Next Issue
Volume 11, March
Previous Issue
Volume 11, January
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
4.0
1.8
Journals
Fluids
Volume 11
Issue 2
share announcement

Fluids, Volume 11, Issue 2 (February 2026) – 31 articles

Cover Story (view full-size image): Predicting pressure and lift for supersonic asymmetric delta wings at high angles of attack remains beyond classical linear theory. This study presents a simple algebraic method bridging linear solutions and nonlinear shock physics via geometric transformation. By reformulating the linear pressure expression into a geometrically invariant form and replacing 2D flow regions with exact oblique shock relations, the model yields explicit formulas for pressure distribution and normal force coefficient—without costly simulations or complex expansions. Validated against symmetric and yawed delta wings, it captures nonlinear effects with acceptable accuracy, showing how classical ideas, reimagined through geometric similarity, provide useful tools for modern supersonic design. View this paper
  • Issues are regarded as officially published after their release is announced to the table of contents alert mailing list.
  • You may sign up for e-mail alerts to receive table of contents of newly released issues.
  • PDF is the official format for papers published in both, html and pdf forms. To view the papers in pdf format, click on the "PDF Full-text" link, and use the free Adobe Reader to open them.
Order results
Result details
Section
Show export options expand_more Show export options expand_less
Select all
Export citation of selected articles as:
19 pages, 3857 KB  
Article
Aerodynamic Analysis and Design of a Sliding Drag Reduction System Using Graph Neural Networks
by Shinji Kajiwara and Cinto Ton
Fluids 2026, 11(2), 59; https://doi.org/10.3390/fluids11020059 - 22 Feb 2026
Viewed by 727
Abstract
To maximize competitive performance in motorsports, balancing high downforce for cornering with low drag for straight–line speed is essential. This paper presents the development and optimization of a sliding Drag Reduction System (DRS) integrated with a ducktail guide for a Student Formula racing [...] Read more.
To maximize competitive performance in motorsports, balancing high downforce for cornering with low drag for straight–line speed is essential. This paper presents the development and optimization of a sliding Drag Reduction System (DRS) integrated with a ducktail guide for a Student Formula racing car. To overcome the computational costs and time constraints of conventional CFD–based iterative design, a Graph Neural Network (GNN) surrogate model was developed to predict aerodynamic coefficients. Unlike traditional models, the GNN directly learns from the geometric graph structure of the multi–element wing, enabling near–instantaneous and highly accurate predictions. CFD results indicated that activating the DRS reduced drag from 82.68 N to 25.51 N, improving the lift–to–drag ratio from 1.67 to 2.67. The GNN surrogate model achieved an R2 value exceeding 0.99, demonstrating exceptional predictive fidelity compared to high–resolution simulations. Physical track testing with a Formula SAE vehicle corroborated these findings, showing a 4.6% improvement in 50 m acceleration and a 5.8% increase in maximum speed. This research establishes that GNN–based surrogate models can significantly accelerate the design and optimization of complex variable aerodynamic systems, providing a robust framework for performance enhancement in racing applications. Full article
(This article belongs to the Special Issue Machine Learning and Artificial Intelligence in Fluid Mechanics, 2nd Edition)
►▼ Show Figures

Figure 1

21 pages, 5494 KB  
Article
Parametric Study of Wake Concentration from the Instantaneous Release of a Dense Fluid Upstream of a Cubic Obstacle
by Romana Akhter and Nigel B. Kaye
Fluids 2026, 11(2), 58; https://doi.org/10.3390/fluids11020058 - 20 Feb 2026
Viewed by 236
Abstract
Experimental results are reported to explore the role of release location and release volume on the dispersion of a dense gas cloud around an isolated cubic building. The experiments are analogous to the Thorney Island dense gas dispersion field tests, and the results [...] Read more.
Experimental results are reported to explore the role of release location and release volume on the dispersion of a dense gas cloud around an isolated cubic building. The experiments are analogous to the Thorney Island dense gas dispersion field tests, and the results are qualitatively similar to those of the full-scale tests. Water bath experiments were used in this study with fresh water in a flume representing the atmospheric wind and dyed saltwater representing the dense gas. Results are presented for different relative density flows, quantified using the Richardson number (Ri), for five different release volumes ranging from 10% to 60% of the building volume. Results are also presented for different upstream release distances ranging from 50% to 150% of the building height. Measurements show that there is a complex interaction between release volume, release distance, and Richardson number, and the resulting flow over and around the building. For releases close to the building, the cloud has little distance over which to adjust before being swept around the building and into the building wake. However, for larger release distances, there is adequate distance for the cloud to adjust, with the nature of the adjustment being a function of the Richardson number. For small Ri (low density difference), the cloud spreads out as it moves downstream, mixes with the ambient fluid, and increases in volume such that the volume of the cloud interacting with the building is larger than the initial release. For higher Ri flows (larger density difference), the dense cloud collapses down onto the channel bed, where it spreads out radially as it is advected downstream. The clouds are, therefore, much shallower than the building height when they collide with the building. This competition between the collapse of the cloud and its advection downstream is parameterized using a novel ‘adjusted Richardson number’ Ri*. Full article
(This article belongs to the Section Geophysical and Environmental Fluid Mechanics)
►▼ Show Figures

Figure 1

18 pages, 3889 KB  
Article
Influence of Structural Height on the Thermo-Hydraulic Performance of a Water-Cooled Gyroid Heat Sink
by Mohamad Ziad Saghir and Mohammad Mansur Rahman
Fluids 2026, 11(2), 57; https://doi.org/10.3390/fluids11020057 - 19 Feb 2026
Viewed by 354
Abstract
The triply periodic minimal surface structure is receiving significant attention amongst the engineering community. The advantage of using such a structure is its ability to provide lightweight cooling to surfaces. In this paper, attention is drawn to a gyroid structure composed of a [...] Read more.
The triply periodic minimal surface structure is receiving significant attention amongst the engineering community. The advantage of using such a structure is its ability to provide lightweight cooling to surfaces. In this paper, attention is drawn to a gyroid structure composed of a shell network and a solid network, with a porosity of 0.7. Three different flow rates, using water as the circulating fluid, are experimentally applied to cool a square surface with a base of 37.5 mm and a height of 12.7 mm. It was found that this structure provided a high cooling rate, achieving a Nusselt number around 100 with a solid lattice and 160 for a shell lattice. It is also noted that the TPMS area plays a significant role, thereby increasing the cooling rate. When the TPMS height is 90% of the initial height of 12.7 mm, the performance of both structures is found to be well accepted. Pressure drop is reduced, and the heat performance is improved. The circulating flow above the structure marginally reduced the pressure drop. The performance evaluation criteria for the shell network ranged from 95 < PEC to < 225, and for the solid network from 125 < PEC to < 155. The optimization method has been applied across the entire height range using response surface methodology. It is found that the optimum TPMS height is for an aspect ratio of 95.1%. Full article
(This article belongs to the Special Issue Thermal Fluids: Theory and Applications)
►▼ Show Figures

