Fluids

8 pages, 174 KiB

Open AccessEditorial

Recent Advances in Fluid Mechanics: Feature Papers, 2024

by Giuliano De Stefano and D. Andrew S. Rees

Fluids 2025, 10(5), 137; https://doi.org/10.3390/fluids10050137 - 20 May 2025

The present Special Issue consists of a collection of feature articles by distinct investigators and research groups discussing new findings or cutting-edge developments concerning different aspects of fluid mechanics [...] Full article

(This article belongs to the Special Issue Recent Advances in Fluid Mechanics: Feature Papers, 2024)

30 pages, 7346 KiB

Open AccessArticle

Numerical Analysis of Submerged Horizontal Plate Wave Energy Converter Device Considering Float Effects

by Rodrigo Costa Batista, Marla Rodrigues de Oliveira, Elizaldo Domingues dos Santos, Luiz Alberto Oliveira Rocha, Liércio André Isoldi and Mateus das Neves Gomes

Fluids 2025, 10(5), 136; https://doi.org/10.3390/fluids10050136 - 19 May 2025

Abstract

This study proposes a three-dimensional numerical wave tank (NWT) to calculate wave propagation and hydrodynamic forces based on the Navier–Stokes equation, using commercial Computational Fluid Dynamic (CFD) software ANSYS Fluent. The VOF Method is utilized to identify the free surface. The CFD model [...] Read more.

This study proposes a three-dimensional numerical wave tank (NWT) to calculate wave propagation and hydrodynamic forces based on the Navier–Stokes equation, using commercial Computational Fluid Dynamic (CFD) software ANSYS Fluent. The VOF Method is utilized to identify the free surface. The CFD model employed for generating waves in the NWT is initially verified using analytical theory to evaluate the accuracy of the results. In addition, the User-Defined Function (UDF) in ANSYS Fluent is implemented to ensure the model performs under the oscillatory conditions of the Submerged Horizontal Plate (SHP) Wave Energy Converter (WEC) device, which is localized at the center of the NWT. Finally, the influence of SHP oscillation on the device’s average efficiency was analyzed by comparing seven cases with different geometric configurations, considering both the oscillating and non-oscillating conditions of the SHP under the incidence of different waves. The results indicated that the geometric configuration and wave conditions of Case 4 achieved the best performance, reaching an average efficiency of 35.68%. Full article

(This article belongs to the Section Mathematical and Computational Fluid Mechanics)

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15 pages, 6185 KiB

Open AccessArticle

Investigating Moisture-Induced Particle Behavior in a Horizontal Shaft Mixer

by Minkyung Sim and Kwang Kim

Fluids 2025, 10(5), 135; https://doi.org/10.3390/fluids10050135 - 19 May 2025

Abstract

Grains stored in silos and pellets for injection molding deteriorate in quality due to increased moisture in the particles when exposed to air for a long period of time, so it is necessary to reduce the moisture in the particles through the mixing [...] Read more.

Grains stored in silos and pellets for injection molding deteriorate in quality due to increased moisture in the particles when exposed to air for a long period of time, so it is necessary to reduce the moisture in the particles through the mixing process. However, few studies have conducted parallel experiments and simulations to understand the behavior of particles depending on their moisture content. In this study, mixing experiments were conducted using superabsorbent polymer (SAP) beads that expand depending on the moisture content, and the interparticle friction coefficient and interface friction coefficient required for simulation were derived. As a result, it was found that moisture generates an adhesive force that causes interparticle cohesion, and as the moisture content increases further, the particles adhere to the vessel wall due to the adhesive force. In addition, particles with high moisture content (e.g., 90%) showed faster mixing behavior similar to dry particles, as indicated by the Lacey Mixing Index (LMI), while low moisture particles (e.g., 60%) showed the slowest mixing. It is expected that the mixing characteristics of particles depending on the moisture content can be understood and will be useful for the design of horizontal shaft mixers. Full article

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46 pages, 18159 KiB

Open AccessReview

Recent Developments in the Immersed Boundary Method for Complex Fluid–Structure Interactions: A Review

by Omkar Powar, Pedapudi Anantha Hari Arun, Anwak Manoj Kumar, Mithun Kanchan, B. M. Karthik, Poornesh Mangalore and Mohith Santhya

Fluids 2025, 10(5), 134; https://doi.org/10.3390/fluids10050134 - 16 May 2025

Abstract

The “immersed boundary method (IBM)” is considered to be the most efficacious and versatile technique to solve flow problems associated with intricate geometries. The first part of this review examines recent advancements in IBM, essential for the simulation of “fluid–structure interactions (FSIs)” in [...] Read more.

