Journal Description
Fluids
Fluids
is an international, peer-reviewed, open access journal on all aspects of fluids, published monthly online by MDPI. The Portuguese Society of Rheology (SPR) is affiliated with Fluids and its members receive discounts on the article processing charges.
- Open Access— free for readers, with article processing charges (APC) paid by authors or their institutions.
- High Visibility: indexed within Scopus, ESCI (Web of Science), Inspec, CAPlus / SciFinder, and other databases.
- Journal Rank: CiteScore - Q2 (Mechanical Engineering)
- Rapid Publication: manuscripts are peer-reviewed and a first decision is provided to authors approximately 20.7 days after submission; acceptance to publication is undertaken in 3.6 days (median values for papers published in this journal in the second half of 2023).
- Recognition of Reviewers: reviewers who provide timely, thorough peer-review reports receive vouchers entitling them to a discount on the APC of their next publication in any MDPI journal, in appreciation of the work done.
Impact Factor:
1.9 (2022);
5-Year Impact Factor:
1.8 (2022)
Latest Articles
Laminar Boundary Layer over a Serrated Backward-Facing Step
Fluids 2024, 9(6), 135; https://doi.org/10.3390/fluids9060135 (registering DOI) - 2 Jun 2024
Abstract
Laminar flow over a modified backward-facing step (BFS) was studied experimentally and computationally, with the results compared to a flight test on a Piper Cherokee wing. The BFS was modified with a serrated spanwise variation while maintaining a constant step height, and this
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Laminar flow over a modified backward-facing step (BFS) was studied experimentally and computationally, with the results compared to a flight test on a Piper Cherokee wing. The BFS was modified with a serrated spanwise variation while maintaining a constant step height, and this modification is termed a serrated BFS (sBFS). A scaling law was proposed and then used to develop the experimental operation conditions. The experiments showed evidence that the transition to turbulence was delayed over the forward part of the serration (termed the valley). The boundary layer growth and characterization were used to validate the computational model, which was then used to examine details not available from the experiment, including the wall shear stress distribution and streamlines as they go over the sBFS. The wall shear stress showed the formation of low-shear diamonds downstream of the sBFS valley that were associated with laminar flow, which confirmed previous assumptions about the low-shear diamonds observed in the flight tests. The length of the low-shear diamonds was scaled with the sBFS geometry. Finally, the streamlines showed that the near-wall flow forward of the sBFS is pumped towards the sBFS peak, where it rapidly transitions to turbulence at that location.
Full article
(This article belongs to the Special Issue Fluid Manipulation Techniques: Advances, Challenges and Perspectives)
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Open AccessArticle
AI-Based Detection of Surge and Rotating Stall in Axial Compressors via Dynamic Model Parameter Estimation
by
Sara Zanotti, Davide Ceschini and Michele Ferlauto
Fluids 2024, 9(6), 134; https://doi.org/10.3390/fluids9060134 (registering DOI) - 1 Jun 2024
Abstract
Compressors are an essential component of aircraft engines. Their design and operation must be extremely reliable as engine safety and performance depend greatly on these elements. Axial compressors exhibit instabilities, such as surge or rotating stall, in a region close to the peak
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Compressors are an essential component of aircraft engines. Their design and operation must be extremely reliable as engine safety and performance depend greatly on these elements. Axial compressors exhibit instabilities, such as surge or rotating stall, in a region close to the peak of their performance curves. These fluid dynamic instabilities can cause drops in efficiency, stress on the blades, fatigue, and even failures. Compressors are handled therefore by operating with a safety margin far from the surge line. Moreover, models able to predict onset instabilities and to reproduce them are of great interest. A dynamic system able to describe successfully both surge and rotating stall is the model presented by Moore and Greitzer That model has also been used for developing control laws of the compressor dynamics. The present work aims at developing an artificial neural network (ANN) approach able to predict either the permanence of the system in stable working condition or the onset instabilities from a time sequence of the compressor dynamics. Different solutions were tried to find the most suitable model for identifying the system, as well as the effects of the duration of the time sequence on the accuracy of the predicted compressor working conditions. The network was further tried for sequences with different initial values in order to perform a system analysis that included multiple variations from the initial database. The results show how it is possible to identify with high accuracy both rotating stall and surge with the ANN approach. Moreover, the presence of an underlying fluid dynamic model shares some similarities with physically informed AI procedures.