Figure 1

14 pages, 5218 KB  
Article
A Novel Polynomial Approach for Particle Image Velocimetry (PIV) Image Reconstruction
by Briana M. Steven and Paul D. Docherty
Fluids 2026, 11(2), 56; https://doi.org/10.3390/fluids11020056 - 18 Feb 2026
Viewed by 319
Abstract
Particle Image Velocimetry (PIV) often utilizes a cross-correlation method to determine how far particles have moved between two captured images. The most common methods for vector estimation use computationally exhaustive cross-correlation functions across the interrogation window and an exhaustive search to find the [...] Read more.
Particle Image Velocimetry (PIV) often utilizes a cross-correlation method to determine how far particles have moved between two captured images. The most common methods for vector estimation use computationally exhaustive cross-correlation functions across the interrogation window and an exhaustive search to find the maximum correlation position. This paper proposes a novel method to vector generation in which a preprocessing blur is applied to the two image before performing a cross-correlation for only nine points. These nine points are used to approximate the original cross-correlation surface as a second-order polynomial surface that can be solved analytically to find the optima point. Three iterations of the process are used for each location converging to a precise optimum. This method is very accurate on computer-generated PIV images and solves the entire vector field faster than the original basic method at any image size. However, the success is limited to in silico PIV data and cannot produce coherent vector fields when applied to experimental data captured on a supra-aortic bypass PIV experiment. This method may find applications in other domains where the input data is closer to the perfect computer-generated particle data. Full article
(This article belongs to the Section Mathematical and Computational Fluid Mechanics)
►▼ Show Figures

Figure 1

26 pages, 7045 KB  
Article
Vortex-Induced Vibrations of a 2DOF Rigid Cylinder with Hard Marine Growth in Turbulent Oscillatory Flow
by Henry Francis Annapeh and Victoria Kurushina
Fluids 2026, 11(2), 55; https://doi.org/10.3390/fluids11020055 - 18 Feb 2026
Viewed by 431
Abstract
This paper presents a numerical investigation into the vortex-induced vibrations (VIV) of a smooth and a marine-fouled circular cylinder with two degrees of freedom (2DOF), subjected to a turbulent oscillatory flow. The study aims to elucidate the critical influence of the Keulegan-Carpenter ( [...] Read more.
This paper presents a numerical investigation into the vortex-induced vibrations (VIV) of a smooth and a marine-fouled circular cylinder with two degrees of freedom (2DOF), subjected to a turbulent oscillatory flow. The study aims to elucidate the critical influence of the Keulegan-Carpenter (KC) number of 5, 10, and 15 on the vibration response, lock-in regime, frequency synchronization, trajectory patterns and vorticity. Simulations are performed by solving the two-dimensional unsteady Reynolds-Averaged Navier–Stokes (RANS) equations with the Shear Stress Transport (SST) k-ω turbulence model in ANSYS Fluent 2025 R1. An increase in the KC number leads to a significant broadening of the lock-in region, an increase in maximum vibration amplitudes and their emergence at higher reduced velocities. Another key finding is the consistent suppressive effect of biofouling on cross-flow vibrations. The biofouled cylinder exhibits lower cross-flow amplitudes across all KC numbers compared to the smooth cylinder, almost plateauing at around 1.0D for KC = 10 and 15, while the smooth cylinder reaches amplitudes of up to 1.8D and a maximum in-line amplitude of 4.46D. These findings have critical implications for the realistic fatigue life assessment and design of offshore marine structures, highlighting the necessity of incorporating surface roughness effects into VIV prediction models. Full article
(This article belongs to the Special Issue Vortex Dynamics)
►▼ Show Figures

Figure 1

30 pages, 12498 KB  
Article
Vortex Structure and Aerodynamic Loads of a Pentagonal Heliostat for Concentrating Solar Power: A CFD Study
by Erhan Huang, Ying Chang, Yangzhao Liu, Kaoshan Dai and Peng Chen
Fluids 2026, 11(2), 54; https://doi.org/10.3390/fluids11020054 - 17 Feb 2026
Viewed by 947
Abstract
Heliostats constitute essential elements within concentrating solar power (CSP), where their structure, load profiles, and operational environment render wind loads a critical factor in their design considerations, as these loads directly impact the cost of energy generation. The aerodynamics significantly influence wind-induced effects, [...] Read more.
Heliostats constitute essential elements within concentrating solar power (CSP), where their structure, load profiles, and operational environment render wind loads a critical factor in their design considerations, as these loads directly impact the cost of energy generation. The aerodynamics significantly influence wind-induced effects, resulting in considerable variability in wind loads among different heliostat geometries. This study utilizes the Computational Fluid Dynamics (CFD) methodology to systematically examine the aerodynamic behavior of an isolated pentagonal heliostat. Employing the Unsteady Reynolds-Averaged Navier–Stokes (URANS) equations with an atmospheric boundary layer inlet condition, the investigation focuses on the flow field and wind load characteristics at four representative pitch angles: 0° (stow position), 30°, 60°, and 90°. Findings indicate that the pitch angle exerts a decisive impact on flow separation patterns. Specifically, as the elevation angle decreases, the flow regime shifts from being predominantly influenced by the mirror surface to being governed by the support structure, mediated through an interactive coupling between these components. At the 60° operational pitch angle, the pentagonal heliostat’s distinctive corner geometry induces an asymmetric vortex configuration—characterized by a smaller vortex at the top and a larger one at the bottom—thereby disrupting the conventional vortex distribution observed in symmetric heliostat designs. A further analysis of wind load characteristics indicates that, compared to a quadrilateral heliostat, the pentagonal mirror exhibits a significantly lower Elevation Moment Coefficient, despite a slight increase in the normal force coefficient. This reduction is attributed to a balancing mechanism: the “vortex structure asymmetry” creates an upper-large–lower-small distribution of absolute negative pressure on the support surface, while the “stagnation point position” shift with elevation angle produces an upper-small–lower-large distribution of absolute positive pressure on the reflector. The interaction between these opposing trends minimizes the net pressure differential across the mirror height, thereby contributing to superior overall aerodynamic performance. The reduction in the elevation moment coefficient contributes to enhanced structural wind resistance, thereby improving the overall energy efficiency and economic viability of concentrating solar power. Full article
►▼ Show Figures

