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
A New Non-Extensive Equation of State for the Fluid Phases of Argon, Including the Metastable States, from the Melting Line to 2300 K and 50 GPa
Fluids 2024, 9(5), 102; https://doi.org/10.3390/fluids9050102 - 24 Apr 2024
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A new equation of state for argon was developed with the view of extending the range of validity of the equation of state previously proposed by Tegeler et al. and obtaining a better physical description of the experimental thermodynamic data for the whole
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A new equation of state for argon was developed with the view of extending the range of validity of the equation of state previously proposed by Tegeler et al. and obtaining a better physical description of the experimental thermodynamic data for the whole fluid region (single-phase, metastable, and saturation states). As proposed by Tegeler et al., this equation is also based on a functional form of the residual part of the reduced Helmholtz free energy. However, in this work, the fundamental equation for Helmholtz free energy was derived from the measured quantities CV(ρ, T) and P(ρ, T). The empirical description of the isochoric heat capacity CV(ρ, T) was based on an original empirical description explicitly containing the metastable states. The thermodynamic properties (internal energy, entropy, and free energy) were then obtained by combining the integration of CV(ρ, T). The arbitrary functions introduced by the integration process were deduced from a comparison between calculated and experimental pressure P(ρ, T) data. The new formulation is valid for the whole fluid region from the melting line to 2300 K and for pressures up to 50 GPa. It also predicts the existence of a maximum of the isochoric heat capacity CV along isochors, as experimentally observed in several other fluids. For many applications, an approximate form of the equation of state for the liquid phase may be sufficient. A Tait–Tammann equation is therefore proposed between the triple-point temperature and 148 K.
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Open AccessArticle
Understanding the Influence of the Buoyancy Sign on Buoyancy-Driven Particle Clouds
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Ali O. Alnahit, Nigel Berkeley Kaye and Abdul A. Khan
Fluids 2024, 9(5), 101; https://doi.org/10.3390/fluids9050101 - 23 Apr 2024
Abstract
A numerical model was developed to investigate the behavior of round buoyancy-driven particle clouds in a quiescent ambient. The model was validated by comparing model simulations with prior experimental and numerical results and then applied the model to examine the difference between releases
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A numerical model was developed to investigate the behavior of round buoyancy-driven particle clouds in a quiescent ambient. The model was validated by comparing model simulations with prior experimental and numerical results and then applied the model to examine the difference between releases of positively and negatively buoyant particles. The particle cloud model used the entrainment assumption while approximating the flow field induced by the cloud as a Hill’s spherical vortex. The motion of individual particles was resolved using a particle tracking equation that considered the forces acting on them and the induced velocity field. The simulation results showed that clouds with the same initial buoyancy magnitude and particle Reynolds number behaved differently depending on whether the particles were more dense or less dense than the ambient fluid. This was found even for very low initial buoyancy releases, suggesting that the sign of the buoyancy is always important and that, therefore, the Boussinesq assumption is never fully appropriate for such flows.
Full article
(This article belongs to the Special Issue Environmental Hydraulics, Turbulence and Sediment Transport, 2nd edition)
Open AccessArticle
Liquid-Solid Interaction to Evaluate Thermal Aging Effects on Carbon Fiber-Reinforced Composites
by
Poom Narongdej, Jack Hanson, Ehsan Barjasteh and Sara Moghtadernejad
Fluids 2024, 9(5), 100; https://doi.org/10.3390/fluids9050100 - 23 Apr 2024
Abstract
This study investigated the thermally induced aging effects on a carbon fiber-reinforced composite (CFRP) comprising benzoxazine (BZ) and cycloaliphatic epoxy resin (CER). Herein, we employed various testing methodologies to assess the aging behavior of CFRP samples with differing CER and BZ ratios. Traditional
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This study investigated the thermally induced aging effects on a carbon fiber-reinforced composite (CFRP) comprising benzoxazine (BZ) and cycloaliphatic epoxy resin (CER). Herein, we employed various testing methodologies to assess the aging behavior of CFRP samples with differing CER and BZ ratios. Traditional techniques, including weight change quantification and qualitative analysis of surface morphology, reveal that higher CER content correlates with increased aging. Additionally, wettability analysis demonstrates that both BZ and BZ-CER composites exhibit heightened hydrophilicity with thermal aging, potentially exacerbating concerns such as icing and surface erosion. Notably, the BZ-CER composite displays greater hydrophilicity compared to the BZ composite, consistent with weight change trends. These findings underscore the utility of surface wettability analysis as a valuable tool for monitoring thermo-oxidative aging in polymers and their surface behavior in response to fluid interactions, particularly within high glass transition temperature ( ) BZ-CER systems utilized in structural composite applications.