Full article
(This article belongs to the Special Issue Flow Control Techniques: Advances in Flow System Analysis, Modeling and Applications)
Open AccessReview
Convergence towards High-Speed Steady States Using High-Order Accurate Shock-Capturing Schemes
by
Juan C. Assis, Ricardo D. Santos, Mateus S. Schuabb, Carlos E. G. Falcão, Rômulo B. Freitas and Leonardo S. de B. Alves
Fluids 2024, 9(6), 133; https://doi.org/10.3390/fluids9060133 (registering DOI) - 1 Jun 2024
Abstract
Creating time-marching unsteady governing equations for a steady state in high-speed flows is not a trivial task. Residue convergence in time cannot be achieved when using most low- and high-order spatial discretization schemes. Recently, high-order, weighted, essentially non-oscillatory schemes have been specially designed
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Creating time-marching unsteady governing equations for a steady state in high-speed flows is not a trivial task. Residue convergence in time cannot be achieved when using most low- and high-order spatial discretization schemes. Recently, high-order, weighted, essentially non-oscillatory schemes have been specially designed for steady-state simulations. They have been shown to be capable of achieving machine precision residues when simulating the Euler equations under canonical coordinates. In the present work, we review these schemes and show that they can also achieve machine residues when simulating the Navier–Stokes equations under generalized coordinates. This is carried out by considering three supersonic flows of perfect fluids, namely the flow upstream a cylinder, the flow over a blunt wedge, and the flow over a compression ramp.
Full article
(This article belongs to the Special Issue Recent Advances in Fluid Mechanics: Feature Papers, 2024)
Open AccessArticle
Gas–Liquid Mass Transfer Intensification for Selective Alkyne Semi-Hydrogenation with an Advanced Elastic Catalytic Foam-Bed Reactor
by
Mohamad Fayad, Maïté Michaud, Han Peng, Vincent Ritleng and David Edouard
Fluids 2024, 9(6), 132; https://doi.org/10.3390/fluids9060132 (registering DOI) - 1 Jun 2024
Abstract
The Elastic Catalytic Foam-bed Reactor (EcFR) technology was used to enhance a model catalytic hydrogenation reaction by improving gas–liquid mass transfer. This advanced technology is based on a column packed with a commercial elastomeric polyurethane open-cell foam, which also acts as a catalyst
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The Elastic Catalytic Foam-bed Reactor (EcFR) technology was used to enhance a model catalytic hydrogenation reaction by improving gas–liquid mass transfer. This advanced technology is based on a column packed with a commercial elastomeric polyurethane open-cell foam, which also acts as a catalyst support. A simple and efficient crankshaft-inspired system applied in situ compression/relaxation movements to the foam bed. For the first time, the catalytic support parameters (i.e., porosity, tortuosity, characteristic length, etc.) underwent cyclic and controlled changes over time. These dynamic cycles have made it possible to intensify the transfer of gas to liquid at a constant energy level. The application chosen was the selective hydrogenation of phenylacetylene to styrene in an alcoholic solution using a palladium-based catalyst under hydrogen bubble conditions. The conversion observed with this EcFR at 1 Hz as cycle frequency was compared with that observed with a conventional Fixed Catalytic Foam-bed Reactor (FcFR).
Full article
(This article belongs to the Special Issue Mass Transfer in Multiphase Reactors)
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Open AccessArticle
Passive Control of Vortices in the Wake of a Bluff Body
by
Marek Pátý, Michael Valášek, Emanuele Resta, Roberto Marsilio and Michele Ferlauto
Fluids 2024, 9(6), 131; https://doi.org/10.3390/fluids9060131 - 31 May 2024
Abstract
Vortices belong to the most important phenomena in fluid dynamics and play an essential role in many engineering applications. They can act detrimentally by harnessing the flow energy and reducing the efficiency of an aerodynamic device, whereas in other cases, their presence can
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Vortices belong to the most important phenomena in fluid dynamics and play an essential role in many engineering applications. They can act detrimentally by harnessing the flow energy and reducing the efficiency of an aerodynamic device, whereas in other cases, their presence can be exploited to achieve targeted flow conditions. The control of the vortex parameters is desirable in both cases. In this paper, we introduce an optimization strategy for the control of vortices in the wake of a bluff body. Flow modelling is based on RANS and DES computations, validated by experimental data. The algorithm for vortex identification and characterization is based on the triple decomposition of motion. It produces a quantitative measure of vortex strength which is used to define the objective function in the optimization procedure. It is shown how the shape of an aerodynamic device can be altered to achieve the desired characteristics of vortices in its wake. The studied case is closely related to flame holders for combustion applications, but the conceptual approach has a general applicability to vortex control.