Figure 1

26 pages, 7165 KB  
Article
A Robust Hybrid Staggered/Collocated Mesh Scheme for CFD on Skewed Meshes
by Raad Issa and Giovanni Giustini
Fluids 2026, 11(2), 53; https://doi.org/10.3390/fluids11020053 - 14 Feb 2026
Viewed by 491
Abstract
In this study, a finite-volume computational fluid dynamics (CFD) technique for application on skewed meshes using staggered pressure nodes is proposed. The method is based on the derivation of a momentum equation for the cell face velocities from appropriately discretised momentum equations in [...] Read more.
In this study, a finite-volume computational fluid dynamics (CFD) technique for application on skewed meshes using staggered pressure nodes is proposed. The method is based on the derivation of a momentum equation for the cell face velocities from appropriately discretised momentum equations in the two cells surrounding the cell face with the driving pressure difference pertaining to the staggered adjacent nodes. In this way, a staggered mesh-like method is obtained that would prevent the occurrence of oscillatory behaviour in pressure or velocity fields. The cell-face velocities are then forced to obey continuity via an equation for pressure akin to other standard CFD schemes. This article describes the formulation of the cell-face momentum equation as well as the way the nodal velocity is reconstructed from the surrounding cell-face velocities. The method is demonstrated to recover the advantages of the PISO solution algorithm that were diminished in implementations in collocated schemes. It is also validated on a reference two-dimensional, steady viscous flow case on both rectangular and skewed meshes to verify its accuracy. It is then applied to the case of an unsteady vortex-shedding flow past a square obstacle, on both rectangular and skewed meshes, and the results are compared with a solution obtained from a collocated method as well as with an experimental value of the Strouhal number. Full article
(This article belongs to the Section Mathematical and Computational Fluid Mechanics)
►▼ Show Figures

Figure 1

20 pages, 7392 KB  
Article
A Vortex-Induced Correction Method for Pressure Loss Prediction in Fluid Network Theory
by Xiaoping Wang, Liqiang Liang, Qingsong Song, Yunguang Ji, Mingxu Sun and Hongtao Li
Fluids 2026, 11(2), 52; https://doi.org/10.3390/fluids11020052 - 14 Feb 2026
Viewed by 377
Abstract
Traditional fluid network theory often underestimates pressure losses in complex pipe-bundle systems operating under vortex-dominated flow conditions, with deviations exceeding 20% in many cases. To address this limitation, this study proposes a vortex-based correction method. Three-dimensional simulations were performed on a multidirectional parallel [...] Read more.
Traditional fluid network theory often underestimates pressure losses in complex pipe-bundle systems operating under vortex-dominated flow conditions, with deviations exceeding 20% in many cases. To address this limitation, this study proposes a vortex-based correction method. Three-dimensional simulations were performed on a multidirectional parallel pipe bundle to analyze vortex formation and to quantify the effects of fluid properties (viscosity and inlet velocity) and structural parameters (branch diameter, manifold cross-sectional ratio, and manifold arrangement) on pressure loss. To account for vortex-induced energy dissipation that is overlooked by conventional one-dimensional network models, an additional vortex-induced loss coefficient, α, is introduced to modify the pressure-loss formulation. Results indicate that higher viscosity, larger branch diameter, a higher manifold cross-sectional ratio, and a co-flow arrangement improve flow uniformity and prediction accuracy. Conversely, higher inlet velocities and counter-flow arrangements intensify vortex effects and increase prediction deviations. Least-squares fitting indicates that α ranges from 1.15 to 1.37. Implementation of the proposed correction reduces pressure-loss prediction errors to within 5%, demonstrating the method’s effectiveness and extending the applicability of fluid network theory to vortex-dominated flows. Full article
(This article belongs to the Special Issue Industrial CFD and Fluid Modelling in Engineering, 3rd Edition)
►▼ Show Figures

Figure 1

30 pages, 2478 KB  
Article
Analytical Modeling of Transverse and Longitudinal Motion of Single Particles in a Horizontal Boundary Layer with Cross-Flow Velocity Pulsations
by Rumen Yankov, Ventsislav Dimitrov, Georgi Tonkov, Veselina Dimitrova, Sylvester Bozherikov, Gergana Tonkova and Konstantin Raykov
Fluids 2026, 11(2), 51; https://doi.org/10.3390/fluids11020051 - 13 Feb 2026
Viewed by 477
Abstract
This study develops an analytical description of the motion of dilute solid particles in the boundary layer of laminar horizontal flows subjected to weak transverse pulsations. The analysis is formulated for dilute spherical solid particles subjected to transverse velocity pulsations in a laminar [...] Read more.
This study develops an analytical description of the motion of dilute solid particles in the boundary layer of laminar horizontal flows subjected to weak transverse pulsations. The analysis is formulated for dilute spherical solid particles subjected to transverse velocity pulsations in a laminar boundary-layer flow. A coupled matrix representation of the governing equations is formulated, and closed-form solutions are obtained using Laplace transformation. The analytical expressions capture transient evolution, forced oscillations, resonance effects, and long-term behaviour for particles with different density ratios. Numerical evaluation shows that light particles migrate toward faster regions of the boundary layer and accelerate longitudinally, while heavy particles move toward slower layers and decelerate. Transverse pulsations generate oscillatory trajectories whose amplitude increases near resonance. Impulsive perturbations superimposed on the continuous motion lead to discontinuous transitions consistent with the linear matrix system. The results provide a unified physical interpretation of particle redistribution mechanisms in boundary layers and offer a compact analytical tool for dilute multiphase flow modelling. Full article
(This article belongs to the Topic Fluid Mechanics, 2nd Edition)
►▼ Show Figures

Figure 1

18 pages, 2616 KB  
Article
Pore-Scale Lattice Boltzmann Simulation of Blind-End Oil Retention
by Huiyu Wang, Yuegang Wang, Qi Lv, Guanghuan Wu and Lijie Liu
Fluids 2026, 11(2), 50; https://doi.org/10.3390/fluids11020050 - 12 Feb 2026
Viewed by 387
Abstract
Currently, a large number of simulation studies on multiphase flow at the pore scale are conducted based on complex porous media. As a microstructure that constitutes the porous media of reservoir, the blind-end can efficiently trap crude oil. However, the research on the [...] Read more.
Currently, a large number of simulation studies on multiphase flow at the pore scale are conducted based on complex porous media. As a microstructure that constitutes the porous media of reservoir, the blind-end can efficiently trap crude oil. However, the research on the multiphase flow within a blind-end is still lacking. In this paper, we used the color-gradient model to simulate the dynamic process that occurs when the oil–water interface passes through a blind-end based on the waterflooding. Furthermore, the effect of influencing factors on the oil in a blind-end (residual oil) after the oil–water interface passes the blind-end were investigated. The results show that the displacement of the water phase from a blind-end full of the oil phase can be categorized into three stages. First, the oil–water interface moves towards the blind-end. Second, when the oil–water interface reaches the blind-end, a portion the of toil phase in the blind-end can be displaced by the water phase. Third, after the oil–water interface passes through the blind-end, a portion of the oil phase (residual oil) is trapped in the blind-end. The residual oil saturation of a blind-end is defined as the ratio of the area of residual oil in a blind-end to the total area of a blind-end. The residual oil saturation in the blind-end increases with the increase in the water velocity, the oil-to-water viscosity ratio, the main channel width, and the blind-end depth. Conversely, it decreases with the increase in blind-end width. The findings provide critical insights into the oil retention mechanism in the blind-end. Full article
(This article belongs to the Special Issue Lattice Boltzmann Methods: Fundamentals and Applications, 2nd Edition)
►▼ Show Figures