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(This article belongs to the Special Issue Advances in Multiphase Flow Science and Technology, 2nd Edition)
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A New Solution of Drag for Newtonian Fluid Droplets in a Power-Law Fluid
by
Jianting Zhu
Fluids 2024, 9(4), 99; https://doi.org/10.3390/fluids9040099 - 21 Apr 2024
Abstract
Understanding flow behaviors of multiple droplets in complex non-Newtonian fluids is crucial in many science and engineering applications. In this study, a new and improved analytical solution is developed based on the free surface cell model for the flow drag of swamp of
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Understanding flow behaviors of multiple droplets in complex non-Newtonian fluids is crucial in many science and engineering applications. In this study, a new and improved analytical solution is developed based on the free surface cell model for the flow drag of swamp of Newtonian fluid drops through a power-law fluid. The developed solution is accurate and compares well to the numerical solutions. The improvement involves a new quantification of shear stress boundary condition at the interface and a more consistent approximation in linearizing the power-law fluid flow governing equation. The Newtonian fluid solutions can be reasonably used to linearize the flow governing equation. The approximation of the boundary conditions at the interface, however, has a major impact on the model prediction. The main improvement in the new solution is observed under the condition of comparable viscosities of the Newtonian drops and the outside power-law fluid when the results are sensitive to the interface boundary condition. Under the two extreme conditions of high viscosity ratio (approaching particles) and low ratio (approaching bubbles), the present and existing solutions converge.
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(This article belongs to the Special Issue Non-Newtonian Flow: Interfacial and Bulk Phenomena)
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Open AccessCommunication
A Note on the Moody Diagram
by
Paulo R. de Souza Mendes
Fluids 2024, 9(4), 98; https://doi.org/10.3390/fluids9040098 - 21 Apr 2024
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In this work, we underscore the significance of selecting an appropriate scaling to derive dimensionless quantities that accurately reflect their dimensional counterparts, thereby enhancing the comprehension of the underlying physics. For the loss of head in a pipe flow, we argue that employing
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In this work, we underscore the significance of selecting an appropriate scaling to derive dimensionless quantities that accurately reflect their dimensional counterparts, thereby enhancing the comprehension of the underlying physics. For the loss of head in a pipe flow, we argue that employing inertial force (or kinetic energy) to non-dimensionalized pressure force (or mechanical energy loss) lacks physical justification. As a result, an anomalous trend emerges for the classical friction factor: it decreases as the dimensionless flow rate (Reynolds number) increases, contrary to the behavior observed in the corresponding dimensional quantities. Conversely, by non-dimensionalizing the pressure force with the viscous force, a novel friction factor arises. In laminar flow, it is constant, while in turbulent flow, it is a monotonically increasing function of the Reynolds number, mirroring the behavior observed in the dimensional problem.
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Open AccessArticle
Nonlinear Approach to Jouguet Detonation in Perpendicular Magnetic Fields
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Andriy A. Avramenko, Igor V. Shevchuk, Margarita M. Kovetskaya, Yulia Y. Kovetska and Andrii I. Tyrinov
Fluids 2024, 9(4), 97; https://doi.org/10.3390/fluids9040097 - 20 Apr 2024
Abstract
The focus of this paper was Jouguet detonation in an ideal gas flow in a magnetic field. A modified Hugoniot detonation equation has been obtained, taking into account the influence of the magnetic field on the detonation process and the parameters of the
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The focus of this paper was Jouguet detonation in an ideal gas flow in a magnetic field. A modified Hugoniot detonation equation has been obtained, taking into account the influence of the magnetic field on the detonation process and the parameters of the detonation wave. It was shown that, under the influence of a magnetic field, combustion products move away from the detonation front at supersonic speed. As the magnetic field strength increases, the speed of the detonation products also increases. A dependence has been obtained that allows us to evaluate the influence of heat release on detonation parameters.
