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Volume 10
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Fluids, Volume 10, Issue 1 (January 2025) – 20 articles

Cover Story (view full-size image): Through the analysis of ventricular blood flow distribution, we characterized the kinetic energy expenditure within the left ventricle caused by the bicuspid aortic valve. We also provide new evidence regarding the kinetic energy increment due to the bicuspid aortic valve phenotype and its subsequent correlation with surgical referral. View this paper
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24 pages, 6157 KiB  
Article
Machine Learning Model for Gas–Liquid Interface Reconstruction in CFD Numerical Simulations
by Tamon Nakano, Michele Alessandro Bucci, Jean-Marc Gratien and Thibault Faney
Fluids 2025, 10(1), 20; https://doi.org/10.3390/fluids10010020 - 20 Jan 2025
Viewed by 504
Abstract
The volume of fluid (VoF) method is widely used in multiphase flow simulations to track and locate the interface between two immiscible fluids. The relative volume fraction in each cell is used to recover the interface properties (i.e., normal, location, and curvature). Accurate [...] Read more.
The volume of fluid (VoF) method is widely used in multiphase flow simulations to track and locate the interface between two immiscible fluids. The relative volume fraction in each cell is used to recover the interface properties (i.e., normal, location, and curvature). Accurate computation of the local interface curvature is essential for evaluation of the surface tension force at the interface. However, this interface reconstruction step is a major bottleneck of the VoF method due to its high computational cost and low accuracy on unstructured grids. Recent attempts to apply data-driven approaches to this problem have outperformed conventional methods in many test cases. However, these machine learning-based methods are restricted to computations on structured grids. In this work, we propose a machine learning-enhanced VoF method based on graph neural networks (GNNs) to accelerate interface reconstruction on general unstructured meshes. We first develop a methodology for generating a synthetic dataset based on paraboloid surfaces discretized on unstructured meshes to obtain a dataset akin to the configurations encountered in industrial settings. We then train an optimized GNN architecture on this dataset. Our approach is validated using analytical solutions and comparisons with conventional methods in the OpenFOAM framework on a canonical test. We present promising results for the efficiency of GNN-based approaches for interface reconstruction in multiphase flow simulations in the industrial context. Full article
(This article belongs to the Special Issue Advances in Multiphase Flow Simulation with Machine Learning)
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25 pages, 5652 KiB  
Article
Vaporization Dynamics of a Volatile Liquid Jet on a Heated Bubbling Fluidized Bed
by Subhasish Mitra and Geoffrey M. Evans
Fluids 2025, 10(1), 19; https://doi.org/10.3390/fluids10010019 - 18 Jan 2025
Viewed by 436
Abstract
In this paper, droplet vaporization dynamics in a heated bubbling fluidized bed was studied. A volatile hydrocarbon liquid jet comprising acetone was injected into a hot bubbling fluidized bed of Geldart A-type glass ballotini particles heated at 150 °C, well above the saturation [...] Read more.
In this paper, droplet vaporization dynamics in a heated bubbling fluidized bed was studied. A volatile hydrocarbon liquid jet comprising acetone was injected into a hot bubbling fluidized bed of Geldart A-type glass ballotini particles heated at 150 °C, well above the saturation temperature of acetone (56 °C). Intense interactions were observed among the evaporating droplets and hot particles during contact with the re-suspension of particles due to a release of vapour. A non-intrusive schlieren imaging method was used to track the hot air and vapour mixture plume in the freeboard region of the bed and the acetone vapour fraction therein was mapped. The jet vaporization dynamics in the bubbling fluidized bed was modelled in a Eulerian–Lagrangian CFD (computational fluid dynamics) modelling framework involving heat and mass transfer sub models. The CFD model indicated a dispersion of the vapour plume from the evaporating droplets which was qualitatively compared with the schlieren images. Further, the CFD simulation predicted a significant reduction (~60 °C) in the local bed temperature at the point of the jet injection, which was indirectly confirmed in an experiment by the presence of particle agglomerates. Full article
(This article belongs to the Special Issue Experimental and Computational Advances in Bubbling Fluidized Beds Hydrodynamics)
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21 pages, 1511 KiB  
Article
Parametric Instabilities in Time-Varying Compressible Linear Flows
by Ioannis Kiorpelidis and Nikolaos A. Bakas
Fluids 2025, 10(1), 18; https://doi.org/10.3390/fluids10010018 - 18 Jan 2025
Viewed by 272
Abstract
The stability of time-dependent compressible linear flows, which are characterized by periodic variations in either their shape or their shear, is investigated. Two novel parametric instabilities are found: an instability that occurs for periodically wobbling elliptic vortices at a number of discrete oscillation [...] Read more.
