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Volume 10
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Fluids, Volume 10, Issue 5 (May 2025) – 18 articles

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16 pages, 6195 KiB  
Article
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)
23 pages, 6283 KiB  
Article
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  
Article
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, 10301 KiB  
Article
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)
21 pages, 7419 KiB  
Article
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 (2π 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  
Article
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
Viewed by 19
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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29 pages, 13402 KiB  
Article
Modeling Microplastic Dispersion in the Salado Estuary Using Computational Fluid Dynamics
by Luis Velazquez-Araque, José Flor, Alfredo Méndez and Maritza Cárdenas-Calle
Fluids 2025, 10(5), 118; https://doi.org/10.3390/fluids10050118 - 6 May 2025
Viewed by 100
Abstract
Microplastics (MPs) have emerged as a major pollutant in aquatic ecosystems, primarily originating from industrial activities and plastic waste degradation. Understanding their transport dynamics is crucial for assessing environmental risks and developing mitigation strategies. This study employs Computational Fluid Dynamics (CFD) simulations to [...] Read more.
Microplastics (MPs) have emerged as a major pollutant in aquatic ecosystems, primarily originating from industrial activities and plastic waste degradation. Understanding their transport dynamics is crucial for assessing environmental risks and developing mitigation strategies. This study employs Computational Fluid Dynamics (CFD) simulations to model the trajectory of MPs in section B of the Salado Estuary in the city of Guayaquil, Ecuador, using ANSYS FLUENT 2024 R2. The transient behavior of Polyethylene Terephthalate (PET) particles was analyzed using the Volume of Fluid (VOF) multiphase model, k-omega SST turbulence model, and Discrete Phase Model (DPM) under a continuous flow regime. Spherical PET particles (5 mm diameter, 1340 kg/m3 density) were used to establish a simplified baseline scenario. Two water velocities, 0.5 m/s and 1.25 m/s, were selected based on typical flow rates reported in similar estuarine systems. Density contour analysis facilitated the modeling of the air-water interface, while particle trajectory analysis revealed that at 0.5 m/s, particles traveled 18–22.5 m before sedimentation, whereas at 1.25 m/s, they traveled 50–60 m before reaching the bottom. These findings demonstrate that higher flow velocities enhance MP transport distances before deposition, emphasizing the role of hydrodynamics in microplastic dispersion. While limited to one particle type and idealized conditions, this study underscores the potential of CFD as a predictive tool for assessing MP behavior in aquatic environments, contributing to improved pollution control and remediation efforts. Full article
(This article belongs to the Section Flow of Multi-Phase Fluids and Granular Materials)
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37 pages, 1062 KiB  
Review
The Universal Presence of the Reynolds Number
by Aldo Tamburrino and Yarko Niño
Fluids 2025, 10(5), 117; https://doi.org/10.3390/fluids10050117 - 1 May 2025
Viewed by 111
Abstract
The Reynolds number is a fundamental parameter in fluid dynamics, initially introduced by O. Reynolds in 1883 to characterize the transition between laminar and turbulent flow in fluids and necessary in the scaling of viscous resistance. Over time, its application has expanded significantly, [...] Read more.
The Reynolds number is a fundamental parameter in fluid dynamics, initially introduced by O. Reynolds in 1883 to characterize the transition between laminar and turbulent flow in fluids and necessary in the scaling of viscous resistance. Over time, its application has expanded significantly, becoming essential for studying a vast range of fluid phenomena—from microscopic scales such as cellular motion to macroscopic scales like turbulent flows and even intergalactic dynamics. The article highlights the universal relevance of the Reynolds number across various fields, including its adaptation to non-Newtonian fluids and granular flows. It emphasizes how the Reynolds number has evolved from a simple dimensionless group to a critical tool for understanding complex physical processes across different scales and environments. Full article
(This article belongs to the Special Issue Recent Advances in Fluid Mechanics: Feature Papers, 2024)
24 pages, 10198 KiB  
Article
Analysis of Two Protection Strategies for Reducing Aerosol Expulsion from Wind Instruments
by Miriam Baron, Bogac Tur, Marie Köberlein, Laila Ava Hermann, Sophia Gantner, Matthias Echternach and Stefan Kniesburges
Fluids 2025, 10(5), 116; https://doi.org/10.3390/fluids10050116 - 30 Apr 2025
Viewed by 83
Abstract
(1) Background: the aim of this study is to assess the effectiveness of two protection systems for aerosol cloud reduction while playing different wind instruments. (2) Methods: The protection systems used were a cotton molton construction combined with a bell filter attached at [...] Read more.