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Open AccessArticle
Improving the Energy Efficiency of Vehicles by Ensuring the Optimal Value of Excess Pressure in the Cabin Depending on the Travel Speed
by
Ivan Panfilov, Alexey N. Beskopylny and Besarion Meskhi
Fluids 2024, 9(6), 130; https://doi.org/10.3390/fluids9060130 - 31 May 2024
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This work is devoted to the study of gas-dynamic processes in the operation of climate control systems in the cabins of vehicles (HVAC), focusing on pressure values. This research examines the issue of assessing the required values of air overpressure inside the locomotive
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This work is devoted to the study of gas-dynamic processes in the operation of climate control systems in the cabins of vehicles (HVAC), focusing on pressure values. This research examines the issue of assessing the required values of air overpressure inside the locomotive cabin, which is necessary to prevent gas exchange between the interior of the cabin and the outside air through leaks in the cabin, including protection against the penetration of harmful substances. The pressure boost in the cabin depends, among other things, on the external air pressure on the locomotive body, the power of the climate system fan, and the ratio of the input and output deflectors. To determine the external air pressure, the problem of train movement in a wind tunnel is considered, the internal and external fluids domain is considered, and the air pressure on the cabin skin is determined using numerical methods CFD based on the Navier–Stokes equations, depending on the speed of movement. The finite-volume modeling package Ansys CFD (Fluent) was used as an implementation. The values of excess internal pressure, which ensures the operation of the climate system under different operating modes, were studied numerically and on the basis of an approximate applied formula. In particular, studies were carried out depending on the speed and movement of transport, on the airflow of the climate system, and on the ratio of the areas of input and output parameters. During a numerical experiment, it was found that for a train speed of 100 km/h, the required excess pressure is 560 kPa, and the most energy-efficient way to increase pressure is to regulate the area of the outlet valves.
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Open AccessArticle
Hartmann Flow of Two-Layered Fluids in Horizontal and Inclined Channels
by
Arseniy Parfenov, Alexander Gelfgat, Amos Ullmann and Neima Brauner
Fluids 2024, 9(6), 129; https://doi.org/10.3390/fluids9060129 - 30 May 2024
Abstract
The effect of a transverse magnetic field on two-phase stratified flow in horizontal and inclined channels is studied. The lower heavier phase is assumed to be an electrical conductor (e.g., liquid metal), while the upper lighter phase is fully dielectric (e.g., gas). The
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The effect of a transverse magnetic field on two-phase stratified flow in horizontal and inclined channels is studied. The lower heavier phase is assumed to be an electrical conductor (e.g., liquid metal), while the upper lighter phase is fully dielectric (e.g., gas). The flow is defined by prescribed flow rates in each phase, so the unknown frictional pressure gradient and location of the interface separating the phases (holdup) are found as part of the whole solution. It is shown that the solution of such a two-phase Hartmann flow is determined by four dimensionless parameters: the phases’ viscosity and flow-rate ratios, the inclination parameter, and the Hartmann number. The changes in velocity profiles, holdups, and pressure gradients with variations in the magnetic field and the phases’ flow-rate ratio are reported. The potential lubrication effect of the gas layer and pumping power reduction are found to be limited to low magnetic field strength. The effect of the magnetic field strength on the possibility of obtaining countercurrent flow and multiple flow states in concurrent upward and downward flows, and the associated flow characteristics, such as velocity profiles, back-flow phenomena, and pressure gradient, are explored. It is shown that increasing the magnetic field strength reduces the flow-rate range for which multiple solutions are obtained in concurrent flows and the flow-rate range where countercurrent flow is feasible.