The stability of time-dependent compressible linear flows, which are characterized by periodic variations in either their shape or their shear, is investigated. Two novel parametric instabilities are found: an instability that occurs for periodically wobbling elliptic vortices at a number of discrete oscillation frequencies that are proportional to the Mach number and an instability that occurs for all linear flows at various frequencies of the shear oscillation that depend on the Mach number. In addition, the physical mechanism underlying the instabilities is explained in terms of the linear interaction of three waves with time-varying wavevectors that describe the evolution of perturbations: a vorticity wave representing the evolution of incompressible perturbations and two counter-propagating acoustic waves. Elliptical instability occurs because the scale of the acoustic waves decreases exponentially and their wave action is conserved, leading to an exponential increase in the acoustic waves’ energies. The instability in shear-varying flows is driven by the interaction between vorticity and the acoustic waves, which couple through the shear and for specific frequencies resonate parametrically, leading to exponential or linear growth. Full article
(This article belongs to the Special Issue Compressible Flows)
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20 pages, 9877 KiB  
Article
Three-Dimensional Aeroelastic Investigation of a Novel Convex Bladed H-Darrieus Wind Turbine Based on a Two-Way Coupled Computational Fluid Dynamics and Finite Element Analysis Approach
by Tarek Elbeji, Wael Ben Amira, Khaled Souaissa, Moncef Ghiss, Hatem Bentaher and Nabil Ben Fredj
Fluids 2025, 10(1), 17; https://doi.org/10.3390/fluids10010017 - 18 Jan 2025
Viewed by 660
Abstract
H-Darrieus vertical-axis wind turbines (VAWTs) capture wind regardless of its direction and operate effectively even in challenging and turbulent wind conditions. As a result, the blades operate under erratic and intricate aerodynamic loads, which cause them to bend. The performance of the H-Darrieus [...] Read more.
H-Darrieus vertical-axis wind turbines (VAWTs) capture wind regardless of its direction and operate effectively even in challenging and turbulent wind conditions. As a result, the blades operate under erratic and intricate aerodynamic loads, which cause them to bend. The performance of the H-Darrieus rotor will therefore be impacted by the blade’s deflection. This study aims at investigating the dynamic aerostructure influence on a novel convex-bladed H-Darrieus geometry. The results are compared to a straight-bladed baseline rotor. To do so, a two-way fluid–structure interaction (FSI)-coupled approach is performed to accurately address this issue. This approach allows for the simultaneous resolution of the fluid flow around the rotor and the mechanical structure responses inside the blades. The turbulent flows are resolved using the k-ω-SST model together with the URANS equations through computational fluid dynamics (CFD), while the structural deflections of the blades are assessed using finite element analysis (FEA). The results show that the performance of both H-Darrieus turbines decreases with increasing deformation. In addition, the study found that the carbon fiber composite (M1) material has the least deformation in the convex and straight blades, with values of 9.1 mm and 20.331 mm, respectively. The glass-fiber-reinforced epoxy composite (M3) material shows the most significant deflection across both types, with displacements of 32.50 mm and 73.78 mm for the straight blade and 19.02 mm and 43.03 mm for the convex blade. This study also reveals that the straight blade has a peak displacement of 73.785 mm when using the M3 material at TSR = 3, while the convex blade has a minimum displacement of 20.331 mm when using the M1 material, highlighting the varying performance characteristics of the materials. The maximum stress observed occurs in the straight blade, registering at 324.1 MPa with TSR = 3, which aligns closely with the peak displacement values, particularly for the aluminum alloy material (M2). In contrast, the convex blade made from the first material (M1) exhibits the lowest stress levels among the tested configurations. Full article
(This article belongs to the Special Issue Computational Fluid Dynamics in Fluid Machinery)
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23 pages, 7164 KiB  
Article
Transformations in Flow Characteristics and Fluid Force Reduction with Respect to the Vegetation Type and Its Installation Position Downstream of an Embankment
by A H M Rashedunnabi, Norio Tanaka and Md Abedur Rahman
Fluids 2025, 10(1), 16; https://doi.org/10.3390/fluids10010016 - 17 Jan 2025
Viewed by 363
Abstract
Compound mitigation systems, integrations of natural and engineering structures against the high inundating current from tsunamis or storm surges, have garnered significant interest among researchers, especially following the Tohoku earthquake and tsunami in 2011. Understanding the complex flow phenomena is essential for the [...] Read more.