(1) Background: the aim of this study is to assess the effectiveness of two protection systems for aerosol cloud reduction while playing different wind instruments. (2) Methods: The protection systems used were a cotton molton construction combined with a bell filter attached at the bell of the instruments, as well as a household paper towel. For visualization of the emitted aerosol particles, e-cigarettes were used. With three full HD cameras, cloud dispersion was captured in the forward, sideways, and upwards directions. The effectiveness of aerosol spread reduction was statistically evaluated. (3) Results: Without protection, aerosol clouds dispersed, on average, up to 1.23 m in the forward direction, 0.46 m sideways, and 0.86 m upwards. The cotton molton mask reduced forward spread by 42%, while the paper towel achieved a 15% reduction, although both systems increased lateral and vertical dispersion. Specifically, the cotton molton mask yielded a 9% increase to the side and 7% in the upward direction, while the paper towel resulted in a 66% increase to the sides and a 10% increase in the upward direction. The cotton molton mask’s effectiveness was attributed to its additional coverage of the tone holes, which contribute to aerosol emission in woodwind instruments. A statistical analysis via the Friedman test confirmed significant reductions in forward dispersion with the cotton molton system. (4) Conclusions: Protective systems can partially reduce aerosol emissions. However, these alone are not sufficient, and further measures to reduce the spread of particles are necessary. Full article
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22 pages, 4445 KiB  
Article
Research on Dual-Mode Self-Calibration Tensioning System
by Xuling Liu, Yusong Zhang, Chaofeng Peng, Le Bo, Kaiyi Zhang, Guoyong Ye, Jinggan Shao, Jinghui Peng and Songjing Li
Fluids 2025, 10(5), 115; https://doi.org/10.3390/fluids10050115 - 30 Apr 2025
Viewed by 117
Abstract
In this paper, a double-mode self-calibration tension system is proposed, which adopts the conversion of hydraulic meter tension and the monitoring of standard force sensors. According to the material characteristics of the jack and the viscosity and temperature characteristics of the hydraulic oil, [...] Read more.
In this paper, a double-mode self-calibration tension system is proposed, which adopts the conversion of hydraulic meter tension and the monitoring of standard force sensors. According to the material characteristics of the jack and the viscosity and temperature characteristics of the hydraulic oil, the differential model of heat conduction in the hydraulic cylinder and the mathematical model of oil film friction heat generation are established, and the internal thermodynamic characteristics of the jack are theoretically analyzed, which provides theoretical support for the temperature compensation of the hydraulic oil pressure gauge of the jack. A simulation analysis was conducted on the thermodynamic characteristics of the hydraulic jack, and the distribution patterns of the temperature field, thermal stress field, and thermal strain field inside the hydraulic cylinder during normal operation were determined by measuring the temperature changes in five different parts of the jack at different times (t = 200 s, 2600 s, 5000 s, 7400 s, and 10,000 s). For the issue of heat generation due to oil film friction in the hydraulic jack, a simulation calculation model is developed by integrating Computational Fluid Dynamics (CFD) techniques with dynamic grid and slip grid methods. By simulating and analyzing frictional heating under conditions where the inlet pressures are 0.1 MPa, 0.3 MPa, 0.5 MPa, 0.7 MPa, and 0.9 MPa, respectively, we can obtain the temperature distribution on the jack, determine the frictional resistance, and subsequently conduct a theoretical analysis of the simulation results. Using the high-precision standard force sensor after data processing and the hydraulic oil gauge after temperature compensation, the online self-calibration of the tensioning system is carried out, and the regression equation of the tensioning system under different oil temperatures is obtained. The double-mode self-calibration tensioning system with temperature compensation is used to verify the compensation accuracy of the proposed double-mode self-calibration tensioning system. Full article
(This article belongs to the Topic Applied Heat Transfer)
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22 pages, 3296 KiB  
Article
Performance of an L-Shaped Duct OWC-WEC Integrated into Vertical and Sloped Breakwaters by Using a Free-Surface RANS-Based Numerical Model
by Eric Didier and Paulo R. F. Teixeira
Fluids 2025, 10(5), 114; https://doi.org/10.3390/fluids10050114 - 30 Apr 2025
Viewed by 174
Abstract
Waves generated by the wind in oceans and seas have a significant available quantity of clean and renewable energy. However, harvesting their energy is still a challenge. The integration of an oscillating water column (OWC) wave energy converter into a breakwater leads to [...] Read more.