Full article
(This article belongs to the Collection Challenges and Advances in Heat and Mass Transfer)
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Open AccessArticle
Analysis of MAV Rotors Optimized for Low Noise and Aerodynamic Efficiency with Operational Constraints
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Pietro Li Volsi, Gianluigi Brogna, Romain Gojon, Thierry Jardin, Hélène Parisot-Dupuis and Jean-Marc Moschetta
Fluids 2024, 9(4), 96; https://doi.org/10.3390/fluids9040096 - 19 Apr 2024
Abstract
The rapid growth of drone use in urban areas has prompted authorities to review airspace regulations, forcing drone manufacturers to anticipate and reduce the noise emissions during the design stage. Additionally, micro air vehicles (MAVs) are designed to be aerodynamically efficient, allowing them
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The rapid growth of drone use in urban areas has prompted authorities to review airspace regulations, forcing drone manufacturers to anticipate and reduce the noise emissions during the design stage. Additionally, micro air vehicles (MAVs) are designed to be aerodynamically efficient, allowing them to fly farther, longer and safer. In this study, a steady aerodynamic code and an acoustic propagator based on the non-linear vortex lattice method (NVLM) and Farassat’s formulation-1A of the Ffowcs Williams and Hawkings (FW-H) acoustic analogy, respectively, are coupled with pymoo, a python-based optimization framework. This tool is used to perform a multi-objective (noise and aerodynamic efficiency) optimization of a 20 cm diameter two-bladed rotor under hovering conditions. From the set of optimized results, (i.e., the Pareto front), three different rotors are 3D-printed using a stereolithography (SLA) technique and tested in an anechoic room. Here, an array of far-field microphones captures the acoustic radiation and directivity of the rotor, while a balance measures the aerodynamic performance. Both the aerodynamic and aeroacoustic performance of the three different rotors, in line with what has been predicted by the numerical codes, are compared and guidelines for the design of aerodynamically and aeroacoustically efficient MAV rotors are extracted.
Full article
(This article belongs to the Special Issue Aerodynamics and Aeroacoustics of Micro Air Vehicles)
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Open AccessArticle
Numerical Simulation of Swept-Wing Laminar–Turbulent Flow in the Presence of Two-Dimensional Surface Reliefs
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Andrey V. Boiko, Stanislav V. Kirilovskiy and Tatiana V. Poplavskaya
Fluids 2024, 9(4), 95; https://doi.org/10.3390/fluids9040095 - 19 Apr 2024
Abstract
Stochastization of boundary-layer flow has a dramatic effect on the aerodynamic characteristics of wings, nacelles, and other objects frequently encountered in practice, resulting in higher skin-friction drag and worse aerodynamic quality. A swept-wing boundary layer encountering a transition to turbulence in the presence
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Stochastization of boundary-layer flow has a dramatic effect on the aerodynamic characteristics of wings, nacelles, and other objects frequently encountered in practice, resulting in higher skin-friction drag and worse aerodynamic quality. A swept-wing boundary layer encountering a transition to turbulence in the presence of two-dimensional surface reliefs is considered. The relief has the form of strips of a rectangular cross-section oriented parallel to the leading edge and located at different distances from it. The computations are performed for the angle of attack of −5° and an incoming flow velocity of 30 m/s using the ANSYS Fluent 18.0 software together with the author’s LOTRAN 3 package for predicting the laminar–turbulent transition on the basis of the -method. New data on distributions of N factors of swept-wing cross-flow instability affected by the surface relief are presented. The data are of practical importance for engineering modeling of the transition. Also, the effectiveness of using the reliefs as a passive method of weakening the cross-flow instability up to 30% to delay the flow stochastization is shown.