Compound mitigation systems, integrations of natural and engineering structures against the high inundating current from tsunamis or storm surges, have garnered significant interest among researchers, especially following the Tohoku earthquake and tsunami in 2011. Understanding the complex flow phenomena is essential for the resilience of the mitigation structures and effective energy reduction. This study conducted a flume experiment to clarify flow characteristics and fluid force dissipation in a compound defense system. Vegetation models (V) with different porosities (Φ) were placed at three different positions downstream of an embankment model (E). A single-layer emergent vegetation model was considered, and a short-layer vegetation with several values of Φ was incorporated to increase its density (decreased Φ). Depending on Φ and the spacing (S) between the E and V, hydraulic jumps occurred in the physical system. The findings demonstrated that a rise in S allowed a hydraulic jump to develop inside the system and contributed to reducing the fluid force in front and downstream of V. Due to the reduced porosity of the double-layer vegetation, the hydraulic jump moved upstream and terminated within the system, resulting in a uniform water surface upstream of V and downstream of the system. As a result, the fluid force in front of and behind V reduced remarkably. Full article
(This article belongs to the Special Issue Environmental Hydraulics, Turbulence and Sediment Transport, 3rd Edition)
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3 pages, 132 KiB  
Editorial
Industrial CFD and Fluid Modelling in Engineering
by Francesco De Vanna
Fluids 2025, 10(1), 15; https://doi.org/10.3390/fluids10010015 - 17 Jan 2025
Viewed by 393
Abstract
Fluids is proud to present the Special Issue “Industrial CFD and Fluid Modelling in Engineering”, a carefully curated collection of pioneering research that underscores the transformative role of Computational Fluid Dynamics (CFD) in addressing the challenges of industrial fluid mechanics [...] Full article
(This article belongs to the Special Issue Industrial CFD and Fluid Modelling in Engineering)
17 pages, 6420 KiB  
Article
Impact of Solid Particle Concentration and Liquid Circulation on Gas Holdup in Counter-Current Slurry Bubble Columns
by Sadra Mahmoudi and Mark W. Hlawitschka
Fluids 2025, 10(1), 14; https://doi.org/10.3390/fluids10010014 - 16 Jan 2025
Viewed by 396
Abstract
In this study, in a three-phase reactor with a rectangular cross-section, the effects of liquid circulation rates and solid particle concentration on gas holdup and bubble size distribution (BSD) were investigated. Air, water, and glass beads were used as the gas, liquid, and [...] Read more.
In this study, in a three-phase reactor with a rectangular cross-section, the effects of liquid circulation rates and solid particle concentration on gas holdup and bubble size distribution (BSD) were investigated. Air, water, and glass beads were used as the gas, liquid, and solid phases, respectively. Different liquid circulation velocities and different solid loads were applied. The results demonstrate that increasing solid content from 0% to 6% can decrease gas holdup by 50% (due to increased slurry phase viscosity and promotion of bubble coalescence). Also, increasing the liquid circulation rate showed a weak effect on gas holdup, although a slight incremental effect was observed due to the promotion of bubble breakup and the extension of bubble residence time. The gas holdup in counter-current slurry bubble columns (CCSBCs) was predicted using a novel correlation that took into account the combined effects of solid concentration and liquid circulation rate. These findings are crucial for the design and optimization of the three-phase reactors used in industries such as mining and wastewater treatment. Full article
(This article belongs to the Special Issue Mass Transfer in Multiphase Reactors)
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19 pages, 7229 KiB  
Article
Impact of Rock Cuttings on Downhole Fluid Movement in Polycrystalline Diamond Compact (PDC) Bits, Computational Fluid Dynamics, Simulation, and Optimization of Hydraulic Structures
by Lihong Wei and Jaime Honra
Fluids 2025, 10(1), 13; https://doi.org/10.3390/fluids10010013 - 14 Jan 2025
Viewed by 378
Abstract
The flow occurring at the bottom of a polycrystalline diamond compact (PDC) drill bit involves a complex process made up of drilling fluid and the drilled rock cuttings. A thorough understanding of the bottom-hole flow conditions is essential for accurately evaluating and optimizing [...] Read more.