The “immersed boundary method (IBM)” is considered to be the most efficacious and versatile technique to solve flow problems associated with intricate geometries. The first part of this review examines recent advancements in IBM, essential for the simulation of “fluid–structure interactions (FSIs)” in sophisticated systems. This review highlights significant developments in turbulence modeling, adaptive mesh refinement, and complex geometric simulations, demonstrating IB methods’ capacity to seamlessly integrate arbitrary geometries into structured computational grids while preserving computational efficiency. Various IB techniques are analyzed for enforcing boundary conditions on dynamic immersed boundaries, with notable breakthroughs in managing velocity discontinuities, spurious oscillations, and large-scale deformations. Recent findings illustrate the versatility of IB methods, with applications encompassing biological fluid dynamics, turbulent multiphase flows, and cavitating flows. These innovations not only enhance computational performance but also address evolving challenges across engineering and scientific fields, establishing IB methods as a robust tool for resolving complex, multidisciplinary problems with high accuracy and efficiency. Full article

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40 pages, 3557 KiB

Open AccessArticle

Modified Semi-Lagrangian Godunov-Type Method Without Numerical Viscosity for Shocks

by Valeriy Nikonov

Fluids 2025, 10(5), 133; https://doi.org/10.3390/fluids10050133 - 16 May 2025

Abstract

Most high-order Euler-type methods have been proposed to solve one-dimensional scalar hyperbolic conservational law. These methods resolve smooth variations in flow parameters accurately and simultaneously identify the discontinuities. A disadvantage of Euler-type methods is the parameter change stretching in the shock over a [...] Read more.

Most high-order Euler-type methods have been proposed to solve one-dimensional scalar hyperbolic conservational law. These methods resolve smooth variations in flow parameters accurately and simultaneously identify the discontinuities. A disadvantage of Euler-type methods is the parameter change stretching in the shock over a few mesh cells. In reality, in the shock, the flow properties change abruptly at once for the computational mesh. In our considerations, the mean free path of a flow particle is much smaller than the mesh cell size. This paper describes a modification of the semi-Lagrangian Godunov-type method, which was proposed by the author in the previously published paper. The modified method also does not have numerical viscosity for shocks. In the previous article, a linear law for the distribution of flow parameters was employed for a rarefaction wave when modeling the Shu-Osher problem with the aim of reducing parasitic oscillations. Additionally, the nonlinear law derived from the Riemann invariants was used for the remaining test problems. This article proposes an advanced method, namely, a unified formula for the density distribution of rarefaction waves and modification of the scheme for modeling moderately strong shock waves. The obtained results of numerical analysis, including the standard problem of Sod, the Riemann problem of Lax, the Shu–Osher shock-tube problem and a few author’s test cases are compared with the exact solution, the data of the previous method and the Total Variation Deminishing (TVD) scheme results. This article delineates the further advancement of the numerical scheme of the proposed method, specifically presenting a unified mathematical formulation for an expanded set of test problems. Full article

38 pages, 22598 KiB

Open AccessArticle

Assessing the Effect of Air Ventilation on the Dispersion of Exhaled Aerosol Particles in a Lecture Hall: Simulation Strategy and Streamlined Workflow

by Arnav Ajmani, Lars Kirchhof, Alireza Rouhi and Carsten Mehring

Fluids 2025, 10(5), 132; https://doi.org/10.3390/fluids10050132 - 15 May 2025

Abstract

An efficient solution strategy based on fluid network modeling, computational fluid dynamics (CFD) and discrete particle modeling (DPM) is presented in order to predict and improve air quality, specifically regarding breathing aerosol concentration, in a person-occupied mechanically ventilated room. The efficiency of the [...] Read more.

