Fluids

14 pages, 5218 KB

Open AccessArticle

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

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)

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27 pages, 5791 KB

Open AccessArticle

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

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)

31 pages, 13341 KB

Open AccessArticle

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

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

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27 pages, 5645 KB

Open AccessArticle

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

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)

20 pages, 7392 KB

Open AccessArticle

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

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)

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30 pages, 2478 KB

Open AccessArticle

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

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)

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18 pages, 2616 KB

Open AccessArticle

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

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)

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19 pages, 5586 KB

Open AccessArticle

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

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)

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21 pages, 6633 KB

Open AccessArticle

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

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)

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21 pages, 1543 KB

Open AccessArticle

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

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)

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22 pages, 6448 KB

Open AccessArticle

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

Abstract

The drag wake of a dimpled sphere is studied experimentally using stereo particle image velocimetry at a Reynolds number of

10^{5}

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

10^{5}

in both unstratified and stratified (Froude number

≃ 80

) fluids at downstream distances of

2 \leq x / D \leq 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)

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21 pages, 5290 KB

Open AccessArticle

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

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 (M_eff) 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 (M_eff) 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 (

\dot{V}

), and the dynamic viscosity of the mixture (μ). For all the investigated cases, the results show that the temporal evolution of the M_eff increases and then becomes steady after a maximum level is reached. The point of the maximum M_eff is called the equilibration time. It is revealed that the M_eff 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)

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15 pages, 5104 KB

Open AccessArticle

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

Abstract

In this work, for the first time, the dependence of the mass transfer (MT) ratio (k_La coefficient to overall gas holdup) as a function of the superficial gas velocity U_G 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 (k_La coefficient to overall gas holdup) as a function of the superficial gas velocity U_G in seven organic liquids was studied. The volumetric liquid-phase MT coefficients k_La 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 U_G 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, U_G. 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)

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35 pages, 10631 KB

Open AccessArticle

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

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)

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25 pages, 8004 KB

Open AccessArticle

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

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)

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17 pages, 5075 KB

Open AccessArticle

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

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, NPSH_c 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

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24 pages, 11871 KB

Open AccessArticle

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

Abstract

Mean corpuscular volume (

M C V

) is a routinely measured hematological parameter that influences blood viscosity by altering red blood cell volume and packing density. Although

M C V

is physiologically linked to hemorheological behavior, to the authors’ knowledge, its direct [...] Read more.

Mean corpuscular volume (

M C V

) is a routinely measured hematological parameter that influences blood viscosity by altering red blood cell volume and packing density. Although

M C V

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

M C V

-driven effective Newtonian viscosity mode to evaluate the first-order impact of

M C V

variation on carotid bifurcation flow. Rather than employing shear-dependent constitutive laws, blood viscosity was scaled through an

M C V

-based formulation, yielding three Newtonian fluids corresponding to clinically relevant

M C V

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

M C V

-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

M C V

. Across the investigated

M C V

range, increasing

M C V

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,

M C V

-induced viscosity scaling significantly modulated low-shear and recirculation regions. These findings suggest that

M C V

-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)

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29 pages, 24358 KB

Open AccessArticle

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

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)

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11 pages, 5975 KB

Open AccessArticle

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

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)

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