Full article
(This article belongs to the Special Issue Numerical Modeling and Experimental Studies of Two-Phase Flows)
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Open AccessArticle
Measuring Turbulent Flows: Analyzing a Stochastic Process with Stochastic Tools
by
Evangelos Rozos, Jörg Wieland and Jorge Leandro
Fluids 2024, 9(6), 128; https://doi.org/10.3390/fluids9060128 - 30 May 2024
Abstract
Assessing drag force and Reynolds stresses in turbulent flows is crucial for evaluating the stability and longevity of hydraulic structures. Yet, this task is challenging due to the complex nature of turbulent flows. To address this, physical models are often employed. Nonetheless, this
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Assessing drag force and Reynolds stresses in turbulent flows is crucial for evaluating the stability and longevity of hydraulic structures. Yet, this task is challenging due to the complex nature of turbulent flows. To address this, physical models are often employed. Nonetheless, this practice is associated with difficulties, especially in the case of high sampling frequency where the inherent randomness of velocity fluctuations becomes mixed with the measurement noise. This study introduces a stochastic approach, which aims to mitigate bias from measurement errors and provide a probabilistic estimate of extreme stress values. To accomplish this, a simple experimental setup with a hydraulic jump was employed to acquire long-duration velocity measurements. Subsequently, a modified first-order autoregressive model was applied through ensemble simulations, demonstrating the benefits of the stochastic approach. The analysis highlights its effectiveness in estimating the uncertainty of extreme events frequency and minimizing the bias induced by the noise in the high-magnitude velocity measurements and by the limited length of observations. These findings contribute to advancing our understanding of turbulent flow analysis and have implications for the design and assessment of hydraulic structures.
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(This article belongs to the Collection Advances in Turbulence)
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Open AccessFeature PaperReview
Numerical Dissipation Control in High-Order Methods for Compressible Turbulence: Recent Development
by
H. C. Yee and Björn Sjögreen
Fluids 2024, 9(6), 127; https://doi.org/10.3390/fluids9060127 - 29 May 2024
Abstract
This comprehensive overview presents our continued efforts in high-order finite difference method (FDM) development for adaptive numerical dissipation control in the long-time integration of direct numerical simulation (DNS), large eddy simulation (LES), and implicit LES (ILES) computations of compressible turbulence for gas dynamics
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This comprehensive overview presents our continued efforts in high-order finite difference method (FDM) development for adaptive numerical dissipation control in the long-time integration of direct numerical simulation (DNS), large eddy simulation (LES), and implicit LES (ILES) computations of compressible turbulence for gas dynamics and MHD. The focus is on turbulence with shock wave numerical simulations using the adaptive blending of high-order structure-preserving non-dissipative methods (classical central, Padé (compact), and dispersion relation-preserving (DRP)) with high-order shock-capturing methods in such a way that high-order shock-capturing methods are active only in the vicinity of shock/shear waves, and high-gradient and spurious high-frequency oscillation regions guided via flow sensors. Any efficient and high-resolution high-order shock-capturing methods are good candidates for the blending of methods procedure. Typically, the adaptive blending of more than one method falls under two camps: hybrid methods and nonlinear filter methods. They are applicable to unstructured finite volume, finite element, discontinuous Galerkin, and spectral element methods. This work represents the culmination of over 20 years of high-order FDM developments and hands-on experience by the authors and collaborators in adaptive numerical dissipation control using the “high order nonlinear filter approach”. Extensions of these FDM versions to curvilinear nonuniform, freestream-preserving moving grids and time-varying deforming grids were also developed. By examining the construction of these two approaches using the high-order multistage type of temporal discretization, the nonlinear filter approach is made more efficient and less CPU-intensive while obtaining similar accuracy. A representative variety of test cases that compare the various blending of high-order methods with standalone standard methods is illustrated. Due to the fact that our nonlinear filter methods are not well known in compressible turbulence with shock waves, the intent of this comprehensive overview is for general audiences who are not familiar with our nonlinear filter methods. For readers interested in the implementation of our methods into their computer code, it is hoped that the long overview will be helpful.