An efficient solution strategy based on fluid network modeling, computational fluid dynamics (CFD) and discrete particle modeling (DPM) is presented in order to predict and improve air quality, specifically regarding breathing aerosol concentration, in a person-occupied mechanically ventilated room. The efficiency of the proposed workflow is evaluated for the specific case of a lecture hall. It is found that the actual vent system is imbalanced and inefficient in managing the aerosol concentration within the room. Despite a high volumetric exchange rate, aerosol residence times and local aerosol concentrations remain high over an extended period of time, without additional efforts to alter air flow circulation throughout the room. The proposed strategy illustrates how such changes can be efficiently implemented in the basic 1D/3D co-simulation workflow. Analysis of the lecture hall and vent system shows that the execution time for the overall process workflow can be optimized by the following: (1) CAD geometry generation of the room via 3D laser scanning, (2) mesh generation based on the anticipated air discharge behavior from the vent system and (3) by employing HPC resources. Additional simplifications such as the decoupling of vent air flow and room aerodynamics, as observed for the investigated test case, one-way coupling between air flow and aerosol dispersion at low aerosol concentrations and the successive solution of flow field equations can further reduce the problem’s complexity and processing times. Full article

(This article belongs to the Special Issue Industrial CFD and Fluid Modelling in Engineering, 2nd Edition)

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22 pages, 11898 KiB

Open AccessArticle

Impact of Viscous Droplets on Dry and Wet Substrates for Spray Painting Processes

by Qiaoyan Ye, Oliver Tiedje, Bo Shen and Joachim Domnick

Fluids 2025, 10(5), 131; https://doi.org/10.3390/fluids10050131 - 15 May 2025

Abstract

This paper presents numerical studies of the viscous droplet impact on dry and wetted solid walls for spray painting applications, focusing on air entrapment, film structure, and flake (flat pigment) orientation. The results were compared with experimental observations using various high-speed camera arrangements. [...] Read more.

This paper presents numerical studies of the viscous droplet impact on dry and wetted solid walls for spray painting applications, focusing on air entrapment, film structure, and flake (flat pigment) orientation. The results were compared with experimental observations using various high-speed camera arrangements. For paint droplet impact on dry substrates, a dynamic contact angle model was developed and used in numerical simulations. This contact angle model was verified with experimental observations. For the droplet impact on wet surfaces, characteristic crater sizes (diameter and depth) were defined considering also the effect of the film thickness. A strong correlation with the droplet impact Reynolds number was observed. In addition, a user-defined 6DOF (6-degrees-of-freedom) solver was implemented in a CFD program to perform calculations of rigid body motions within the impacting droplet, technically relevant for the resulting effect of flakes in metallic effect paints. The developed models were applied in parameter studies to further clarify the existing dependencies on application and fluid parameters more quantitatively. The simulation results are helpful to understand and to improve painting processes with respect to the final quality parameters. Full article

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

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16 pages, 2119 KiB

Open AccessArticle

Steady Particulate Taylor-Couette Flow with Particle Migration

by C. Q. Ru

Fluids 2025, 10(5), 130; https://doi.org/10.3390/fluids10050130 - 14 May 2025

Abstract

Steady Taylor-Couette flow of a particle-fluid suspension with non-neutrally buoyant particles between two coaxial rotating cylinders is studied with a novel two-fluid model. It is shown that steady particle distribution in particulate Taylor-Couette flow can exist in the case when the solid walls [...] Read more.

Steady Taylor-Couette flow of a particle-fluid suspension with non-neutrally buoyant particles between two coaxial rotating cylinders is studied with a novel two-fluid model. It is shown that steady particle distribution in particulate Taylor-Couette flow can exist in the case when the solid walls are permeable where the particles and the fluid can be sucked or injected with equal but opposite normal fluxes. With this assumption, an explicit formula is derived for the axisymmetric steady radial distribution of particles with particle migration in the dilute limit. Detailed results for several cases of major interest show that the local rate of particle migration depends largely on the local azimuthal speed, and the steady volume fraction of particles typically attains its maximum (or minimum) at the location of minimum (or maximum) local azimuthal speed. In particular, with a wider gap between two cylinders and a Stokes number of particles around the order of unity, the non-monotonic radial distribution of particle volume fraction with interior local maximum and/or minimum can occur when the inner cylinder rotates with the outer cylinder fixed or when the two cylinders counter-rotate with equal but opposite angular velocities. Full article

(This article belongs to the Section Flow of Multi-Phase Fluids and Granular Materials)

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41 pages, 15728 KiB

Open AccessReview

A Review of Mesh Adaptation Technology Applied to Computational Fluid Dynamics

by Guglielmo Vivarelli, Ning Qin and Shahrokh Shahpar

Fluids 2025, 10(5), 129; https://doi.org/10.3390/fluids10050129 - 13 May 2025

Abstract

Mesh adaptation techniques can significantly impact Computational Fluid Dynamics by improving solution accuracy and reducing computational costs. In this review, we begin by defining the concept of mesh adaptation, its core components and the terminology commonly used in the community. We then categorise [...] Read more.