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(This article belongs to the Special Issue Stochastic Equations in Fluid Dynamics, 2nd Edition)
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Open AccessArticle
Darcy–Brinkman Model for Ternary Dusty Nanofluid Flow across Stretching/Shrinking Surface with Suction/Injection
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Sudha Mahanthesh Sachhin, Ulavathi Shettar Mahabaleshwar, David Laroze and Dimitris Drikakis
Fluids 2024, 9(4), 94; https://doi.org/10.3390/fluids9040094 - 18 Apr 2024
Abstract
Understanding of dusty fluids for different Brinkman numbers in porous media is limited. This study examines the Darcy–Brinkman model for two-dimensional magneto-hydrodynamic fluid flow across permeable stretching/shrinking surfaces with heat transfer. Water was considered as a conventional base fluid in which the copper
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Understanding of dusty fluids for different Brinkman numbers in porous media is limited. This study examines the Darcy–Brinkman model for two-dimensional magneto-hydrodynamic fluid flow across permeable stretching/shrinking surfaces with heat transfer. Water was considered as a conventional base fluid in which the copper (Cu), silver (Ag), and titanium dioxide ( ) nanoparticles were submerged in a preparation of a ternary dusty nanofluid. The governing nonlinear partial differential equations are converted to ordinary differential equations through suitable similarity conversions. Under radiation and mass transpiration, analytical solutions for stretching sheets/shrinking sheets are obtained. Several parameters are investigated, including the magnetic field, Darcy–Brinkman model, solution domain, and inverse Darcy number. The outcomes of the present article reveal that increasing the Brinkman number and inverse Darcy number decreases the velocity of the fluid and dusty phase. Increasing the magnetic field decreases the momentum of the boundary layer. Ternary dusty nanofluids have significantly improved the heat transmission process for manufacturing with applications in engineering, and biological and physical sciences. The findings of this study demonstrate that the ternary nanofluid phase’s heat and mass transpiration performance is better than the dusty phase’s performance.
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(This article belongs to the Topic Advanced Heat and Mass Transfer Technologies)
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Open AccessArticle
Real-Time Optimal Flow Setting and Respiratory Profile Evaluation in Infants Treated with High-Flow Nasal Cannula (HFNC)
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Francesco Montecchia and Paola Papoff
Fluids 2024, 9(4), 93; https://doi.org/10.3390/fluids9040093 - 18 Apr 2024
Abstract
High-flow nasal cannula (HFNC) is becoming the gold standard to treat respiratory distress at any age since it potentially provides several significant clinical advantages. An obstacle to the diffusion of this simple and effective system of oxygen therapy is the impossibility to know
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High-flow nasal cannula (HFNC) is becoming the gold standard to treat respiratory distress at any age since it potentially provides several significant clinical advantages. An obstacle to the diffusion of this simple and effective system of oxygen therapy is the impossibility to know the optimal flow rate leading to such advantages that allows the reduction in the respiratory effort without causing hyperinflation. To assist clinicians during HFNC treatment in setting the optimal flow rate and in determining the most relevant parameters related to respiratory mechanics and the effort of the patient, we developed a new programmable data monitoring, acquisition, and elaborating system (Pro_HFNC). The application of Pro_HFNC is fully compatible with HFNC as it is interfaced with patient through a facial mask and two specific catheters. The unavoidable and unpredictable loss of air flow occurring around the contour of the mask is evaluated and compensated by a specific algorithm implemented by Pro_HFNC. Our preliminary clinical trials on pediatric patients treated with HFNC show that Pro_HFNC is actually capable to detect for any specific patient both the lower threshold of the delivered flow beyond which the benefits of HFNC application are reached and all the parameters useful for a complete evaluation of the respiratory profile. Pro_HFNC can really help physicians in setting the optimal flow rate during HFNC treatment, thus allowing for the most effective HFNC performance.
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(This article belongs to the Special Issue Respiratory Flows)
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Unsteady Subsonic/Supersonic Flow Simulations in 3D Unstructured Grids over an Acoustic Cavity
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Guillermo Araya
Fluids 2024, 9(4), 92; https://doi.org/10.3390/fluids9040092 - 17 Apr 2024
Abstract
In this study, the unsteady Reynolds-averaged Navier–Stokes (URANS) equations are employed in conjunction with the Menter Shear Stress Transport (SST)-Scale-Adaptive Simulation (SAS) turbulence model in compressible flow, with an unstructured mesh and complex geometry. While other scale-resolving approaches in space and time, such
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In this study, the unsteady Reynolds-averaged Navier–Stokes (URANS) equations are employed in conjunction with the Menter Shear Stress Transport (SST)-Scale-Adaptive Simulation (SAS) turbulence model in compressible flow, with an unstructured mesh and complex geometry. While other scale-resolving approaches in space and time, such as direct numerical simulation (DNS) and large-eddy simulation (LES), supply more comprehensive information about the turbulent energy spectrum of the fluctuating component of the flow, they imply computationally intensive situations, usually performed over structured meshes and relatively simple geometries. In contrast, the SAS approach is designed according to “physically” prescribed length scales of the flow. More precisely, it operates by locally comparing the length scale of the modeled turbulence to the von Karman length scale (which depends on the local first- and second fluid velocity derivatives). This length-scale ratio allows the flow to dynamically adjust the local eddy viscosity in order to better capture the large-scale motions (LSMs) in unsteady regions of URANS simulations. While SAS may be constrained to model only low flow frequencies or wavenumbers (i.e., LSM), its versatility and low computational cost make it attractive for obtaining a quick first insight of the flow physics, particularly in those situations dominated by strong flow unsteadiness. The selected numerical application is the well-known M219 three-dimensional rectangular acoustic cavity from the literature at two different free-stream Mach numbers, (0.85 and 1.35) and a length-to-depth ratio of 5:1. Thus, we consider the “deep configuration” in experiments by Henshaw. The SST-SAS model demonstrates a satisfactory compromise between simplicity, accuracy, and flow physics description.