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(This article belongs to the Special Issue Next-Generation Methods for Turbulent Flows)
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Open AccessArticle
Statistical Analysis of Bubble Parameters from a Model Bubble Column with and without Counter-Current Flow
by
P. Kováts and K. Zähringer
Fluids 2024, 9(6), 126; https://doi.org/10.3390/fluids9060126 - 28 May 2024
Abstract
Bubble columns are widely used in numerous industrial processes because of their advantages in operation, design, and maintenance compared to other multiphase reactor types. In contrast to their simple design, the generated flow conditions inside a bubble column reactor are quite complex, especially
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Bubble columns are widely used in numerous industrial processes because of their advantages in operation, design, and maintenance compared to other multiphase reactor types. In contrast to their simple design, the generated flow conditions inside a bubble column reactor are quite complex, especially in continuous mode with counter-current liquid flow. For the design and optimization of such reactors, precise numerical simulations and modelling are needed. These simulations and models have to be validated with experimental data. For this reason, experiments were carried out in a laboratory-scale bubble column using shadow imaging and particle image velocimetry (PIV) techniques with and without counter-current liquid flow. In the experiments, two types of gases—relatively poorly soluble air and well-soluble CO2—were used and the bubbles were generated with three different capillary diameters. With changing gas and liquid flow rates, overall, 108 different flow conditions were investigated. In addition to the liquid flow fields captured by PIV, shadow imaging data were also statistically evaluated in the measurement volume and bubble parameters such as bubble diameter, velocity, aspect ratio, bubble motion direction, and inclination. The bubble slip velocity was calculated from the measured liquid and bubble velocities. The analysis of these parameters shows that the counter-current liquid flow has a noticeable influence on the bubble parameters, especially on the bubble velocity and motion direction. In the case of CO2 bubbles, remarkable bubble shrinkage was observed with counter-current liquid flow due to the enhanced mass transfer. The results obtained for bubble aspect ratio are compared to known correlations from the literature. The comprehensive and extensive bubble data obtained in this study will now be used as a source for the development of correlations needed in the validation of numerical simulations and models. The data are available from the authors on request.
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(This article belongs to the Special Issue Mass Transfer in Multiphase Reactors)
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Open AccessArticle
Effects of Partial Premixing and Coflow Temperature on Flame Stabilization of Lifted Jet Flames of Dimethyl Ether in a Vitiated Coflow Based on Stochastic Multiple Mapping Conditioning Approach
by
Sanjeev Kumar Ghai, Rajat Gupta and Santanu De
Fluids 2024, 9(6), 125; https://doi.org/10.3390/fluids9060125 - 26 May 2024
Abstract
The Reynolds-averaged Navier–Stokes (RANS)-based stochastic multiple mapping conditioning (MMC) approach has been used to study partially premixed jet flames of dimethyl ether (DME) introduced into a vitiated coflowing oxidizer stream. This study investigates DME flames with varying degrees of partial premixing within a
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The Reynolds-averaged Navier–Stokes (RANS)-based stochastic multiple mapping conditioning (MMC) approach has been used to study partially premixed jet flames of dimethyl ether (DME) introduced into a vitiated coflowing oxidizer stream. This study investigates DME flames with varying degrees of partial premixing within a fuel jet across different coflow temperatures, delving into the underlying flame structure and stabilization mechanisms. Employing a turbulence k- model with a customized set of constants, the MMC technique utilizes a mixture fraction as the primary scalar, mapped to the reference variable. Solving a set of ordinary differential equations for the evolution of Lagrangian stochastic particles’ position and composition, the molecular mixing of these particles is executed using the modified Curl’s model. The lift-off height (LOH) derived from RANS-MMC simulations are juxtaposed with experimental data for different degrees of partial premixing of fuel jets and various coflow temperatures. The RANS-MMC methodology adeptly captures LOH for pure DME jets but exhibits an underestimation of flame LOH for partially premixed jet scenarios. Notably, as the degree of premixing escalates, a conspicuous underprediction in LOH becomes apparent. Conditional scatter and contour plots of OH and CH2O unveil that the propagation of partially premixed flames emerges as the dominant mechanism at high coflow temperatures, while autoignition governs flame stabilization at lower coflow temperatures in partially premixed flames. Additionally, for pure DME flames, autoignition remains the primary flame stabilization mechanism across all coflow temperature conditions. The study underscores the importance of considering the degree of premixing in partially premixed jet flames, as it significantly impacts flame stabilization mechanisms and LOH, thereby providing crucial insights into combustion dynamics for various practical applications.