Mesh adaptation techniques can significantly impact Computational Fluid Dynamics by improving solution accuracy and reducing computational costs. In this review, we begin by defining the concept of mesh adaptation, its core components and the terminology commonly used in the community. We then categorise and evaluate the main adaptation strategies, focusing both on error estimation and mesh modification techniques. In particular, we analyse the two most prominent families of error estimation: feature-based techniques, which target regions of high physical gradients and goal-oriented adjoint methods, which aim to reduce the error in a specific integral quantity of interest. Feature-based methods are advantageous due to their reduced computational cost: they do not require adjoint solvers, and they have a natural ability to introduce anisotropy. A substantial portion of the literature relies on second-order derivatives of scalar flow quantities to construct sensors that can be equidistributed to minimise discretisation error. However, when used carelessly, these methods can lead to over-refinement, and they are generally outperformed by adjoint-based techniques when improving specific target quantities. Goal-oriented methods typically achieve higher accuracy in fewer adaptation steps with coarser meshes. It will be seen that various approaches have been developed to incorporate anisotropy into adjoint-based adaptation, including hybrid error sensors that combine feature-based and goal-oriented indicators, sequential strategies and adjoint weighting of fluxes. After years of limited progress, recent work has demonstrated promising results, including certifiable solutions and applications to increasingly complex cases such as transonic compressor blades and film-cooled turbines. Despite these advances, several critical challenges remain: efficient parallelisation, robust geometry integration, application to unsteady flows and deployment in high-order discretisation frameworks. Finally, examples of the potential role of artificial intelligence in guiding or accelerating mesh adaptation are also discussed. Full article

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25 pages, 1437 KiB

Open AccessReview

Review of the Color Gradient Lattice Boltzmann Method for Simulating Multi-Phase Flow in Porous Media: Viscosity, Gradient Calculation, and Fluid Acceleration

by Fizza Zahid and Jeffrey A. Cunningham

Fluids 2025, 10(5), 128; https://doi.org/10.3390/fluids10050128 - 13 May 2025

Abstract

The lattice Boltzmann method (LBM) is widely applied to model the pore-scale two-phase flow of immiscible fluids through porous media, and one common variant of the LBM is the color gradient method (CGM). However, in the literature, many competing algorithms have been proposed [...] Read more.

The lattice Boltzmann method (LBM) is widely applied to model the pore-scale two-phase flow of immiscible fluids through porous media, and one common variant of the LBM is the color gradient method (CGM). However, in the literature, many competing algorithms have been proposed for accomplishing different steps in the CGM. Therefore, this paper is the first in a series that aims to critically review and evaluate different algorithms and methodologies that have been proposed for use in the CGM. Specifically, in this paper, we (1) provide a brief introduction to the LBM and CGM that enables and facilitates consideration of more sophisticated topics subsequently; (2) compare three methods for modeling the behavior of fluids of moderately different viscosities; (3) compare two methods for calculating the color gradient; and (4) compare two methods for modeling external forces or accelerations acting upon the fluids of interest. These topics are selected for the first paper in the series because proper selection of these algorithms is necessary and sufficient to perform two common “benchmark” simulations, namely bubble tests and layered Poiseuille flow. Future papers in the series will build upon these topics, considering more challenging conditions or phenomena. By systematically reviewing key aspects, features, capabilities, and limitations of the CGM, this series of papers will extend our collective ability to apply the method to a variety of important fluid flow problems in geosciences and engineering. Full article

(This article belongs to the Special Issue Recent Advances in Fluid Mechanics: Feature Papers, 2024)

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10 pages, 3383 KiB

Open AccessArticle

Droplets at Liquid-Fluid Interfaces: Stages Leading to Coalescence

by Jose Davalos-Monteiro, Qi Liu and J. Carlos Santamarina

Fluids 2025, 10(5), 127; https://doi.org/10.3390/fluids10050127 - 12 May 2025

Abstract

Droplet coalescence at interfaces affects industrial and natural processes. Previous studies focused on droplet stability and thin film drainage. We use meticulous experiments to infer the evolution of coalescence for both ascending and descending droplets under different conditions. Images show the anticipatory deformation [...] Read more.