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(This article belongs to the Special Issue Recent Advances in Aerodynamics and Aeroacoustics: Towards Greener Aviation)
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Open AccessArticle
Computational Fluid Dynamics Prediction of External Thermal Loads on Film-Cooled Gas Turbine Vanes: A Validation of Reynolds-Averaged Navier–Stokes Transition Models and Scale-Resolving Simulations for the VKI LS-94 Test Case
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Simone Sandrin, Lorenzo Mazzei, Riccardo Da Soghe and Fabrizio Fontaneto
Fluids 2024, 9(4), 91; https://doi.org/10.3390/fluids9040091 - 15 Apr 2024
Abstract
Given the increasing role of computational fluid dynamics (CFD) simulations in the aerothermal design of gas turbine vanes and blades, their rigorous validation is becoming more and more important. This article exploits an experimental database obtained by the von Karman Institute (VKI) for
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Given the increasing role of computational fluid dynamics (CFD) simulations in the aerothermal design of gas turbine vanes and blades, their rigorous validation is becoming more and more important. This article exploits an experimental database obtained by the von Karman Institute (VKI) for Fluid Dynamics for the LS-94 test case. This represents a film-cooled transonic turbine vane, investigated in a five-vane linear cascade configuration under engine-like conditions in terms of the Reynolds number and Mach number. The experimental characterization included inlet freestream turbulence measured with hot-wire anemometry, aerodynamic performance assessed with a three-hole pressure probe in the downstream section, and vane convective heat transfer coefficient distribution determined with thin-film thermometers. The test matrix included cases without any film-cooling injection, pressure-side injection, and suction-side injection. The CFD simulations were carried out in Ansys Fluent, considering the impact of mesh sizing and steady-state Reynolds-Averaged Navier-Stokes (RANS) transition modelling, as well as more accurate transient scale-resolving simulations. This work provides insight into the advantages and drawbacks of such approaches for gas turbine hot-gas path designers.
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(This article belongs to the Special Issue Computational Fluid Dynamics in Fluid Machinery)
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Open AccessArticle
A Compressible Formulation of the One-Fluid Model for Two-Phase Flows
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Simon El Ouafa, Stephane Vincent, Vincent Le Chenadec, Benoît Trouette, Syphax Fereka and Amine Chadil
Fluids 2024, 9(4), 90; https://doi.org/10.3390/fluids9040090 - 12 Apr 2024
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In this paper, we introduce a compressible formulation for dealing with 2D/3D compressible interfacial flows. It integrates a monolithic solver to achieve robust velocity–pressure coupling, ensuring precision and stability across diverse fluid flow conditions, including incompressible and compressible single-phase and two-phase flows. Validation
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In this paper, we introduce a compressible formulation for dealing with 2D/3D compressible interfacial flows. It integrates a monolithic solver to achieve robust velocity–pressure coupling, ensuring precision and stability across diverse fluid flow conditions, including incompressible and compressible single-phase and two-phase flows. Validation of the model is conducted through various test scenarios, including Sod’s shock tube problem, isothermal viscous two-phase flows without capillary effects, and the impact of drops on viscous liquid films. The results highlight the ability of the scheme to handle compressible flow situations with capillary effects, which are important in computational fluid dynamics (CFD).