Waves generated by the wind in oceans and seas have a significant available quantity of clean and renewable energy. However, harvesting their energy is still a challenge. The integration of an oscillating water column (OWC) wave energy converter into a breakwater leads to more viability, since it allows working as both harbor and coastal protection and harvesting wave energy. The main objective of this study is to investigate different configurations of L-shaped duct OWC devices inserted into vertical and sloped (2:3) impermeable breakwaters for different lengths of the lip by using a numerical model based on the Reynolds-Averaged Navier-Stokes equations. The ANSYS FLUENT® software (2016) is used in 2D numerical simulations by adopting the volume of fluid method to consider the two-phase free surface flow (water and air). It was observed that both the length of the lip and the length of the L-shaped duct OWC significantly influence the resonance and the efficiency of the OWC device. In addition, the performance of the OWC device varies significantly with its geometric configuration, which needs to be adapted for the local sea state. Full article
(This article belongs to the Special Issue Computational Fluid Dynamics Applied to Transport Phenomena)
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26 pages, 9399 KiB  
Article
Investigation of Multiphase Flow in Continuous-Casting Water Model with Measurements and Computational Modeling
by Hamed Olia, Dylan Palmer, Ehsan Jebellat and Brian G. Thomas
Fluids 2025, 10(5), 113; https://doi.org/10.3390/fluids10050113 - 28 Apr 2025
Viewed by 230
Abstract
This work introduces a 0.6-scale water model of the continuous slab-casting process and a MATLAB-based model to study the effects of non-primed and multiphase flow on pressure and flow rate. The water model uses stopper-rod flow control and features pressure and velocity measurements [...] Read more.
This work introduces a 0.6-scale water model of the continuous slab-casting process and a MATLAB-based model to study the effects of non-primed and multiphase flow on pressure and flow rate. The water model uses stopper-rod flow control and features pressure and velocity measurements at multiple locations. The new computational model, PFSR V4 (Pressure-drop Flow-rate model of Stopper Rod metal delivery systems, Version 4), improves upon a prior one-dimensional Bernoulli-based framework by incorporating a bubble accumulation zone. This zone represents a region of bubbly flow with an intermediate gas fraction between constant-pressure gas pockets below the stopper tip and the downstream bubbly flow regime. Parametric studies with the water model show that flow remains fully primed at low gas flow rates but transitions to non-primed flow as the gas flow rate exceeds 10–16 SLPM. Three different flow regions are observed inside the water model nozzle: air pocket, bubble accumulation, and bubbly flow, which are also captured by the new computational model. Above a critical gas flow rate, the flow becomes unstable and difficult to control, though higher hot gas flow rates are expected for similar transitions in a real steel caster due to gas expansion at high temperatures. Pressure changes are minimal in the air pocket region and increase significantly in the upper bubble accumulation zone, where liquid velocity is much higher than in the classic bubbly-flow region, found lower in the nozzle. The new model was successfully calibrated to match the observed flow regimes and shows good agreement with the water-model measurements. Full article
(This article belongs to the Special Issue Multiphase Flow for Industry Applications)
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19 pages, 5624 KiB  
Article
Research on the Improvement of BEM Method for Ultra-Large Wind Turbine Blades Based on CFD and Artificial Intelligence Technologies
by Shiyu Yang, Mingming Zhang, Yu Feng, Haikun Jia, Na Zhao and Qingwei Chen
Fluids 2025, 10(5), 112; https://doi.org/10.3390/fluids10050112 - 27 Apr 2025
Viewed by 164
Abstract
With the development of the wind power industry, wind turbine blades are increasingly adopting ultra-large-scale designs. However, as the size of blades continues to increase, existing aerodynamic calculation methods struggle to achieve both relatively high computational accuracy and efficiency simultaneously. To tackle this [...] Read more.
With the development of the wind power industry, wind turbine blades are increasingly adopting ultra-large-scale designs. However, as the size of blades continues to increase, existing aerodynamic calculation methods struggle to achieve both relatively high computational accuracy and efficiency simultaneously. To tackle this challenge, this research focuses on the low accuracy issues of the traditional Blade Element Momentum theory (BEM) in predicting the aerodynamic performance of wind turbine blades. Consequently, a correction framework is proposed, to integrate the Computational Fluid Dynamics (CFD) method with the Multilayer Perceptron (MLP) neural network. In this approach, the CFD method is used to predict the airflow characteristics around the blades, and the MLP neural network is employed to model the intricate functional relationships between multiple influencing factors and key aerodynamic parameters. This process results in high-precision predictive functions for key aerodynamic parameters, which are then used to correct the traditional BEM. When this correction framework is applied to the rotor of the IEA 15 MW wind turbine, the effectiveness of MLP in predicting key aerodynamic parameters is demonstrated. The research findings suggest that this framework can enhance the accuracy of BEM aerodynamic load predictions to a level comparable to that of RANS. Full article
(This article belongs to the Special Issue Drag Reduction Through Traditional or Machine Learning-Based Flow Control)
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15 pages, 326 KiB  
Article
Weakly Nonlinear Instability of a Convective Flow in a Plane Vertical Channel
by Natalja Budkina, Valentina Koliskina, Andrei Kolyshkin and Inta Volodko
Fluids 2025, 10(5), 111; https://doi.org/10.3390/fluids10050111 - 26 Apr 2025
Viewed by 123
Abstract
The weakly nonlinear stability analysis of a convective flow in a planar vertical fluid layer is performed in this paper. The base flow in the vertical direction is generated by internal heat sources distributed within the fluid. The system of Navier–Stokes equations under [...] Read more.