Droplet coalescence at interfaces affects industrial and natural processes. Previous studies focused on droplet stability and thin film drainage. We use meticulous experiments to infer the evolution of coalescence for both ascending and descending droplets under different conditions. Images show the anticipatory deformation of the interface and dimple formation during the approach phase. While the droplet rests at the interface, the two surfaces interact through the draining thin film, and the effective interfacial tension can be higher than twice the interfacial tension between the two fluids, suggesting not only concurrent action but also potential changes in interfacial tension in thin films. Following the film breakage, the unbalanced force propels the droplet into the continuous phase, i.e., the slingshot effect. Multiple droplets may coexist at the interface and collectively contribute to its deformation, which in turn pushes the droplets together. The various stages of droplet coalescence are influenced by the droplet and host fluid viscosities, densities, interfacial tension, size, and initial interface curvature. Full article

(This article belongs to the Section Flow of Multi-Phase Fluids and Granular Materials)

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12 pages, 5641 KiB

Open AccessArticle

A Numerical Investigation of Sinusoidal Flow in Porous Media with a Simple Cubic Beam Structure at 1 Hz and 100 Hz Under Different Porosity Conditions

by Sin-Mao Chen, Boe-Shong Hong and Shiuh-Hwa Shyu

Fluids 2025, 10(5), 126; https://doi.org/10.3390/fluids10050126 - 12 May 2025

Abstract

This study aims to clarify how porosity and frequency interact to influence permeability and flow behavior in porous media subjected to sinusoidal pressure variations. Specifically, we investigate oscillatory flow at 1 Hz and 100 Hz under varying porosity conditions using a pore-scale Computational [...] Read more.

This study aims to clarify how porosity and frequency interact to influence permeability and flow behavior in porous media subjected to sinusoidal pressure variations. Specifically, we investigate oscillatory flow at 1 Hz and 100 Hz under varying porosity conditions using a pore-scale Computational Fluid Dynamics (CFD) model. The model is validated against the Johnson–Koplik–Dashen (JKD) model to ensure accuracy in capturing dynamic permeability. At 1 Hz, where the oscillation period greatly exceeds the system’s time constant

τ

, the flow reaches a quasi-steady state with dynamic permeability approximating static permeability. Increasing porosity enhances Darcy velocity, with minimal phase difference between velocity and pressure. At 100 Hz, flow behavior depends on the ratio of the oscillation period

T

to

τ

. For high porosity (

φ = 0.840

,

T \approx τ

), the flow does not fully develop before the pressure gradient reverses, leading to significant phase lag. For low porosity (

φ = 0.370

,

T \approx 12 τ

), the phase lag is smaller but remains non-zero due to the smooth temporal variation in pressure. This work contributes to the understanding of porous flow dynamics by revealing how porosity modulates both the amplitude and phase angle of dynamic permeability in frequency-dependent porous flows, providing a framework for predicting phase lag in frequency-sensitive applications. Full article

(This article belongs to the Collection Feature Paper for Mathematical and Computational Fluid Mechanics)

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94 pages, 11117 KiB

Open AccessReview

An Overview of Viscous and Highly Viscous Fluid Flows in Straight and Elbow Pipes: I—Single-Phase Flows

by Leonardo Di G. Sigalotti and Enrique Guzmán

Fluids 2025, 10(5), 125; https://doi.org/10.3390/fluids10050125 - 11 May 2025

Abstract

The flow of viscous and highly viscous fluids in straight and bent pipes and channels is a fundamental process in a wide variety of industrial applications and is, therefore, of great interest in science and engineering. Understanding the physics behind such flows has [...] Read more.