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(This article belongs to the Section Mathematical and Computational Fluid Mechanics)
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Numerical Analysis of Convective Heat Transfer in Quenching Treatments of Boron Steel under Different Configurations of Immersed Water Jets and Its Effects on Microstructure
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Raúl Alberto Tinajero-Álvarez, Constantin Alberto Hernández-Bocanegra, José Ángel Ramos-Banderas, Nancy Margarita López-Granados, Brandon Farrera-Buenrostro, Enrique Torres-Alonso and Gildardo Solorio-Díaz
Fluids 2024, 9(4), 89; https://doi.org/10.3390/fluids9040089 - 11 Apr 2024
Abstract
In this work, the effects of jet impact angle and water flow on the heat-transfer coefficient in boron steel probes were analyzed. Angles of 90°, 75° and 60° were used with stirring flows of 33 l·min−1, 25 l·min−1, 13
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In this work, the effects of jet impact angle and water flow on the heat-transfer coefficient in boron steel probes were analyzed. Angles of 90°, 75° and 60° were used with stirring flows of 33 l·min−1, 25 l·min−1, 13 l·min−1 and 6 l·min−1. The aim consisted of determining the heat-extraction rates by analyzing the correlation programmed in the Ansys Fluent 2020R2 software when different cooling conditions are used, avoiding many experiments, and establishing quenching conditions free of surface defects on the workpiece. This process is currently used in heavy machinery, requiring high hardness and wear resistance. The fluid-dynamic field was validated using a scale physical model using the particle image velocimetry technique, PIV. In contrast, the thermal field was validated with transient state experiments solving the inverse heat conduction problem, IHCP. The results show that for high flows (33 l·min−1), the jets with an angle of 90° impact the entire surface of the piece, but their cooling rate is slower compared to the other angles, being 243.61 K·s−1, and 271.70 K·s−1, 329.56 K·s−1 for 75° and 60°, respectively. However, for low flows (6 l·min−1), the impact velocities are very similar for the three cases, promoting more homogeneous cooling rates of 58.47 K·s−1, 73.58 K·s−1 and 63.98 K s−1 for angles of 90°, 75° and 60°, respectively. Likewise, through the use of CCT diagrams, it was determined that regardless of the cooling rate, the final structure will always be a mixture of martensite–bainite due to the effect of boron as determined experimentally, which implies a more significant proportion of martensite at higher cooling rates.
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(This article belongs to the Special Issue Phase Change and Convective Heat Transfer)
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Open AccessArticle
Deep Reinforcement Learning-Augmented Spalart–Allmaras Turbulence Model: Application to a Turbulent Round Jet Flow
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Lukas M. Fuchs, Jakob G. R. von Saldern, Thomas L. Kaiser and Kilian Oberleithner
Fluids 2024, 9(4), 88; https://doi.org/10.3390/fluids9040088 - 09 Apr 2024
Abstract
The purpose of this work is to explore the potential of deep reinforcement learning (DRL) as a black-box optimizer for turbulence model identification. For this, we consider a Reynolds-averaged Navier–Stokes (RANS) closure model of a round turbulent jet flow at a Reynolds number
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The purpose of this work is to explore the potential of deep reinforcement learning (DRL) as a black-box optimizer for turbulence model identification. For this, we consider a Reynolds-averaged Navier–Stokes (RANS) closure model of a round turbulent jet flow at a Reynolds number of 10,000. For this purpose, we augment the widely utilized Spalart–Allmaras turbulence model by introducing a source term that is identified by DRL. The algorithm is trained to maximize the alignment of the augmented RANS model velocity fields and time-averaged large eddy simulation (LES) reference data. It is shown that the alignment between the reference data and the results of the RANS simulation is improved by 48% using the Spalart–Allmaras model augmented with DRL compared to the standard model. The velocity field, jet spreading rate, and axial velocity decay exhibit substantially improved agreement with both the LES reference and literature data. In addition, we applied the trained model to a jet flow with a Reynolds number of 15,000, which improved the mean field alignment by 35%, demonstrating that the framework is applicable to unseen data of the same configuration at a higher Reynolds number. Overall, this work demonstrates that DRL is a promising method for RANS closure model identification. Hurdles and challenges associated with the presented methodology, such as high numerical cost, numerical stability, and sensitivity of hyperparameters are discussed in the study.