The flow occurring at the bottom of a polycrystalline diamond compact (PDC) drill bit involves a complex process made up of drilling fluid and the drilled rock cuttings. A thorough understanding of the bottom-hole flow conditions is essential for accurately evaluating and optimizing the hydraulic structure design of the PDC drill bit. Based on a comprehensive understanding of the hydraulic structure and fluid flow characteristics of PDC drill bits, this study integrates computational fluid dynamics (CFD) with rock-breaking simulation methods to refine and enhance the numerical simulation approach for the liquid–solid two-phase flow field of PDC drill bits. This study further conducts a comparative analysis of simulation results between single-phase and liquid–solid two-phase flows, highlighting the influence of rock cuttings on flow dynamics. The results reveal substantial differences in flow behavior between single-phase and two-phase conditions, with rock cuttings altering the velocity distribution, flow patterns, and hydraulic performance near the bottom-hole region of the drill bit. The two-phase flow simulation results demonstrate higher accuracy and provide a more detailed depiction of the bottom-hole flow, facilitating the identification of previously unrecognized issues in the hydraulic structure design. These findings advance the methodology for multiphase flow simulation in PDC drill bit studies, providing significant academic and engineering value by offering actionable insights for optimizing hydraulic structures and extending bit life. Full article
(This article belongs to the Special Issue Recent Advances in Single and Multiphase Flows in Microchannels, 3rd Edition)
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19 pages, 9368 KiB  
Article
On the Effect of Gas Content in Centrifugal Pump Operations with Non-Newtonian Slurries
by Nicola Zanini, Alessio Suman, Mattia Piovan and Michele Pinelli
Fluids 2025, 10(1), 12; https://doi.org/10.3390/fluids10010012 - 8 Jan 2025
Viewed by 451
Abstract
Non-Newtonian fluids are widespread in industry, e.g., biomedical, food, and oil and gas, and their rheology plays a fundamental role in choosing the processing parameters. Centrifugal pumps are widely employed to ensure the displacement of a huge amount of fluids due to their [...] Read more.
Non-Newtonian fluids are widespread in industry, e.g., biomedical, food, and oil and gas, and their rheology plays a fundamental role in choosing the processing parameters. Centrifugal pumps are widely employed to ensure the displacement of a huge amount of fluids due to their robustness and reliability. Since the pump performance is usually provided by manufacturers only for water, the selection of a proper pump to handle non-Newtonian fluids may prove very tricky. On-field experiences in pump operations with non-Newtonian slurries report severe head and efficiency drops, especially in part-load operations, whose causes are still not fully understood. Several models are found in the literature to predict the performance of centrifugal pumps with this type of fluids, but a lack of reliability and generality emerges. In this work, an extensive experimental campaign is carried out with an on-purpose test bench to investigate the effect of non-Newtonian shear-thinning fluids on the performance of a small commercial centrifugal pump. A dedicated experimental campaign is conducted to study the causes of performance drops. The results allow to establish a relationship between head and efficiency drops with solid content in the mixture. Sudden performance drops and unstable operating points are detected in part-load operations and the most severe drops are detected with the higher kaolin content in the mixture. Performance drop investigation allows to ascribe performance drop to gas-locking phenomena. Finally, a critical analysis is proposed to relate the resulting performance with both fluids’ rheology and the gas fraction trapped in the fluid. The results here presented can be useful for future numerical validation and predicting performance models. Full article
(This article belongs to the Special Issue Advances in Computational Mechanics of Non-Newtonian Fluids)
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1 pages, 120 KiB  
Retraction
RETRACTED: Fatunmbi et al. Irreversibility Analysis for Eyring–Powell Nanoliquid Flow Past Magnetized Riga Device with Nonlinear Thermal Radiation. Fluids 2021, 6, 416
by Ephesus Olusoji Fatunmbi, Adeshina Taofeeq Adeosun and Sulyman Olakunle Salawu
Fluids 2025, 10(1), 11; https://doi.org/10.3390/fluids10010011 - 8 Jan 2025
Viewed by 267
Abstract
The Fluids Editorial Office retracts the article “Irreversibility Analysis for Eyring–Powell Nanoliquid Flow Past Magnetized Riga Device with Nonlinear Thermal Radiation” [...] Full article
30 pages, 16206 KiB  
Review
Literature Review on Single and Twin-Screw Extruders Design for Polymerization Using CFD Simulation
by Elham Delvar, Inês Oliveira, Margarida S. C. A. Brito, Cláudia G. Silva, Arantzazu Santamaria-Echart, Maria-Filomena Barreiro and Ricardo J. Santos
Fluids 2025, 10(1), 9; https://doi.org/10.3390/fluids10010009 - 7 Jan 2025
Viewed by 706
Abstract
This work presents a comprehensive review of the evolution in modeling reactive extrusion (REx), tracing developments from early analytical models to advanced computational fluid dynamics (CFD) simulations. Additionally, it highlights the key challenges and future directions in this field. Analytical models to describe [...] Read more.