The weakly nonlinear stability analysis of a convective flow in a planar vertical fluid layer is performed in this paper. The base flow in the vertical direction is generated by internal heat sources distributed within the fluid. The system of Navier–Stokes equations under the Boussinesq approximation and small-Prandtl-number approximation is transformed to one equation containing a stream function. Linear stability calculations with and without a small-Prandtl-number approximation lead to the range of the Prantdl numbers for which the approximation is valid. The method of multiple scales in the neighborhood of the critical point is used to construct amplitude evolution equation for the most unstable mode. It is shown that the amplitude equation is the complex Ginzburg–Landau equation. The coefficients of the equation are expressed in terms of integrals containing the linear stability characteristics and the solutions of three boundary value problems for ordinary differential equations. The results of numerical calculations are presented. The type of bifurcation (supercritical bifurcation) predicted by weakly nonlinear calculations is in agreement with experimental data. Full article
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20 pages, 3854 KiB  
Article
EHD Instability Modes of Power-Law Fluid Jet Issuing in Gaseous Streaming via Permeable Media
by Mohamed F. El-Sayed, Mohamed F. E. Amer and Doaa M. Mostafa
Fluids 2025, 10(5), 110; https://doi.org/10.3390/fluids10050110 - 25 Apr 2025
Viewed by 214
Abstract
The instability of a non-Newtonian dielectric fluid jet of power-law (P-L) type injected when streaming dielectric gas through porous media is examined using electrohydrodynamic (EHD) linear analysis. The interfacial boundary conditions (BCs) are used to derive the dispersion relation for both shear-thinning (s-thin) [...] Read more.
The instability of a non-Newtonian dielectric fluid jet of power-law (P-L) type injected when streaming dielectric gas through porous media is examined using electrohydrodynamic (EHD) linear analysis. The interfacial boundary conditions (BCs) are used to derive the dispersion relation for both shear-thinning (s-thin) and shear-thickening (s-thick) fluids. A detailed discussion is outlined on the impact of dimensionless flow parameters. The findings show that jet breakup can be categorized into two instability modes: Rayleigh (RM) and Taylor (TM), respectively. For both fluids, the system in TM is found to be more unstable than that found in RM, and, for s-thick fluids, it is more unstable. For all P-L index values, the system is more unstable if a porous material exists than when it does not. It is demonstrated that the generalized Reynolds number (Ren), Reynolds number (Re), P-L index, dielectric constants, gas-to-liquid density, and viscosity ratios have destabilizing influences; moreover, the Weber number (We), electric field (EF), porosity, and permeability of the porous medium have a stabilizing impact. Depending on whether its value is less or more than one, the velocity ratio plays two different roles in stability, and the breakup length and size of P-L fluids are connected to the maximal growth level and the instability range in both modes. Full article
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37 pages, 15268 KiB  
Review
Subchannel Reactor Studies: Applications and Advances Using Lattice Boltzmann Method—Comprehensive Review Study
by Abutiatey Eugene and Pil-Seung Chung
Fluids 2025, 10(5), 109; https://doi.org/10.3390/fluids10050109 - 25 Apr 2025
Viewed by 164
Abstract
Computational fluid dynamics (CFD) is an instrumental tool used in tackling the challenges of flow behavior and safety within nuclear reactor cores. Traditional CFD methods like finite volume, finite element, and finite difference have driven significant progress in nuclear engineering, particularly in single-phase [...] Read more.