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(This article belongs to the Section Mathematical and Computational Fluid Mechanics)
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Open AccessArticle
Discrete and Continuous Adjoint-Based Aerostructural Wing Shape Optimization of a Business Jet
by
Konstantinos Tsiakas, Xenofon Trompoukis, Varvara Asouti, Kyriakos Giannakoglou, Gilbert Rogé, Sarah Julisson, Ludovic Martin and Steven Kleinveld
Fluids 2024, 9(4), 87; https://doi.org/10.3390/fluids9040087 - 05 Apr 2024
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This article presents single- and multi-disciplinary shape optimizations of a generic business jet wing at two transonic cruise flow conditions. The studies performed are based on two high-fidelity gradient-based optimization tools, assisted by the adjoint method (following both discrete and continuous approaches). Single
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This article presents single- and multi-disciplinary shape optimizations of a generic business jet wing at two transonic cruise flow conditions. The studies performed are based on two high-fidelity gradient-based optimization tools, assisted by the adjoint method (following both discrete and continuous approaches). Single discipline and coupled multi-disciplinary sensitivity derivatives computed from the two tools are compared and verified against finite differences. The importance of not making the frozen turbulence assumption in adjoint-based optimization is demonstrated. Then, a number of optimization runs, ranging from a pure aerodynamic with a rigid structure to an aerostructural one exploring the trade-offs between the involved disciplines, are presented and discussed. The middle-ground scenario of optimizing the wing with aerodynamic criteria and, then, performing an aerostructural trimming is also investigated.
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Open AccessArticle
Study of the Geometry of an Oscillating Water Column Device with Five Chambers Coupled under Regular Waves through the Constructal Design Method
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Yuri Theodoro Barbosa de Lima, Liércio André Isoldi, Elizaldo Domingues dos Santos, Bianca Neves Machado, Mateus das Neves Gomes, Cesare Biserni and Luiz Alberto Oliveira Rocha
Fluids 2024, 9(4), 86; https://doi.org/10.3390/fluids9040086 - 05 Apr 2024
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This research conducts a numerical study of a wave energy converter (WEC) device with five coupled hydropneumatic chambers, operating based on the principle of an oscillating water column (OWC). A turbine was not included, only considering the tube without it. The computational domain
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This research conducts a numerical study of a wave energy converter (WEC) device with five coupled hydropneumatic chambers, operating based on the principle of an oscillating water column (OWC). A turbine was not included, only considering the tube without it. The computational domain was defined by a wave channel housing an OWC device subjected to regular incident waves. The central objective was to assess the impact of chamber geometry on maximizing the total hydropneumatic power in energy conversion. The numerical simulations consider the pressure, mass flow rate, and total hydropneumatic power, with the latter being the performance indicator. To determine the geometries to be analyzed, the Constructal Design method was employed in conjunction with the exhaustive search optimization method to maximize the performance indicator. The degrees of freedom defined were the ratios between the height (Hn) and the length (Ln) of the hydropneumatic chambers (Hn/Ln, where n varies from one to five). Based on the results of the mass flow rate and pressure, their influence on power was evaluated. It was observed that the influence of the degrees of freedom on the pressure difference, mass flow rate, and hydrodynamic power was quite similar, displaying an increase for low ratios of Hn/Ln up to a maximum magnitude and followed by a decrease in magnitude. The best performance was achieved for the geometric configuration with Hn/Ln = 0.2613 (Hn = 5.0625 m and Ln = 15.8219 m), representing an improvement of 98.6% compared to the worst case analyzed.
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Open AccessArticle
Computational Analysis of Blood Flow in Healthy Pulmonary Arteries in Comparison to Repaired Tetralogy of Fallot Results: A Small Cohort Study
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Maria Boumpouli, Scott MacDonald Black and Asimina Kazakidi
Fluids 2024, 9(4), 85; https://doi.org/10.3390/fluids9040085 - 01 Apr 2024
Abstract
Characterization of the physiological hemodynamic environment in normal pulmonary arteries is a key factor in understanding pathological conditions. This study aimed to analyze the morphology and hemodynamics in the healthy adult pulmonary bifurcation in comparison to age-matched repaired Tetralogy of Fallot (rTOF) geometries.
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Characterization of the physiological hemodynamic environment in normal pulmonary arteries is a key factor in understanding pathological conditions. This study aimed to analyze the morphology and hemodynamics in the healthy adult pulmonary bifurcation in comparison to age-matched repaired Tetralogy of Fallot (rTOF) geometries. The pulmonary trunk of five healthy volunteers was reconstructed from 4D Flow-MRI data and was compared to rTOF results. Subject-specific boundary conditions were assigned in both the inlet and outlets of the models, and flow characteristics were analyzed computationally. The morphological and flow features were consistent among the healthy geometries, highlighting the ability of an averaged geometry derived from this small cohort to capture the main flow characteristics. A slightly higher mean time-averaged wall shear stress (TAWSS) was found in the right pulmonary artery, which was also the branch with a higher mean curvature and local Reynolds number. Compared to rTOF results, the averaged healthy geometry demonstrated more than an 8-fold lower value in TAWSS, with the individual patient-specific healthy volunteers showing further reduced TAWSS than the rTOF patients. These observations could be useful in clinical assessment and decision making based on hemodynamic indices.