Figure 1

19 pages, 5586 KB  
Article
Nonlinear Aerodynamic Load Response and Disaster Mechanism of Sedans in Strong Crosswinds
by Xiaodong Li, Changtao Hu, Jing Zhang, Yuan Ling, Ling Zhang and Afang Jin
Fluids 2026, 11(2), 49; https://doi.org/10.3390/fluids11020049 - 11 Feb 2026
Viewed by 385
Abstract
To address the frequent disasters caused by strong crosswinds in Xinjiang’s “Hundred Miles Wind Zone,” this study utilizes a CFD numerical simulation method, validated by wind tunnel tests with an error of less than 5%, to systematically analyze the nonlinear response characteristics of [...] Read more.
To address the frequent disasters caused by strong crosswinds in Xinjiang’s “Hundred Miles Wind Zone,” this study utilizes a CFD numerical simulation method, validated by wind tunnel tests with an error of less than 5%, to systematically analyze the nonlinear response characteristics of a sedan’s aerodynamic loads under coupled conditions of vehicle speeds ranging from 60 to 100 km/h and crosswinds from 15.5 to 26.5 m/s. The results indicate that the sharp increase in leeward negative pressure, driven by flow separation, governs the escalation of aerodynamic loads. A distinct decoupling is observed between lateral force and drag: while lateral force scales linearly with vehicle speed, aerodynamic drag exhibits a nonlinear hysteresis. This is attributed to a “Flow Alignment Mechanism,” where the reduction in resultant yaw angle improves the leeward streamline topology, thereby mitigating drag growth. Furthermore, the rolling moment is identified as the dominant instability factor (peaking at 551.12 N·m). Conversely, the yawing moment saturates at high speeds due to an “Antagonistic Effect,” wherein dynamic pressure amplification is effectively counteracted by the shortening of the moment arm induced by the rearward migration of the Center of Pressure (CoP). These findings provide a robust theoretical basis for establishing speed limits and stability control strategies in extreme wind zones. Full article
(This article belongs to the Section Geophysical and Environmental Fluid Mechanics)
►▼ Show Figures

Figure 1

21 pages, 6633 KB  
Article
Experimental Study on Water Seepage Characteristics of Saturated Fragmented Coal and Rock Mass
by Dingyi Hao, Jiaxin Huang, Shihao Tu and Long Tang
Fluids 2026, 11(2), 48; https://doi.org/10.3390/fluids11020048 - 11 Feb 2026
Viewed by 272
Abstract
Water inrush disasters continue to plague the advancement of deep underground mining activities. A better understanding of the structural integrity of fragmented geological bodies is crucial to ensuring mining safety. The objective of this study was to accurately reflect the dynamic evolution of [...] Read more.
Water inrush disasters continue to plague the advancement of deep underground mining activities. A better understanding of the structural integrity of fragmented geological bodies is crucial to ensuring mining safety. The objective of this study was to accurately reflect the dynamic evolution of pore structure changes and seepage channels in fragmented coal and rock mass of actual goafs under the coupling effect of mining stress and seepage. The co-evolution laws of the axial strain, nonlinear porosity, and permeability of fragmented coal and rock mass under different particle sizes, gradation characteristics, and stress states were compared, and a stress-pore-water seepage coupling model of the fragmented coal and rock mass was constructed. When subjected to the same axial pressure, the saturated fragmented coal exhibited a higher water permeability than the saturated fragmented rock mass. The greater the particle size, the higher the water permeability of fragmented coal and rock mass. The higher the gradation index, the higher the water permeability of these masses. Their porosity and axial pressure satisfied an exponential attenuation function, whereas their water permeability and axial pressure satisfied the Boltzmann function. The research results can provide theoretical support for preventing and controlling water inrush in goaf areas. Full article
(This article belongs to the Section Geophysical and Environmental Fluid Mechanics)
►▼ Show Figures

Figure 1

21 pages, 1543 KB  
Article
Empirical Model for Predicting the Rheological Properties of Carbonated Slime Pulps
by Rodney Martinez-Rojas, Gerardo Ruiz-Chavarria, Aristides Alejandro Legrá-Lobaina and Leonel Rafael Garcell-Puyans
Fluids 2026, 11(2), 47; https://doi.org/10.3390/fluids11020047 - 9 Feb 2026
Viewed by 369
Abstract
The transport of carbonated slime pulps in pipelines is important for the acid lixiviation process that has developed in the nickel extraction industry in the eastern region of Cuba. This substance is a suspension of fine particles that behaves as a viscoplastic fluid. [...] Read more.
The transport of carbonated slime pulps in pipelines is important for the acid lixiviation process that has developed in the nickel extraction industry in the eastern region of Cuba. This substance is a suspension of fine particles that behaves as a viscoplastic fluid. To address the lack of research conducted on carbonated slime pulps, we carried out an experimental investigation of the rheological properties of this substance over varied operational conditions. As the shear rates involved in the experiments covered more than two orders of magnitude, we fitted the flow curves to the Herschel–Bulkley model, which has been used in the past to model different suspensions. Through data analysis, we observed a transition in rheological behavior at a solid particle concentration of about 30%. Based on the trend of the flow curves, we built an empirical model to predict the rheological properties of slime pulps. In this model, the flow properties of the substance depend on the concentration of solid particles, the pH and the polydispersity index. Our empirical model exhibits high accuracy in predicting the flow properties of carbonated slime pulps. The results can be used to improve the efficiency of industrial processes involving these mineral suspensions. Full article
(This article belongs to the Section Non-Newtonian and Complex Fluids)
►▼ Show Figures

Figure 1

22 pages, 6448 KB  
Article
Experimental Comparison of Unstratified and Stratified Drag Wakes of a Dimpled Sphere at Reynolds Number 105
by Maddie C. Samuell, Nerion Zekaj and Scott Wunsch
Fluids 2026, 11(2), 46; https://doi.org/10.3390/fluids11020046 - 6 Feb 2026
Viewed by 382
Abstract
The drag wake of a dimpled sphere is studied experimentally using stereo particle image velocimetry at a Reynolds number of 105 in both unstratified and stratified (Froude number ≃80) fluids at downstream distances of [...] Read more.
The drag wake of a dimpled sphere is studied experimentally using stereo particle image velocimetry at a Reynolds number of 105 in both unstratified and stratified (Froude number ≃80) fluids at downstream distances of 2≤x/D≤15. More than eighty experiments were conducted, and both analyses of ensemble-mean wakes and statistics of individual experiment wake data are presented. Stratification is found to qualitatively change the ensemble-mean wake axial velocity defect immediately behind the sphere, taking a Gaussian shape without stratification and an oval shape with stratification. As x/D increases, the impact of stratification decreases up to the limit of the data at x/D=15. Analysis of individual experiment wakes indicates that most of the difference between unstratified and stratified ensemble-mean wakes at x/D>10 is because stratification reduces wake meandering in the vertical direction. Full article
(This article belongs to the Section Turbulence)
►▼ Show Figures