This work presents a comprehensive review of the evolution in modeling reactive extrusion (REx), tracing developments from early analytical models to advanced computational fluid dynamics (CFD) simulations. Additionally, it highlights the key challenges and future directions in this field. Analytical models to describe the velocity profiles were proposed in the 1950s, involving certain geometrical simplifications. However, numerical models of melt polymeric flow in extruders have proven to be crucial for optimizing screw design and predicting process characteristics. The state-of-the-art CFD models for single and twin-screw extruders design address the impact of geometry (type of mixing elements and geometrical simplifications of CFD geometries), pressure and temperature gradients, and quantification of mixing. Despite the extensive work conducted, modeling reactive extrusion using CFD remains challenging due to the intricate interplay of mixing, heat transfer, chemical reactions, and non-Newtonian fluid behavior under high shear and temperature gradients. These challenges are further intensified by the presence of multiphase flows and the complexity of extruder geometries. Future advancements should enhance simulation accuracy, incorporate multiphase flow models, and utilize real-time sensor data for adaptive modeling approaches. Full article
(This article belongs to the Special Issue Industrial CFD and Fluid Modelling in Engineering, 2nd Edition)
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26 pages, 16492 KiB  
Article
Predictive Analysis of Structural Damage in Submerged Structures: A Case Study Approach Using Machine Learning
by Alexandre Brás dos Santos, Hugo Mesquita Vasconcelos, Tiago M. R. M. Domingues, Pedro J. S. C. P. Sousa, Susana Dias, Rogério F. F. Lopes, Marco L. P. Parente, Mário Tomé, Adélio M. S. Cavadas and Pedro M. G. P. Moreira
Fluids 2025, 10(1), 10; https://doi.org/10.3390/fluids10010010 - 7 Jan 2025
Viewed by 466
Abstract
This study focuses on the development of a machine learning (ML) model to elaborate on predictions of structural damage in submerged structures due to ocean states and subsequently compares it to a real-life case of a 6-month experiment with a benthic lander bearing [...] Read more.
This study focuses on the development of a machine learning (ML) model to elaborate on predictions of structural damage in submerged structures due to ocean states and subsequently compares it to a real-life case of a 6-month experiment with a benthic lander bearing a multitude of sensors. The ML model uses wave parameters such as height, period and direction as input layers, which describe the ocean conditions, and strains in selected points of the lander structure as output layers. To streamline the dataset generation, a simplified approach was adopted, integrating analytical formulations based on Morison equations and numerical simulations through the Finite Element Method (FEM) of the designed lander. Subsequent validation involved Fluid–Structure Interaction (FSI) simulations, using a 2D Computational Fluid Dynamics (CFD)-based numerical wave tank of the entire ocean depth to access velocity profiles, and a restricted 3D CFD model incorporating the lander structure. A case study was conducted to empirically validate the simulated ML model, with the design and deployment of a benthic lander at 30 m depth. The lander was monitored using electrical and optical strain gauges. The strains measured during the testing period will provide empirical validation and may be used for extensive training of a more reliable model. Full article
(This article belongs to the Special Issue Industrial CFD and Fluid Modelling in Engineering, 2nd Edition)
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3 pages, 121 KiB  
Editorial
Fluids and Surfaces
by Manfredo Guilizzoni
Fluids 2025, 10(1), 8; https://doi.org/10.3390/fluids10010008 - 6 Jan 2025
Viewed by 409
Abstract
Fluids is pleased to present a Special Issue named “Fluids and Surfaces”, a curated collection of ten research articles focused on capillary phenomena and the interaction between fluids and surfaces [...] Full article
(This article belongs to the Special Issue Fluids and Surfaces)
12 pages, 3759 KiB  
Article
Numerical Simulation of First-Order Surface Reaction in Open Cavity Using Lattice Boltzmann Method
by Cristian Yoel Quintero-Castañeda, María Margarita Sierra-Carrillo, Arturo I. Villegas-Andrade and Javier Burgos-Vergara
Fluids 2025, 10(1), 7; https://doi.org/10.3390/fluids10010007 - 30 Dec 2024
Viewed by 497
Abstract
The lattice Boltzmann method (LBM) is a finite element and finite volume method for studying the reaction rate, mass diffusion and concentration of species. We are used the LBM to investigate the effect of the Damköhler number (Da) and Reynolds number (Re) on [...] Read more.