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(This article belongs to the Special Issue Advances in Hemodynamics and Related Biological Flows)
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Turbulent Flow Prediction-Simulation: Strained Flow with Initial Isotropic Condition Using a GRU Model Trained by an Experimental Lagrangian Framework, with Emphasis on Hyperparameter Optimization
by
Reza Hassanian, Marcel Aach, Andreas Lintermann, Ásdís Helgadóttir and Morris Riedel
Fluids 2024, 9(4), 84; https://doi.org/10.3390/fluids9040084 - 01 Apr 2024
Abstract
This study presents a novel approach to using a gated recurrent unit (GRU) model, a deep neural network, to predict turbulent flows in a Lagrangian framework. The emerging velocity field is predicted based on experimental data from a strained turbulent flow, which was
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This study presents a novel approach to using a gated recurrent unit (GRU) model, a deep neural network, to predict turbulent flows in a Lagrangian framework. The emerging velocity field is predicted based on experimental data from a strained turbulent flow, which was initially a nearly homogeneous isotropic turbulent flow at the measurement area. The distorted turbulent flow has a Taylor microscale Reynolds number in the range of 100 < < 152 before creating the strain and is strained with a mean strain rate of 4 in the Y direction. The measurement is conducted in the presence of gravity consequent to the actual condition, an effect that is usually neglected and has not been investigated in most numerical studies. A Lagrangian particle tracking technique is used to extract the flow characterizations. It is used to assess the capability of the GRU model to forecast the unknown turbulent flow pattern affected by distortion and gravity using spatiotemporal input data. Using the flow track’s location (spatial) and time (temporal) highlights the model’s superiority. The suggested approach provides the possibility to predict the emerging pattern of the strained turbulent flow properties observed in many natural and artificial phenomena. In order to optimize the consumed computing, hyperparameter optimization (HPO) is used to improve the GRU model performance by 14–20%. Model training and inference run on the high-performance computing (HPC) JUWELS-BOOSTER and DEEP-DAM systems at the Jülich Supercomputing Centre, and the code speed-up on these machines is measured. The proposed model produces accurate predictions for turbulent flows in the Lagrangian view with a mean absolute error (MAE) of 0.001 and an score of 0.993.
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(This article belongs to the Special Issue Turbulent Flow, 2nd Edition)
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Characterization of Oscillatory Response of Light-Weight Wind Turbine Rotors under Controlled Gust Pulses
by
Fernando Ponta, Alayna Farrell, Apurva Baruah and North Yates
Fluids 2024, 9(4), 83; https://doi.org/10.3390/fluids9040083 - 26 Mar 2024
Abstract
Given the industry-wide trend of continual increases in the size of utility-scale wind turbines, a point will come where reductions will need to be made in terms of the weight of the turbine’s blades to ensure they can be as long as needed
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Given the industry-wide trend of continual increases in the size of utility-scale wind turbines, a point will come where reductions will need to be made in terms of the weight of the turbine’s blades to ensure they can be as long as needed without sacrificing structural stability. One such technique that may be considered is to decrease the material used for the shell and spar cap. While this will solve the weight issue, it creates a new one entirely—less material for the shell and spar cap will in turn create blades that are more flexible than what is currently used. This article aims to investigate how the oscillatory response of light-weight wind turbine rotors is affected by these flexibility changes. The object of our study is the Sandia National Lab National Rotor Testbed (SNL-NRT) wind turbine, which the authors investigated in the course of a research project supported by SNL. Using a reduced-order characterization (ROC) technique based on controlled gust pulses, introduced by the authors in a previous work, the aeroelastic dynamics of the NRT’s original baseline blade design and several of its flexible variations were studied via numerical simulations employing the CODEF multiphysics suite. Results for this characterization are presented and analyzed, including a generalization of the ROC of the SNL-NRT oscillatory dynamics to larger machines with geometrical similarity. The latter will prove to be valuable in terms of extrapolating results from the present investigation and other ongoing studies to the scale of current and future commercial machines.
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(This article belongs to the Special Issue Computational Fluid Dynamics in Fluid Machinery)
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