The flow of viscous and highly viscous fluids in straight and bent pipes and channels is a fundamental process in a wide variety of industrial applications and is, therefore, of great interest in science and engineering. Understanding the physics behind such flows has a direct impact on the design of efficient, safe and reliable systems. The type of fluid, which can be viscous or even highly viscous, and the pipe geometry can affect the flow dynamics, the pressure loss and the overall efficiency of the process. In this paper, we provide an extensive review of the state-of-the-art research concerning the flow of Newtonian and non-Newtonian, single-phase fluids in straight and bent pipes. Since a big amount of work in the literature is devoted to the study of Newtonian pipe flows, the paper starts with a brief outline of the nonlinear theory of viscous Newtonian fluid flow in pipes, including a survey of early and recent analytical solutions to the Navier–Stokes equations. The central part of the paper deals with an extensive overview of existing experimental and numerical research work on viscous Newtonian pipe flows. Separate sections are devoted to non-Newtonian fluid flows, the problem of entropy generation due to irreversible processes in the flow and hydromagnetic Newtonian and non-Newtonian pipe flow. The review closes with a brief survey of machine learning and artificial intelligence modeling applied to pipe flow along with future trends and challenges in pipe flow research. Full article

(This article belongs to the Special Issue Pipe Flow: Research and Applications, 2nd Edition)

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16 pages, 6209 KiB

Open AccessArticle

Numerical Simulation of Blood Clot Extraction Process Using Aspiration-Based Mechanical Thrombectomy

by Sreenivas Venguru, Shyam Sunder Yadav, Tanmaya Mahapatra and Sanjay Kumar Kochar

Fluids 2025, 10(5), 124; https://doi.org/10.3390/fluids10050124 - 9 May 2025

Abstract

This paper simulates the blood clot extraction process inside an idealized cylindrical blood vessel model using the aspiration-based thrombectomy technique. A fully Eulerian technique is used within the finite volume method where incompressible Navier–Stokes equations are solved in the fluid region. In contrast, [...] Read more.

This paper simulates the blood clot extraction process inside an idealized cylindrical blood vessel model using the aspiration-based thrombectomy technique. A fully Eulerian technique is used within the finite volume method where incompressible Navier–Stokes equations are solved in the fluid region. In contrast, the Cauchy stress equation is solved in the clot region. Blood is assumed to be a Newtonian fluid, while the clot is either hyperelastic or viscoelastic material. In the hyperelastic formulation, the clot deformation is calculated based on the left Cauchy–Green deformation tensor, while the stresses are based on the linear Mooney–Rivlin model. In the viscoelastic formulation, the Oldroyd B model is used within the log conformation approach to calculate the viscoelastic stresses in the clot. The interface between the blood and the clot is tracked with the help of the geometric volume-of-fluid method. We focus on the role of flow variables like the pressure, velocity, and proximity between the clot and the catheter tip to successfully capture the clot under catheter suction. We observe that, once the clot is attracted to the catheter port due to pressure forces, the viscous stresses try to drag it inside the catheter. On the other hand, if the clot is not initially attracted, it is carried downstream by the viscous stresses. If the suction velocity is low (∼0.2 m/s), the clot cannot be sucked inside the catheter, even if it is touching the catheter. At a higher suction velocity of 0.4 m/s, the suction effect is strong enough to capture the clot despite the larger initial distance from the catheter. Hence, the pressure distribution and viscous stresses play essential roles in the suction or escape of the clot during the thrombectomy process. Also, the viscoelastic model predicts the rupture of the clot inside the catheter during suction. Full article

(This article belongs to the Special Issue Advances in Hemodynamics and Related Biological Flows)

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23 pages, 6282 KiB

Open AccessArticle

Computational Modeling of Droplet-Based Printing Using Multiphase Volume of Fluid (VOF) Method: Prediction of Flow, Spread Behavior, and Printability

by Rauf Shah and Ram V. Mohan

Fluids 2025, 10(5), 123; https://doi.org/10.3390/fluids10050123 - 8 May 2025

Abstract

The evolution of droplets during the printing process is modeled using the volume of fluid (VOF) method, which involves solving the Navier–Stokes and continuity equations for incompressible flow with multiple immiscible phases on a finite volume grid. An indicator function tracks the interfaces [...] Read more.