The lattice Boltzmann method (LBM) is a finite element and finite volume method for studying the reaction rate, mass diffusion and concentration of species. We are used the LBM to investigate the effect of the Damköhler number (Da) and Reynolds number (Re) on the laminar flow in a channel with an open square cavity and a reactive bottom wall in two dimensions in a first-order chemical reaction. The reactant A is transported through the cavity, where it undergoes a reaction on the reactive surface, resulting in the synthesis of product B. The effect of Da < 1 on the reaction rate is negligible for all investigated Re values; the generation of product B is slower because of the effect of the momentum diffusivity on the velocity inside the cavity. For Re = 5 and 1 < Da ≤ 100, the concentration of B inside the cavity reaches the maximum for Da = 100, and A is absorbed almost entirely on the bottom of the cavity. In our simulations, we observed that for all values of Re and Da > 100, the effect of the momentum diffusivity is negligible in the cavity, and the reaction on the surface is almost instantaneous. Full article
(This article belongs to the Special Issue Lattice Boltzmann Methods: Fundamentals and Applications)
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15 pages, 3667 KiB  
Article
Investigation of the Pulmonary Artery Hypertension Using an Ad Hoc OpenFOAM CFD Solver
by Francesco Duronio and Paola Marchetti
Fluids 2025, 10(1), 6; https://doi.org/10.3390/fluids10010006 - 29 Dec 2024
Viewed by 598
Abstract
Cardiovascular diseases are a group of disorders that affect the heart and blood vessels, representing a leading cause of death worldwide. With the help of computational fluid dynamics, it is possible to study the hemodynamics of the pulmonary arteries in detail and simulate [...] Read more.
Cardiovascular diseases are a group of disorders that affect the heart and blood vessels, representing a leading cause of death worldwide. With the help of computational fluid dynamics, it is possible to study the hemodynamics of the pulmonary arteries in detail and simulate various physiological conditions, thus offering numerous advantages over invasive analyses in the phases of diagnosis and surgical planning. Specifically, the aim of this study is the fluid dynamic analysis of the pulmonary artery, comparing the characteristics of the blood flow in a healthy subject with that of a patient affected by pulmonary arterial hypertension. We performed CFD simulations with the OpenFOAM C++ library using a purposely developed solver that features the Windkessel model as a pressure boundary condition. This methodology, scarcely applied in the past for this problem, allows for a proficient analysis and the detailed quantification of the most important fluid-dynamic parameters (flow velocity, pressure distribution, and wall shear stress (WSS)) with improved accuracy and resolution when compared with classical simulation and diagnostic techniques. We verified the validity of the adopted methodology in reproducing the blood flow by relying on experimental data. A detailed comparative analysis highlights the differences between healthy and pathological cases in hemodynamic terms. The outcomes of this work contribute to enlarging the knowledge of the blood flow characteristics in the human pulmonary artery, revealing substantial differences between the two clinical scenarios investigated and highlighting how arterial hypertension drastically changes the blood flow. The analysis of the data confirmed the importance of CFD as a supportive tool in understanding, diagnosing, and monitoring the pathophysiological mechanisms underlying cardiovascular diseases, proving to be a powerful means for personalizing surgical treatments. Full article
(This article belongs to the Special Issue Recent Advances in Cardiovascular Flows)
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13 pages, 1725 KiB  
Article
Intra-Cardiac Kinetic Energy and Ventricular Flow Analysis in Bicuspid Aortic Valve: Impact on Left Ventricular Function, Dilation Severity, and Surgical Referral
by Ali Fatehi Hassanabad and Julio Garcia
Fluids 2025, 10(1), 5; https://doi.org/10.3390/fluids10010005 - 27 Dec 2024
Viewed by 442
Abstract
Intra-cardiac kinetic energy (KE) and ventricular flow analysis (VFA), as derived from 4D-flow MRI, can be used to understand the physiological burden placed on the left ventricle (LV) due to bicuspid aortic valve (BAV). Our hypothesis was that the KE of each VFA [...] Read more.