Full article
(This article belongs to the Special Issue Future Trends and Challenges in High Performance Computing for Turbulence)
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Open AccessArticle
Subgrid Turbulent Flux Models for Large Eddy Simulations of Diffusion Flames in Space Propulsion
by
Daniel Martinez-Sanchis, Andrej Sternin, Sagnik Banik, Oskar Haidn and Martin Tajmar
Fluids 2024, 9(6), 124; https://doi.org/10.3390/fluids9060124 - 26 May 2024
Abstract
Subgrid scale models for unresolved turbulent fluxes are investigated, with a focus on combustion for space propulsion applications. An extension to the gradient model is proposed, introducing a dependency on the local burning regimen. The dynamic behaviors of the model’s coefficients are investigated,
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Subgrid scale models for unresolved turbulent fluxes are investigated, with a focus on combustion for space propulsion applications. An extension to the gradient model is proposed, introducing a dependency on the local burning regimen. The dynamic behaviors of the model’s coefficients are investigated, and scaling laws are studied. The discussed models are validated using a DNS database of a high-pressure, turbulent, fuel-rich methane–oxygen diffusion flame. The operating point and turbulence characteristics are selected to resemble those of modern combustors for space propulsion applications to support the future usage of the devised model in this context.
Full article
(This article belongs to the Special Issue Turbulence and Combustion)
Open AccessArticle
Simulation on the Separation of Breast Cancer Cells within a Dual-Patterned End Microfluidic Device
by
Diganta Dutta, Xavier Palmer, Jung Yul Lim and Surabhi Chandra
Fluids 2024, 9(6), 123; https://doi.org/10.3390/fluids9060123 - 25 May 2024
Abstract
Microfluidic devices have long been useful for both the modeling and diagnostics of numerous diseases. In the past 20 years, they have been increasingly adopted for helping to study those in the family of breast cancer through characterizing breast cancer cells and advancing
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Microfluidic devices have long been useful for both the modeling and diagnostics of numerous diseases. In the past 20 years, they have been increasingly adopted for helping to study those in the family of breast cancer through characterizing breast cancer cells and advancing treatment research in portable and replicable formats. This paper adds to the body of work concerning cancer-focused microfluidics by proposing a simulation of a hypothetical bi-ended three-pronged device with a single channel and 16 electrodes with 8 pairs under different voltage and frequency regimes using COMSOL. Further, a study was conducted to examine the frequencies most effective for ACEO to separate cancer cells and accompanying particles. The study revealed that the frequency of EF has a more significant impact on the separation of particles than the inlet velocity. Inlet velocity variations while holding the frequency of EF constant resulted in a consistent trend showing a direct proportionality between inlet velocity and net velocity. These findings suggest that optimizing the frequency of EF could lead to more effective particle separation and targeted therapeutic interventions for breast cancer. This study hopefully will help to create targeted therapeutic interventions by bridging the disparity between in vitro and in vivo models.
Full article
(This article belongs to the Special Issue Physics and Applications of Microfluidics)
Open AccessArticle
N-Symmetric Interaction of N Hetons, II: Analysis of the Case of Arbitrary N
by
Konstantin V. Koshel, Mikhail A. Sokolovskiy, David G. Dritschel and Jean N. Reinaud
Fluids 2024, 9(6), 122; https://doi.org/10.3390/fluids9060122 - 24 May 2024
Abstract
This paper seeks and examines N-symmetric vortical solutions of the two-layer geostrophic model for the special case when the vortices (or eddies) have vanishing summed strength (circulation anomaly). This study is an extension [Sokolovskiy et al. Phys. Fluids 2020, 32, 09660], where
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This paper seeks and examines N-symmetric vortical solutions of the two-layer geostrophic model for the special case when the vortices (or eddies) have vanishing summed strength (circulation anomaly). This study is an extension [Sokolovskiy et al. Phys. Fluids 2020, 32, 09660], where the general formulation for arbitrary N was given, but the analysis was only carried out for . Here, families of stationary solutions are obtained and their properties, including asymptotic ones, are investigated in detail. From the point of view of geophysical applications, the results may help interpret the propagation of thermal anomalies in the oceans.