The evolution of droplets during the printing process is modeled using the volume of fluid (VOF) method, which involves solving the Navier–Stokes and continuity equations for incompressible flow with multiple immiscible phases on a finite volume grid. An indicator function tracks the interfaces and calculates surface tension forces. A grid independence study confirmed the convergence and efficacy of the solutions. The computational model agreed well with experimental data, accurately capturing the impact, spreading, and recoiling of droplets on a solid surface. Additionally, the model validated the interaction of droplets with hydrophilic and hydrophobic surfaces for both constant and dynamic contact angles. Key non-dimensional numbers (Re, We, Oh) were considered to study the interplay of forces during droplet impact on a solid surface. The final print quality is influenced by droplet dynamics, governed by body forces (surface tension, gravity), contact angle, dissipative forces due to motion, and material properties. Computational studies provide insights into the overall process performance and final print quality under various process conditions and material properties. Full article

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

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21 pages, 11237 KiB

Open AccessArticle

Investigation of Heat Transfer Enhancement Mechanisms in Elastic Tube Bundles Subjected to Exogenous Self-Excited Fluid Oscillation

by Jing Hu, Lei Guo and Shusheng Zhang

Fluids 2025, 10(5), 122; https://doi.org/10.3390/fluids10050122 - 8 May 2025

Abstract

Flow-induced vibration (FIV) characteristics are key factors in enhancing heat transfer. However, challenges such as insufficient heat transfer enhancement and the fatigue strength of the tube bundle persist in the context of improving the heat transfer in elastic tube bundle heat exchangers. This [...] Read more.

Flow-induced vibration (FIV) characteristics are key factors in enhancing heat transfer. However, challenges such as insufficient heat transfer enhancement and the fatigue strength of the tube bundle persist in the context of improving the heat transfer in elastic tube bundle heat exchangers. This study proposes a novel passive heat transfer enhancement paradigm for elastic tube bundles based on externally induced self-excited oscillations of fluid. By constructing a non-contact energy transfer system, the external oscillation energy is directed into the elastic tube bundle heat exchanger, achieving dynamic stress buffering and breaking through the steady-state flow heat transfer boundary layer. A three-dimensional fluid–structure interaction numerical model is established using Star CCM+2021.3 (16.06.008) to conduct a comparative analysis of the flow characteristics and heat transfer performance between the original structure without an oscillator and the improved structure equipped with a fluid oscillator. The results indicate that the improved structure, through the periodic unsteady jet induced by the fluid oscillator, significantly enhances the turbulence intensity of the shell-side fluid, with the turbulent kinetic energy increasing by over 50%. The radial flow area is notably expanded, thereby reducing the thermal resistance of the boundary layer. At cooling fluid velocities of 6 to 9 m/s, the heat transfer capability of the improved structure is enhanced by more than 50%. Compared with the original structure, the new structure, due to the loading of an external oscillation structure, causes the cold air to present a periodic up and down jet phenomenon. This jet phenomenon, on the one hand, increases the heat exchange area between the cold air and the outer surface of the tube bundle, thereby enhancing the heat exchange capacity. On the other hand, the large-area impact of the fluid reduces the thickness of the boundary layer, lowers the thermal resistance and thereby enhances the heat exchange capacity. Furthermore, this improved structure buffers the mechanical vibrations through self-excited oscillations of the fluid medium, ensuring that the stress levels in the tube bundle remain below the fatigue threshold, effectively mitigating the failure risks associated with traditional active vibration strategies. Full article

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26 pages, 10313 KiB

Open AccessArticle

Design of a Portable Integrated Fluid–Structure Interaction-Based Piezoelectric Flag Energy-Harvesting System

by Haochen Wang, Xingrong Huang, Zhe Li and Le Fang

Fluids 2025, 10(5), 121; https://doi.org/10.3390/fluids10050121 - 8 May 2025

Abstract

Fluid–structure interaction-based energy-harvesting technology has gained significant attention due to its potential for energy conversion. However, most existing studies primarily focus on energy capture, resulting in incomplete systems with limited portability and a lack of integrated circuitry. To address these limitations, this study [...] Read more.