Figure 1

21 pages, 5290 KB  
Article
Unsteady Modelling of the Mixing Efficiency, Species Transport, and Flow Structure in a Novel Photochemical Reactor
by Zakaria Mansouri, Richard Jefferson-Loveday, Stephen J. Pickering and Michael W. George
Fluids 2026, 11(2), 45; https://doi.org/10.3390/fluids11020045 - 5 Feb 2026
Viewed by 559
Abstract
This paper deals with computational fluid dynamics (CFD) to improve the design of a new scalable photochemical reactor which uses the Taylor–Couette flow principle. This study aims to investigate the ways to improve the mixing efficiency (Meff) within the reactor, as [...] Read more.
This paper deals with computational fluid dynamics (CFD) to improve the design of a new scalable photochemical reactor which uses the Taylor–Couette flow principle. This study aims to investigate the ways to improve the mixing efficiency (Meff) within the reactor, as it is a key parameter to increase the productivity and inform the future scale-up of the novel reactor. The investigated design parameters are the gap size (d) between the reactor cylinders, the rotational speed (Ω) of the inner cylinder, the flow rate of the reagent (V˙), and the dynamic viscosity of the mixture (μ). For all the investigated cases, the results show that the temporal evolution of the Meff increases and then becomes steady after a maximum level is reached. The point of the maximum Meff is called the equilibration time. It is revealed that the Meff is mainly affected by the flow rate increase as it contracts the Taylor vortices and consequently the mixing deteriorates. Full article
(This article belongs to the Section Mathematical and Computational Fluid Mechanics)
►▼ Show Figures

Figure 1

15 pages, 5104 KB  
Article
Investigation of the Mass Transfer Ratio in a Bubble Column Operated with Various Organic Liquids and Mixtures Under Ambient Conditions
by Stoyan Nedeltchev
Fluids 2026, 11(2), 44; https://doi.org/10.3390/fluids11020044 - 4 Feb 2026
Viewed by 490
Abstract
In this work, for the first time, the dependence of the mass transfer (MT) ratio (kLa coefficient to overall gas holdup) as a function of the superficial gas velocity UG in seven organic liquids was studied. The volumetric liquid-phase [...] Read more.
In this work, for the first time, the dependence of the mass transfer (MT) ratio (kLa coefficient to overall gas holdup) as a function of the superficial gas velocity UG in seven organic liquids was studied. The volumetric liquid-phase MT coefficients kLa were recorded (by means of a polarographic oxygen electrode) in a bubble column (0.095 m in ID) equipped with a single tube (∅3.0 mm in ID) as a gas sparger. It was found that the MT ratio decreases monotonically through all main flow regimes. Both the constant and the exponent of the empirical correlation between the MT ratio and UG were analyzed, and it was found that they depended in a complicated fashion on the Schmidt number, Sc. In three different regions of the Sc number, potential new correlations were discussed. The main conclusion from this work is that the MT ratio is not constant in the heterogeneous regime as reported previously by other researchers. In the case of four binary mixtures between benzene and cyclohexane, it was also found that the MT ratio decreased monotonically as a function of the superficial gas velocity, UG. The effects of both liquid viscosity and surface tension on the MT ratio were also investigated. Full article
(This article belongs to the Special Issue Mass Transfer in Multiphase Reactors)
►▼ Show Figures

Figure 1

35 pages, 10631 KB  
Article
Advancing CFD Simulations Through Machine-Learning-Enabled Mesh Refinement Analysis
by Charles Patrick Bounds and Mesbah Uddin
Fluids 2026, 11(2), 43; https://doi.org/10.3390/fluids11020043 - 30 Jan 2026
Viewed by 832
Abstract
As computational fluid dynamics (CFD) has become more mainstream in production engineering workflows, new demands have been introduced that require high-quality meshes to accurately capture the complex geometries. This evolution has created the need for mesh generation frameworks that help engineers design optimized [...] Read more.
As computational fluid dynamics (CFD) has become more mainstream in production engineering workflows, new demands have been introduced that require high-quality meshes to accurately capture the complex geometries. This evolution has created the need for mesh generation frameworks that help engineers design optimized meshing structures for each new geometry. However, many simulation workflows rely on the experience and intuition of senior engineers rather than systematic frameworks. In this paper, a novel technique for determining mesh convergence is created using machine learning (ML). This method seeks to provide process engineers with a visual feedback mechanism of flow regions that require mesh refinement. The work was accomplished by creating three grid sensitivity studies on various geometries: zero-pressure-gradient flat plate, bump in channel, and axisymmetric free jet. The cases were then simulated using the Reynolds Averaged Navier-Stokes (RANS) models in OpenFOAM (v2306) and had the ML method applied post-hoc using Python (v3.12.6). To apply the method to each case, the flow field was regionalized and clustered using an unsupervised ML model. The ML clustering results were then converted into a similarity score, which compares two grid levels to inform the user whether the region of the flow had converged. To prove this framework, the similarity scores were compared to flow field probes used to determine mesh convergence at key points in the flow. The method was found to be in agreement with the flow field probes on the level of mesh refinement that created convergence. The approach was also seen to provide refinement region recommendations in regions of the flow that align with human intuition of the physics of the flow. Full article
(This article belongs to the Special Issue Machine Learning and Artificial Intelligence in Fluid Mechanics, 2nd Edition)
►▼ Show Figures

Figure 1

25 pages, 8004 KB  
Article
Effects of Discharge and Tailwater Depth on Local Scour of Multi-Grain Beds by Circular Wall Jets
by Amir H. Azimi and Homero Hernandez
Fluids 2026, 11(2), 42; https://doi.org/10.3390/fluids11020042 - 30 Jan 2026
Viewed by 388
Abstract
The scour process of sand particles and multi-grain size and density particles were studied to investigate the segregation process of different particles in a confined channel. The effects of jet intensity and submergence as two controlling parameters were studied, and scour characteristics and [...] Read more.
The scour process of sand particles and multi-grain size and density particles were studied to investigate the segregation process of different particles in a confined channel. The effects of jet intensity and submergence as two controlling parameters were studied, and scour characteristics and profiles were measured. The time history of the scouring process was measured and the results were compared with the scour process in a uniform sand bed as benchmark tests. Experimental data revealed that the eroded area of different particle types increased with the jet intensity, but the erosion of relatively heavier particles was limited due to jet diffusion. The local erosion was affected by the level of submergence and more erosion occurred near the nozzle at low submergence. Increasing the jet Froude number increased the area of deposition, while submergence reduced the overall area of deposition. As submergence increased from 4 to 12, the area of sand particles reduced by more than 50% while the jet intensity was constant. In shallow submergence, increasing jet intensity from 1.46 to 2.11 increased the area of lead balls by 120%, whereas in relatively deep submergence, incrementing jet intensity increased the area of lead balls by more than five times. The effect of flow intensity on variations of scour dimensions was quantified by the densimetric Froude number. While a densimetric Froude number based on mean particle size, D50, was found to be suitable to estimate maximum scour bed in uniform sand beds, experimental data indicated that the best fit is achievable to predict maximum scour depth in multi-grain size and density once D95 is used. Semi-empirical models were proposed to predict scour dimensions as a function of the densimetric Froude number. Full article
(This article belongs to the Topic Advances in Environmental Hydraulics, 2nd Edition)
►▼ Show Figures