Full article
(This article belongs to the Collection Advances in Geophysical Fluid Dynamics)
Open AccessArticle
Novel Pour Point Depressants for Crude Oil Derived from Polyethylene Solution in Hexane and Coal Fly Ash
by
Kazim Nadirov, Manap Zhantasov, Tlek Ketegenov, Zhanna Nadirova, Aisulu Batkal, Kaster Kamunur, Gulmira Bimbetova and Rashid Nadirov
Fluids 2024, 9(6), 121; https://doi.org/10.3390/fluids9060121 - 23 May 2024
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Oil transportation becomes much more complicated due to the solidification of paraffins in them at low temperatures and the resulting increase in oil viscosity. To solve this problem, special additives as pour point depressants (PPDs) are used to prevent the agglomeration of paraffin
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Oil transportation becomes much more complicated due to the solidification of paraffins in them at low temperatures and the resulting increase in oil viscosity. To solve this problem, special additives as pour point depressants (PPDs) are used to prevent the agglomeration of paraffin crystals. In this work, 15 PPDs were obtained and tested, consisting of a solution of polyethylene in hexane and also, in some cases, from magnetic nanoparticles (MNPs) extracted from coal fly ash. The most effective result was observed with a mixture of 0.25% polyethylene in hexane and 2% MNPs, which managed to lower the oil’s pour point from 18 °C to −17 °C.
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Open AccessEditorial
Environmental Hydraulics, Turbulence, and Sediment Transport, Second Edition
by
Jaan H. Pu, Manish Pandey and Prashanth Reddy Hanmaiahgari
Fluids 2024, 9(6), 120; https://doi.org/10.3390/fluids9060120 - 22 May 2024
Abstract
Within river systems, the process of bed-forming is intricate, dynamic and is shaped by different factors [...]
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(This article belongs to the Special Issue Environmental Hydraulics, Turbulence and Sediment Transport, 2nd edition)
Open AccessArticle
Circular Fluid Heating—Transient Entropy Generation
by
Fikret Alic
Fluids 2024, 9(5), 119; https://doi.org/10.3390/fluids9050119 - 18 May 2024
Abstract
A technical issue with fluid flow heating is the relatively small temperature increase as the fluid passes through the heating surface. The fluid does not spend enough time inside the heating source to significantly raise its temperature, despite the heating source itself experiencing
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A technical issue with fluid flow heating is the relatively small temperature increase as the fluid passes through the heating surface. The fluid does not spend enough time inside the heating source to significantly raise its temperature, despite the heating source itself experiencing a substantial increase. To address this challenge, the concept of the multiple circular heating of air was developed, forming the basis of this work. Two PTC heaters with longitudinal fins are located within a closed channel inside housing composed of a thermal insulation material. Air flows circularly from one finned surface to another. Analytical modeling and experimental testing were used in the analysis, with established restrictions and boundary conditions. An important outcome of the analysis was the methodology established for the optimization of the geometric and process parameters based on minimizing the transient thermal entropy. In conducting the analytical modeling, the temperature of the PTC heater was assumed to be constant at 150 °C and 200 °C. By removing the restrictions and adjusting the boundary conditions, the established methodology for the analysis and optimization of various thermally transient industrial processes can be applied more widely. The experimental determination of the transient thermal entropy was performed at a much higher air flow rate of 0.005 m3s−1 inside the closed channel. The minimum transient entropy also indicates the optimal time for the opening of the channel, allowing the heated air to exit. The novelty of this work lies in the controlled circular heating of the fluid and the establishment of the minimum transient thermal entropy as an optimization criterion.