Fluid–structure interaction-based energy-harvesting technology has gained significant attention due to its potential for energy conversion. However, most existing studies primarily focus on energy capture, resulting in incomplete systems with limited portability and a lack of integrated circuitry. To address these limitations, this study presents a portable, integrated piezoelectric flag energy-harvesting system that achieves a complete closed-loop conversion from fluid kinetic energy, through structural strain energy, to electrical energy. The system utilizes an upstream bluff body to generate vortex-induced vibrations, a downstream support structure that maintains operational stability, and an internally integrated wiring channel that enables overall energy conversion. Charge–discharge experiments on the energy storage unit enable a comprehensive evaluation of system performance, marking the first efficiency measurement of a fully integrated energy-harvesting system. Experimental results demonstrate the first quantified map of losses across all conversion stages in a portable piezo-flag platform, highlighting the system’s potential for powering small-scale, low-power self-sustaining devices. This work establishes a reference framework and provides a novel technological pathway for advancing practical applications of fluid-induced energy harvesting, contributing to the development of autonomous power sources in various engineering fields. Full article

(This article belongs to the Section Mathematical and Computational Fluid Mechanics)

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21 pages, 7419 KiB

Open AccessArticle

On Numerical Simulations of Turbulent Flows over a Bluff Body with Aerodynamic Flow Control Based on Trapped Vortex Cells: Viscous Effects

by Dmitry A. Lysenko

Fluids 2025, 10(5), 120; https://doi.org/10.3390/fluids10050120 - 8 May 2025

Abstract

Turbulent flows over a semi-circular cylinder (a limiting case of a thick airfoil with a chord equal to the diameter base) are investigated using high-fidelity large-eddy simulations at a diameter-based Reynolds number, Re = 130,000, Mach number, M = 0.05, and a zero [...] Read more.

Turbulent flows over a semi-circular cylinder (a limiting case of a thick airfoil with a chord equal to the diameter base) are investigated using high-fidelity large-eddy simulations at a diameter-based Reynolds number, Re = 130,000, Mach number, M = 0.05, and a zero angle of attack. The aerodynamic flow control system, designed with two trapped vortex cells, achieves a complete non-separated flow over the bluff body, except for low-scale turbulence effects, reaching approximately 80% of the theoretical lift coefficient limit (

2 π

for the half-circular airfoil). Viscous effects are analyzed using the conventional Reynolds-averaged Navier–Stokes approach for a broad range of Reynolds numbers, 75,000 ≤ Re ≤ 1,000,000. Numerical results demonstrate that the aerodynamic properties of the implemented concept are independent of the Reynolds number within this interval, highlighting its significant potential for further development. Full article

(This article belongs to the Collection Feature Paper for Mathematical and Computational Fluid Mechanics)

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21 pages, 8781 KiB

Open AccessArticle

Optimizing the Mobile Pump and Its Equipment to Reduce the Risk of Pluvial Flooding

by Horas Yosua, Muhammad Syahril Badri Kusuma, Joko Nugroho, Eka Oktariyanto Nugroho and Deni Septiadi

Fluids 2025, 10(5), 119; https://doi.org/10.3390/fluids10050119 - 7 May 2025

Abstract

Pluvial flooding in South Jakarta poses significant economic disruptions, requiring efficient mitigation strategies. This study focuses on optimizing mobile pump deployment as a non-structural flood control measure. Despite the use of mobile pumps in flood response, there is limited research on their systematic [...] Read more.

Pluvial flooding in South Jakarta poses significant economic disruptions, requiring efficient mitigation strategies. This study focuses on optimizing mobile pump deployment as a non-structural flood control measure. Despite the use of mobile pumps in flood response, there is limited research on their systematic optimization for pluvial flood mitigation. This study presents a transferable framework for deploying mobile pumps to mitigate pluvial flood risks in urban areas, demonstrated through a case study in South Jakarta, Indonesia. The findings indicate that flood depths of 75 cm have a 20–50% probability of occurrence, and rainfall in South Jakarta follows a distinct hourly distribution, with 56.6% of the rainfall occurring in the first hour and 43.4% in the second. Radar imagery from the BMKG is used here as the main tool for real-time rainfall detection. The optimization framework considers channel capacity, flood frequency, impact severity, accessibility, and operational protocols. Among 29 flood-prone locations analyzed, 8 of them require mobile pump intervention. Seven locations benefit from integration with weather prediction tools and SCADA systems, while three require dedicated operational procedures (SOPs). Simulation results indicate that placing mobile pumps near the upstream section of the flooded area yields the most effective flood reduction. A minimum pump capacity of 0.5 m³/s is recommended for optimal performance. This study demonstrates that strategic mobile pump deployment, coupled with predictive tools, significantly reduces pluvial flood risks in South Jakarta and offers a transferable framework for other urban areas. Full article

(This article belongs to the Special Issue Environmental Hydraulics, Turbulence and Sediment Transport, 3rd Edition)

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