Figure 1

17 pages, 5075 KB  
Article
Hydrodynamic Performance and Cavitation Characteristics of an Integrated Pump-Gate
by Yiming Li, Zhengwen Tang, Qiqing Chen, Deyang Liu, Jinxin Zou, David Yang, Xiangrong Luo and Yun Long
Fluids 2026, 11(2), 41; https://doi.org/10.3390/fluids11020041 - 30 Jan 2026
Viewed by 354
Abstract
The integrated pump-gate is a hydraulic facility that integrates a pumping station and a gate, playing a vital role in urban drainage systems, flood control, and other scenarios. Although integrated pump-gates are widely used, their internal flow presents different forms depending on the [...] Read more.
The integrated pump-gate is a hydraulic facility that integrates a pumping station and a gate, playing a vital role in urban drainage systems, flood control, and other scenarios. Although integrated pump-gates are widely used, their internal flow presents different forms depending on the application scenarios, such as backflow, vortices, and cavitation. These effects markedly influence the pump’s hydraulic performance, operational stability, and overall reliability. This study investigates the cavitation characteristics and internal flow fields within the complex geometry of the integrated pump-gate and numerically simulates the cavitation phenomenon using the SST turbulence model. Specifically, the influence of the impeller, guide vanes, and structural supports on the cavitation performance and internal flow state was analyzed. The results show that the geometric characteristics of the impeller’s leading edge significantly influence the cavitation structure. Regarding cavitation performance, NPSHc was determined to be 5.3 m. At the leading edge of the guide vanes, cavitation usually occurs at the axial diffusion position of the flow channel, and the degree of cavitation is affected by the relative position of the guide vanes and the impeller blades. The structural supports and protrusions significantly affect the vortex structures in the flow field, with protrusion-induced vortex clusters dominating the guide vane region. Full article
►▼ Show Figures

Figure 1

24 pages, 11871 KB  
Article
MCV-Driven Effective Viscosity Modulation and Its Hemodynamic Impact in an Idealized Carotid Bifurcation: A Computational Fluid Dynamics Study
by Arif Çutay, Hakan Bayrakcı, Özdeş Çermik and Muharrem İmal
Fluids 2026, 11(2), 40; https://doi.org/10.3390/fluids11020040 - 29 Jan 2026
Viewed by 432
Abstract
Mean corpuscular volume (MCV) is a routinely measured hematological parameter that influences blood viscosity by altering red blood cell volume and packing density. Although MCV is physiologically linked to hemorheological behavior, to the authors’ knowledge, its direct [...] Read more.
Mean corpuscular volume (MCV) is a routinely measured hematological parameter that influences blood viscosity by altering red blood cell volume and packing density. Although MCV is physiologically linked to hemorheological behavior, to the authors’ knowledge, its direct role in modulating large-artery hemodynamics has not been systematically quantified. This study introduces an MCV-driven effective Newtonian viscosity mode to evaluate the first-order impact of MCV variation on carotid bifurcation flow. Rather than employing shear-dependent constitutive laws, blood viscosity was scaled through an MCV-based formulation, yielding three Newtonian fluids corresponding to clinically relevant MCV levels of 70, 90, and 110 fL. Pulsatile CFD simulations were performed in four idealized carotid bifurcation geometries (40°, 50°, 65°, and 100°) to assess the combined influence of vascular geometry and MCV-dependent viscosity variation. Hemodynamic indices including time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), and relative residence time (RRT) were quantified, and a two-way analysis of variance (ANOVA) was employed to distinguish the relative contributions of geometric configuration and MCV. Across the investigated MCV range, increasing MCV produced a geometry-dependent modulation of shear-based indices, with TAWSS increasing by up to approximately 11%, while OSI and RRT decreased by about 20–25% and 10%, respectively, particularly in geometries exhibiting pronounced flow separation. Although vascular geometry remained the dominant determinant of overall hemodynamic patterns, MCV-induced viscosity scaling significantly modulated low-shear and recirculation regions. These findings suggest that MCV-dependent viscosity scaling can complement patient-specific hemodynamic assessments and provide a rational baseline for future shear-dependent and personalized rheological modeling frameworks. Full article
(This article belongs to the Special Issue Advances in Computational Mechanics of Non-Newtonian Fluids, 2nd Edition)
►▼ Show Figures

Figure 1

29 pages, 24358 KB  
Article
Study on Fluid–Structure Interaction Characteristics of Reed Valves in a Reciprocating Refrigeration Compressor
by Ying Zhao, Tao Wang, He Xu, Qixiang Zheng and Fengyu Fan
Fluids 2026, 11(2), 39; https://doi.org/10.3390/fluids11020039 - 29 Jan 2026
Viewed by 611
Abstract
The suction and discharge reed valves are critical components of reciprocating refrigeration compressors, as their dynamic behavior strongly affects the compressor performance. This study investigates the interaction mechanism between unsteady flow characteristics and valve dynamics in a reciprocating refrigeration compressor. A 3D fluid–structure [...] Read more.
The suction and discharge reed valves are critical components of reciprocating refrigeration compressors, as their dynamic behavior strongly affects the compressor performance. This study investigates the interaction mechanism between unsteady flow characteristics and valve dynamics in a reciprocating refrigeration compressor. A 3D fluid–structure interaction (FSI) simulation model was developed, and its reliability was validated by comparing the simulated in-cylinder pressure and suction valve lift with the corresponding experimental measurements. The validated model was subsequently utilized to analyze the evolution of unsteady flow characteristics and valve deformations. Furthermore, a series of FSI simulations was performed to examine the influence of suction pressure, rotational speed, clearance volume ratio, suction valve plate thickness, and discharge valve plate thickness on valve dynamics and compressor performance. The results indicated that suction pressure, rotational speed, and clearance volume ratio all exerted a significant influence on the dynamics of both the suction and discharge valves. Variations in suction valve plate thickness exhibited a minor influence on the dynamic behavior and flow resistance of the discharge valve, whereas adjustments to discharge valve plate thickness had almost no impact on those of the suction valve. This weak coupling characteristic provides flexibility for the independent optimization of the suction and discharge reed valves. The findings of this study lay a solid foundation for optimizing valve design and improving compressor performance. Full article
(This article belongs to the Section Mathematical and Computational Fluid Mechanics)
►▼ Show Figures

