the critical Reynolds number with the parameters of the initial fluctuations in the flow around the sphere. Here the derivation of the explicit formula is presented. The results show a satisfactory correspondence of the obtained theoretical dependence for the critical Reynolds number to the experiments in the flow around the sphere. Full article

(This article belongs to the Collection Advances in Turbulence)

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16 pages, 1294 KiB

Open AccessArticle

Surrogate Models for Heat Transfer in Oscillating Flow with a Local Heat Source

by Simon Knecht, Denislav Zdravkov and Albert Albers

Fluids 2023, 8(3), 80; https://doi.org/10.3390/fluids8030080 - 22 Feb 2023

Cited by 1 | Viewed by 1121

Abstract

Simulative optimization methods often build on an iterative scheme, where a simulation model is solved in each iteration. To reduce the time needed for an optimization, finding the right balance between simulation model quality, and simulation time is essential. This is especially true [...] Read more.

Simulative optimization methods often build on an iterative scheme, where a simulation model is solved in each iteration. To reduce the time needed for an optimization, finding the right balance between simulation model quality, and simulation time is essential. This is especially true for transient problems, such as fluid flow within a hydromechanical system. Therefore, we present an approach to building steady-state surrogate models for oscillating flow in a pipe with a local heat source. The main aspect is to model the fluid as a solid with an orthotropic heat transfer coefficient. The values of this coefficient are fitted to reproduce the temperature distribution of the transient case by parametric optimization. It is shown that the presented approach is feasible for different sets of parameters and creates suitable surrogate models for oscillating flow within a pipe with a local heat source. In future works, the presented approach will be transferred from the simplified geometry under investigation to industrial problems. Full article

(This article belongs to the Special Issue Industrial CFD and Fluid Modelling in Engineering)

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11 pages, 1258 KiB

Open AccessArticle

Time-Dependent Numerical Modelling of Acoustic Cavitation in Liquid Metal Driven by Electromagnetic Induction

by Georgi Djambazov

Fluids 2023, 8(3), 79; https://doi.org/10.3390/fluids8030079 - 22 Feb 2023

Viewed by 833

Abstract

The numerically simulated method of using electromagnetic field from an alternating current is a patented method to create in liquid metal, under the conditions of resonance, acoustic waves of sufficient strength to cause cavitation and implosion of gas bubbles, leading to beneficial degassing [...] Read more.

The numerically simulated method of using electromagnetic field from an alternating current is a patented method to create in liquid metal, under the conditions of resonance, acoustic waves of sufficient strength to cause cavitation and implosion of gas bubbles, leading to beneficial degassing and grain refinement. The modelling stages of electromagnetics are described below along with acoustics in liquids, bubble dynamics, and their interactions. Sample results are presented for a cylindrical container with liquid aluminium surrounded by an induction coil. The possibility of establishing acoustic resonance and sustaining the bubble oscillation at a useful level is demonstrated. Limitations of the time-dependent approach to this multi-physics modelling problem are also discussed. Full article

(This article belongs to the Special Issue Numerical Simulations of Nonlinear Waves)

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27 pages, 11157 KiB

Open AccessArticle

Influence of Morphological Parameters on the Flow Development within Human Airways

by Andres Santiago Espinosa-Moreno, Carlos Alberto Duque-Daza and Diego Alexander Garzón-Alvarado

Fluids 2023, 8(3), 78; https://doi.org/10.3390/fluids8030078 - 21 Feb 2023

Viewed by 1488

Abstract

Anatomical airways parameters, such as length, diameter and angles, have a strong effect on the flow dynamics. Aiming to explore the effect of variations of the bifurcation angle (BA) and carina rounding radius (CRR) of lower human airways on respiratory processes, numerical simulations [...] Read more.

Anatomical airways parameters, such as length, diameter and angles, have a strong effect on the flow dynamics. Aiming to explore the effect of variations of the bifurcation angle (BA) and carina rounding radius (CRR) of lower human airways on respiratory processes, numerical simulations of airflow during inhalation and exhalation were performed using synthetic bifurcation models. Geometries for the airways models were parameterized based on a set of different BA’s and several CRR’s. A range of Reynolds numbers (Re), relevant to the human breathing process, were selected to analyze airflow behavior. The numerical results showed a significant influence of BA and the CRR on the development of the airflow within the airways, and, therefore, affecting the following relevant features of the flow: the deformation of velocity profiles, alterations of pressure drop, flow patterns, and, finally, enhancement or attenuation of wall shear stresses (WSS) appearing during the regular respiratory process. The numerical results showed that increases in the bifurcation angle value were accompanied by pressure increases of about 20%, especially in the regions close to the bifurcation. Similarly, increases in the BA value led to a reduction in peak shear stresses of up to 70%. For the ranges of angles and radii explored, an increase in pressure of about 20% and a reduction in wall shear stress of more than 400% were obtained by increasing the carina rounding radius. Analysis of the coherent structures and secondary flow patterns also revealed a direct relationship between the location of the vortical structures, the local maxima of the velocity profiles and the local vorticity minima. This relationship was observed for all branches analyzed, for both the inhalation and exhalation processes of the respiratory cycle. Full article

(This article belongs to the Special Issue Biological Fluid Dynamics)

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