Computational fluid dynamics (CFD) is an instrumental tool used in tackling the challenges of flow behavior and safety within nuclear reactor cores. Traditional CFD methods like finite volume, finite element, and finite difference have driven significant progress in nuclear engineering, particularly in single-phase and two-phase flow modeling, multiscale analysis, and multiphysics coupling. However, the Lattice Boltzmann Method (LBM), an advancing CFD tool for nuclear reactor subchannel study, remains underexplored in this field. LBM takes a unique mesoscopic approach by modeling particle distributions on a discrete lattice, offering a bridge between microscopic dynamics and macroscopic continuum behavior. Since the integration of LBM into the Lattice Bhatnagar–Gross–Krook (LBGK) model, it has significantly advanced, proving its efficiency in handling complex flow conditions. This review explores the potential of LBM in nuclear reactor subchannel applications. This study emphasizes LBM as a robust computational tool for subchannel study by highlighting its strengths, limitations, and future possibilities. Full article
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13 pages, 987 KiB  
Article
Concentration Monitoring of Highly-Diluted Crude Oil-In-Water Emulsions by Ultrasonic Backscattering Sensors
by Carlos A. B. Reyna, Ediguer E. Franco, Santiago Laín, Timoteo F. de Oliveira, Marcos S. G. Tsuzuki and Flávio Buiochi
Fluids 2025, 10(5), 108; https://doi.org/10.3390/fluids10050108 - 25 Apr 2025
Viewed by 211
Abstract
This work deals with the feasibility of ultrasonic monitoring of the crude oil content in highly diluted crude oil-in-water emulsions, common mixtures obtained in the coalescence process of the petroleum industry. The measurement principle is the determination of the time of flight using [...] Read more.
This work deals with the feasibility of ultrasonic monitoring of the crude oil content in highly diluted crude oil-in-water emulsions, common mixtures obtained in the coalescence process of the petroleum industry. The measurement principle is the determination of the time of flight using the reflected pulses from a set of scatterers located in the near field of commercial transducers of 5 and 10 MHz. Dispersers consist of two rows of metal wires tensioned in front of the transducer using a specially designed mechanical part. The resulting assembly is a probe that can be introduced into a tank or pipe to perform the measurement. Experiments with crude oil-in-water emulsions with concentrations from 10 to 2000 ppm (parts per million) at a temperature of 20 °C were carried out. The results show that the small changes in the propagation velocity resulting from changes in concentration and temperature can be detected by the developed ultrasonic sensor. This opens up the possibility of determining the oil content in the emulsion by means of a calibration approach. The main motivation is the development of techniques for real-time monitoring of crude oil content in the wastewater produced in the petroleum industry. Full article
(This article belongs to the Special Issue Numerical Modeling and Experimental Studies of Two-Phase Flows, 2nd Edition)
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18 pages, 6280 KiB  
Article
Hydrodynamic Resistance Analysis of Large Biomimetic Yellow Croaker Model: Effects of Shape, Body Length, and Material Based on CFD
by Donglei Zhao, Kexiang Lu and Weiguo Qian
Fluids 2025, 10(5), 107; https://doi.org/10.3390/fluids10050107 - 24 Apr 2025
Viewed by 201
Abstract
The marine environment is highly complex, characterized by substantial fluctuations in flow velocity. To enhance the adaptability of robotic large yellow croakers to such conditions, this study takes into account multiple factors, including shape, dimensions, and material properties, and evaluates their hydrodynamic resistance [...] Read more.
The marine environment is highly complex, characterized by substantial fluctuations in flow velocity. To enhance the adaptability of robotic large yellow croakers to such conditions, this study takes into account multiple factors, including shape, dimensions, and material properties, and evaluates their hydrodynamic resistance characteristics. A 2D model of large yellow croakers aged 1, 4, 7, 10, and 12 months was established as the bionic object. Based on computational fluid dynamics, the water resistance characteristics of this model were investigated in the same water environment. A 3D model of this species based on the 2D model and three skin materials, PE, PC, and ST, was added, and the effects of these materials on the water resistance of the 3D model were investigated. It was shown that in a water environment with a current speed of 0.1~1 m/s, the water resistance of large yellow croaker models at different ages ranged from 0.1006 to 6.8485 N; that of croakers with different body lengths ranged from 0.1067 to 28.5760 N; and that of croakers with different skin materials ranged from 0.0048 to 0.8672 N. The results showed that in the water environment with a current speed of 0.1–1 m/s, the 12-month-old large yellow croaker model had a lower water resistance range of 0.1006~3.6512 N in the watershed compared with other models of the same age; the large yellow croaker models with body lengths of 20, 30, and 40 cm had a smaller range of water resistance of 0.1125~12.5110 N in the watershed compared with other models of the same body length; and large yellow croaker models made of PE had a smaller range of resistance of 0.0048~0.7523 N in the watershed compared to those made of PC and ST materials. The results of this study are important for the design and fabrication of robotic fish capable of prolonged underwater operations. Full article
(This article belongs to the Section Mathematical and Computational Fluid Mechanics)
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