Figure 1

11 pages, 5975 KB  
Article
Rheological Characterization of Cerebrospinal Fluid Under Different Temperature Conditions
by Thessa-Carina Bauer, Elke Bradt, Sabine Hild, Andreas Gruber, Tobias Rossmann, Francisco Ruiz-Navarro, Johannes Oberndorfer, Harald Stefanits and Milan Kracalik
Fluids 2026, 11(2), 38; https://doi.org/10.3390/fluids11020038 - 28 Jan 2026
Viewed by 493
Abstract
The flow behavior of fluids can be characterized by rheology and is especially used in the field of polymeric materials. This study focused on characterizing cerebrospinal fluid (CSF) of patients who developed hydrocephalus after subarachnoid hemorrhage (SAH) with rheology. Samples were drawn from [...] Read more.
The flow behavior of fluids can be characterized by rheology and is especially used in the field of polymeric materials. This study focused on characterizing cerebrospinal fluid (CSF) of patients who developed hydrocephalus after subarachnoid hemorrhage (SAH) with rheology. Samples were drawn from an external ventricular drainage (EVD) at four pre-defined time points after the initial hemorrhage. The CSF samples were analyzed using a rotational rheometer with a double gap geometry. In addition to the characterization of viscoelastic parameters, the cumulative storage factor was calculated to determine the interactions in the fluid. In order to investigate the temperature dependence of the CSF properties, the oscillatory measurements were implemented at certain temperatures that simulated specific conditions, such as 5 °C, at which temperature the CSF samples were stored; 35 °C for hypothermic conditions; 37 °C for physiologic conditions; and 40 °C for elevated body temperature. The overall goal was to evaluate whether rheology-based parameters may help in the prediction of shunt dependence for post-hemorrhagic hydrocephalus patients. For this aim, rheological parameters were correlated to certain laboratory parameters, such as erythrocyte and leukocyte count, glucose, lactate, and total protein concentration. Full article
(This article belongs to the Section Non-Newtonian and Complex Fluids)
►▼ Show Figures

Figure 1

8 pages, 188 KB  
Editorial
Advances in Pipe and Channel Flow Modeling
by Kamil Urbanowicz
Fluids 2026, 11(2), 37; https://doi.org/10.3390/fluids11020037 - 28 Jan 2026
Viewed by 381
Abstract
The fluid flow within confined conduits (pipes and channels) remains a cornerstone of hydraulic engineering, underpinning the design, analysis and safe operation of countless industrial, environmental and infrastructural systems [...] Full article
(This article belongs to the Special Issue Modelling Flows in Pipes and Channels)
19 pages, 6272 KB  
Article
Numerical Study on the Aerodynamic Performance and Noise of Composite Bionic Airfoils
by Shunlong Su, Shenwei Xin, Xuemin Ye and Chunxi Li
Fluids 2026, 11(2), 36; https://doi.org/10.3390/fluids11020036 - 28 Jan 2026
Cited by 1 | Viewed by 415
Abstract
Bionic airfoils are an effective method to improve aerodynamic performance and reduce the noise of wind turbine blades. To explore the impact of the lower surface of bird wing airfoils on the aerodynamic performance and noise of blades, this study combines the upper [...] Read more.
Bionic airfoils are an effective method to improve aerodynamic performance and reduce the noise of wind turbine blades. To explore the impact of the lower surface of bird wing airfoils on the aerodynamic performance and noise of blades, this study combines the upper surface of the NACA0018 airfoil with the lower surfaces of the teal, long-eared owl, and sparrowhawk (CBA-T, CBA-O, CBA-S) to create three new composite bionic airfoils (CBAs). The aerodynamic performance of these airfoils is evaluated, and the CBA-O airfoil is identified as having the best aerodynamic characteristics. A comparison of the noise and vortex structures of the CBA-O, owl wing airfoil, and NACA0018 is conducted, and the mechanisms behind the CBA-O airfoil performance improvement and noise reduction are explored. The results indicate that the CBAs enhance the aerodynamic performance of the airfoils. Before stall, the aerodynamic performance of the CBA-O improves the lift-to-drag ratio by 12.7% and 119.7% compared to the owl and NACA0018 airfoils, with its average SPL significantly lower than that of the NACA0018. The CBA-O has smaller vortex sizes at the trailing-edge, and the wake vortex develops more stably, effectively reducing both surface radiation noise and wake noise. Full article
(This article belongs to the Special Issue 10th Anniversary of Fluids—Recent Advances in Fluid Mechanics)
►▼ Show Figures

Figure 1

24 pages, 5259 KB  
Article
Design Methodology and Experimental Verification of a Novel Orifice Plate Rectifier
by Zhe Li, Guixiang Lu, Yan Li, Yanhua Lai, Zhen Dong and Mingxin Lyu
Fluids 2026, 11(2), 35; https://doi.org/10.3390/fluids11020035 - 28 Jan 2026
Viewed by 799
Abstract
Optimizing the rectification and pressure loss controlled by the aperture structure is challenging, with particular attention paid to the problem of precisely modeling the rectification process of multilayer wire mesh in pulse tube cryocoolers. This work offers a rectifier design method based on [...] Read more.
Optimizing the rectification and pressure loss controlled by the aperture structure is challenging, with particular attention paid to the problem of precisely modeling the rectification process of multilayer wire mesh in pulse tube cryocoolers. This work offers a rectifier design method based on the regularized orifice plate. A novel rectifier that reduces flow resistance and shows rectification performance comparable to a woven wire mesh is created by analyzing its effects on the flow using numerical simulation. Flow uniformity and pressure loss are selected as evaluation metrics. Point flow velocity calibration is performed under fully developed flow conditions to derive a quantitative equation relating voltage to flow velocity. A multi-cross-section radial flow velocity distribution test platform is set up. The experimental results show that the uniformity of woven wire mesh reaches 0.9670 under low-flow conditions and 0.9629 for the novel eight-ring rectifier, but the pressure drop reduction reaches 57.64%; the uniformity of the novel eight-ring rectifier is improved by 0.91~1.94% compared to that of woven wire mesh under high-flow conditions, and the pressure drop is reduced by 87.74~89.09%. The rectifier features uniformly distributed apertures, facilitating modeling and machining. Full article
(This article belongs to the Section Heat and Mass Transfer)
►▼ Show Figures

Figure 1

24 pages, 5941 KB  
Article
A Fully Implicit Model of Compressible Capillary Flows
by Jean-Paul Caltagirone
Fluids 2026, 11(2), 34; https://doi.org/10.3390/fluids11020034 - 27 Jan 2026
Viewed by 450
Abstract
Small-scale two-phase flows are subject to intense capillary accelerations that must be treated with care in order to avoid artifacts often associated with the numerical methodologies used, such as excessive fragmentation of structures. This analysis proposes a formulation of capillary actions for compressible [...] Read more.
Small-scale two-phase flows are subject to intense capillary accelerations that must be treated with care in order to avoid artifacts often associated with the numerical methodologies used, such as excessive fragmentation of structures. This analysis proposes a formulation of capillary actions for compressible viscous two-phase flows within the framework of discrete mechanics, where the concept of mass is abandoned in favor of a law of motion that describes the conservation of accelerations, one related to inertia and the other to external actions. With the introduction of the capillary term, the sum of a capillary potential gradient and the dual curl of a vector potential is consistent with the other terms of the law of motion, a formal Helmholtz–Hodge decomposition. This fully compressible formulation reproduces the capillary waves generated by the source terms and the contact and shock discontinuities in the two immiscible fluids. This methodology completely eliminates parasitic currents due mainly to the presence of residual curl in the capillary source terms. Several classic examples demonstrate the validity of this approach. Full article
(This article belongs to the Special Issue Multiphase Simulations with the Volume-of-Fluid (VOF) Approach)
►▼ Show Figures