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(This article belongs to the Special Issue Evaporation, Condensation and Heat Transfer)
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Open AccessArticle
A Variational Surface-Evolution Approach to Optimal Transport over Transitioning Compact Supports with Domain Constraints
by
Anthony Yezzi
Fluids 2024, 9(5), 118; https://doi.org/10.3390/fluids9050118 - 16 May 2024
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We examine the optimal mass transport problem in between densities with transitioning compact support by considering the geometry of a continuous interpolating support boundary in space-time within which the mass density evolves according to the fluid dynamical framework of Benamou
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We examine the optimal mass transport problem in between densities with transitioning compact support by considering the geometry of a continuous interpolating support boundary in space-time within which the mass density evolves according to the fluid dynamical framework of Benamou and Brenier. We treat the geometry of this space-time embedding in terms of points, vectors, and sets in and blend the mass density and velocity as well into a space-time solenoidal vector field over a compact set . We then formulate a joint optimization for and its support using the shaped gradient of the space-time surface outlining the support boundary . This easily accommodates spatiotemporal constraints, including obstacles or mandatory regions to visit.
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Open AccessArticle
Physical and Numerical Experimentation of Water Droplet Collision on a Wall: A Comparison between PLIC and HRIC Schemes for the VOF Transport Equation with High-Speed Imaging
by
Bruno Silva de Lima, Martin Sommerfeld and Francisco José de Souza
Fluids 2024, 9(5), 117; https://doi.org/10.3390/fluids9050117 - 16 May 2024
Abstract
Liquid films are often found in engineering applications with thicknesses ranging from micrometer scales to large scales with a wide range of applications. To optimize such systems, researchers have dedicated themselves to the development of new techniques. To further contribute to this development,
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Liquid films are often found in engineering applications with thicknesses ranging from micrometer scales to large scales with a wide range of applications. To optimize such systems, researchers have dedicated themselves to the development of new techniques. To further contribute to this development, the objective of this work is to present the results of the collision of water droplets on a wall by means of experimentation and numerical simulations. For physical experimentation, an injector is used to generate a chain of water droplets that collide with the opposite wall, forming a liquid film. Images of the droplets were obtained using two high-speed recording cameras. The results for different droplet sizes and impact angles are presented and the relationship between the momentum parameter and non-dimensional pool size was established. Modeling such processes is a common challenge in engineering, with different techniques having their advantages and limitations. The simulations in this work were run using the volume of fluid method, which consists of solving a transport equation for the volume fraction of each considered fluid. A correlation was found between the surface tension to momentum transport ratio, Scd, and the non-dimensional pool size for different droplet sizes and impact angles. Regions where partial depositions were most likely to occur were found via physical experiments.
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(This article belongs to the Special Issue Multiphase Flow and Granular Mechanics)
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Open AccessArticle
Turbulence and Rossby Wave Dynamics with Realizable Eddy Damped Markovian Anisotropic Closure
by
Jorgen S. Frederiksen and Terence J. O’Kane
Fluids 2024, 9(5), 116; https://doi.org/10.3390/fluids9050116 - 16 May 2024
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The theoretical basis for the Eddy Damped Markovian Anisotropic Closure (EDMAC) is formulated for two-dimensional anisotropic turbulence interacting with Rossby waves in the presence of advection by a large-scale mean flow. The EDMAC is as computationally efficient as the Eddy Damped Quasi Normal
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The theoretical basis for the Eddy Damped Markovian Anisotropic Closure (EDMAC) is formulated for two-dimensional anisotropic turbulence interacting with Rossby waves in the presence of advection by a large-scale mean flow. The EDMAC is as computationally efficient as the Eddy Damped Quasi Normal Markovian (EDQNM) closure, but, in contrast, is realizable in the presence of transient waves. The EDMAC is arrived at through systematic simplification of a generalization of the non-Markovian Direct Interaction Approximation (DIA) closure that has its origin in renormalized perturbation theory. Markovian Anisotropic Closures (MACs) are obtained from the DIA by using three variants of the Fluctuation Dissipation Theorem (FDT) with the information in the time history integrals instead carried by Markovian differential equations for two relaxation functions. One of the MACs is simplified to the EDMAC with analytical relaxation functions and high numerical efficiency, like te EDQNM. Sufficient conditions for the EDMAC to be realizable in the presence of Rossby waves are determined. Examples of the numerical integration of the EDMAC compared with the EDQNM are presented for two-dimensional isotropic and anisotropic turbulence, at moderate Reynolds numbers, possibly interacting with Rossby waves and large-scale mean flow. The generalization of the EDMAC for the statistical dynamics of other physical systems to higher dimension and higher order nonlinearity is considered.
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