Figure 1

21 pages, 4251 KB  
Article
Comparative Analysis of Unsteady Natural Convection and Thermal Performance in Rectangular and Square Cavities Filled with Stratified Air
by Syed Mehedi Hassan Shaon, Md. Mahafujur Rahaman, Suvash C. Saha and Sidhartha Bhowmick
Fluids 2026, 11(2), 33; https://doi.org/10.3390/fluids11020033 - 27 Jan 2026
Cited by 1 | Viewed by 486
Abstract
A comprehensive numerical analysis has been conducted to investigate unsteady natural convection (UNC), bifurcation behavior, and heat transfer (HT) in a rectangular enclosure containing thermally stratified air. The enclosure comprises a uniformly heated bottom wall, thermally stratified vertical sidewalls, and a cooled top [...] Read more.
A comprehensive numerical analysis has been conducted to investigate unsteady natural convection (UNC), bifurcation behavior, and heat transfer (HT) in a rectangular enclosure containing thermally stratified air. The enclosure comprises a uniformly heated bottom wall, thermally stratified vertical sidewalls, and a cooled top wall. To assess thermal performance, square and rectangular cavities with identical boundary conditions and working fluid are considered. The finite volume method (FVM) is used to solve the governing equations over a wide range of Rayleigh numbers (Ra = 101 to 109) for air with a Prandtl number (Pr) of 0.71. Flow dynamics and thermal performance are analyzed using temperature time series (TTS), limit point–limit cycle behavior, average Nusselt number (Nuavg), average entropy generation (Savg), average Bejan number (Beavg), and the ecological coefficient of performance (ECOP). In the rectangular cavity, the transition from steady to chaotic flow exhibits three bifurcations: a pitchfork bifurcation at Ra = 3 × 104–4 × 104, a Hopf bifurcation at Ra = 3 × 106–4 × 106, and the onset of chaotic flow at Ra = 9 × 107–2 × 108. The comparative analysis indicates that Nuavg remains nearly identical for both cavities within Ra = 105 to 107. However, at Ra = 108, the HT rate in the rectangular cavity is 29.84% higher than that of the square cavity, while Savg and Beavg differ by 39.32% and 37.50%, respectively. Despite higher HT and Savg in the rectangular enclosure, the square cavity demonstrates superior overall thermal performance by 13.52% at Ra = 108. These results offer significant insights for optimizing cavity geometries in thermal system design based on energy efficiency and entropy considerations. Full article
(This article belongs to the Special Issue Convective Flows and Heat Transfer)
►▼ Show Figures

Figure 1

3 pages, 143 KB  
Editorial
Editorial: Rarefied Gas Flows—From Micro–Nano Scale to the Hypersonic Regime
by Ehsan Roohi
Fluids 2026, 11(2), 32; https://doi.org/10.3390/fluids11020032 - 26 Jan 2026
Viewed by 437
Abstract
Rarefied gas dynamics spans a wide spectrum of applications: micro–nano devices where the mean free path becomes comparable to characteristic lengths, vacuum and porous systems where Knudsen diffusion emerges, and high-speed (including hypersonic) flows where non-equilibrium effects shape transport and surface interactions [...] [...] Read more.
Rarefied gas dynamics spans a wide spectrum of applications: micro–nano devices where the mean free path becomes comparable to characteristic lengths, vacuum and porous systems where Knudsen diffusion emerges, and high-speed (including hypersonic) flows where non-equilibrium effects shape transport and surface interactions [...] Full article
(This article belongs to the Special Issue Rarefied Gas Flows: From Micro-Nano Scale to Hypersonic Regime)
17 pages, 10638 KB  
Article
Numerical Investigation of Noise Generation from a Variable-Pitch Propeller at Various Flight Conditions
by Mateus Grassano Lattari, Victor Henrique Pereira da Rosa, Filipe Dutra da Silva and César José Deschamps
Fluids 2026, 11(2), 31; https://doi.org/10.3390/fluids11020031 - 26 Jan 2026
Viewed by 586
Abstract
The advent of electric propulsion for new aircraft designs necessitates the optimization of propeller aerodynamic performance and the reduction of acoustic signatures. Variable-pitch propellers present a promising solution, offering the flexibility to adjust blade angles in response to different flight conditions. The study [...] Read more.
The advent of electric propulsion for new aircraft designs necessitates the optimization of propeller aerodynamic performance and the reduction of acoustic signatures. Variable-pitch propellers present a promising solution, offering the flexibility to adjust blade angles in response to different flight conditions. The study investigates the performance of blade pitch configurations tailored to specific flight conditions. Rather than a dynamic pitch change, the research evaluates discrete pitch settings coupled with corresponding advance ratios to identify optimal operating points. Findings show that increasing collective pitch in response to a higher advance ratio (forward flight) successfully maintains aerodynamic efficiency and thrust, with an expected increase in torque. While this adjustment leads to an anticipated rise in noise due to higher aerodynamic loading, results reveal that a collective pitch increment of +5° actively suppresses broadband noise at frequencies above 2 kHz. Analysis of the flow field and surface pressure fluctuations indicates this suppression is directly attributed to the mitigation of outboard propeller stall. Ultimately, this work demonstrates the feasibility of using collective pitch adjustments not only to enhance flight performance but also to actively control and suppress components of the propeller noise signature, such as the broadband noise. Full article
(This article belongs to the Section Mathematical and Computational Fluid Mechanics)
►▼ Show Figures

Figure 1

16 pages, 1117 KB  
Article
Algebraic Prediction of Pressure and Lift for High-Angle-of-Attack Supersonic Asymmetric Delta Wings Based on Geometric Similarity
by Xue-Ying Wang, Jie Peng and Zi-Niu Wu
Fluids 2026, 11(2), 30; https://doi.org/10.3390/fluids11020030 - 24 Jan 2026
Viewed by 381
Abstract
In this paper, we explore the feasibility of deriving a simple, physically meaningful, and compact formulation for the pressure distribution and lift of an asymmetric delta wing at high angles of attack with an attached shock wave. Such a model would be valuable [...] Read more.
In this paper, we explore the feasibility of deriving a simple, physically meaningful, and compact formulation for the pressure distribution and lift of an asymmetric delta wing at high angles of attack with an attached shock wave. Such a model would be valuable for rapid engineering analysis. Our approach begins with a compact pressure approximation in the linear regime, which is then extended to the nonlinear case through a geometric transformation and the assumption of functional similarity between linear and nonlinear solutions. This method bridges the solution in the central nonuniform flow region to the exact solutions in the uniform flow regions near the leading-edge shock waves, in a manner analogous to methods used for supersonic starting flow. The model is shown to reproduce existing results for both symmetric and yawed delta wings within an acceptable error margin, providing a compact explicit expression for the normal force coefficient as a weighted average of pressure coefficients from the two uniform flow regions. Additionally, we outline how the approach may be extended to the upper surface, where the uniform flow is described by swept Prandtl–Meyer relations. Full article
(This article belongs to the Special Issue High-Speed Processes in Continuous Media)
►▼ Show Figures

Figure 1

Show export options expand_more Show export options expand_less
Select all
Export citation of selected articles as:
 
Displaying articles 1-31
Previous Issue
Next Issue
Back to TopTop