Intra-cardiac kinetic energy (KE) and ventricular flow analysis (VFA), as derived from 4D-flow MRI, can be used to understand the physiological burden placed on the left ventricle (LV) due to bicuspid aortic valve (BAV). Our hypothesis was that the KE of each VFA component would impact the surgical referral outcome depending on LV function decrement, BAV phenotype, and aortic dilation severity. A total of 11 healthy controls and 49 BAV patients were recruited. All subjects underwent cardiac magnetic resonance imaging (MRI) examination. The LV mass was inferior in the controls than in the BAV patients (90 ± 26 g vs. 45 ± 17 g, p = 0.025), as well as the inferior ascending aorta diameter indexed (15.8 ± 2.5 mm/m2 vs. 19.3 ± 3.5 mm/m2, p = 0.005). The VFA KE was higher in the BAV group; significant increments were found for the maximum KE and mean KE in the VFA components (p < 0.05). A total of 14 BAV subjects underwent surgery after the scans. When comparing BAV nonsurgery vs. surgery-referred cohorts, the maximum KE and mean KE were elevated (p < 0.05). The maximum and mean KE were also associated with surgical referral (r = 0.438, p = 0.002 and r = 0.371, p = 0.009, respectively). In conclusion, the KE from VFA components significantly increased in BAV patients, including in BAV patients undergoing surgery. Full article
(This article belongs to the Special Issue Recent Advances in Cardiovascular Flows)
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25 pages, 12323 KiB  
Article
Large-Eddy Simulation of the Flow Past a Circular Cylinder at Re = 130,000: Effects of Numerical Platforms and Single- and Double-Precision Arithmetic
by Dmitry A. Lysenko
Fluids 2025, 10(1), 4; https://doi.org/10.3390/fluids10010004 - 26 Dec 2024
Viewed by 499
Abstract
Numerical simulations of sub-critical flow past a circular cylinder at Reynolds number Re = 130,000 are performed using two numerical platforms: the commercial, Ansys Fluent, and the open-source, OpenFOAM (finite volume method and large-eddy simulation based on a differential equation for the [...] Read more.
Numerical simulations of sub-critical flow past a circular cylinder at Reynolds number Re = 130,000 are performed using two numerical platforms: the commercial, Ansys Fluent, and the open-source, OpenFOAM (finite volume method and large-eddy simulation based on a differential equation for the sub-grid kinetic energy). An overview of the available experimental data and similar large-eddy simulation studies is presented. A detailed analysis of all accumulated data demonstrates satisfactory agreement between them with a dispersion of approximately 20% for the main integral flow parameters. A detailed comparison of the results obtained using single- and double-precision numerical methods in Ansys Fluent did not reveal any noticeable discrepancies in the integral and local flow parameters as well as the spectral characteristics. It is shown that the behavior of the dynamic system of the fluid dynamic equations computed with single precision is stable by Lyapunov and does not lead to any loss of accuracy. The reconstructed attractors of the dynamic systems in phase space are limited by an ellipsoid. Full article
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15 pages, 5849 KiB  
Article
Damage on a Solid–Liquid Interface Induced by the Dynamical Behavior of Injected Gas Bubbles in Flowing Mercury
by Hiroyuki Kogawa, Takashi Wakui and Masatoshi Futakawa
Fluids 2025, 10(1), 3; https://doi.org/10.3390/fluids10010003 - 26 Dec 2024
Viewed by 366
Abstract
Microbubbles have been applied in various fields. In the mercury targets of spallation neutron sources, where cavitation damage is a crucial issue for life estimation, microbubbles are injected into the mercury to absorb the thermal expansion of the mercury caused by the pulsed [...] Read more.
Microbubbles have been applied in various fields. In the mercury targets of spallation neutron sources, where cavitation damage is a crucial issue for life estimation, microbubbles are injected into the mercury to absorb the thermal expansion of the mercury caused by the pulsed proton beam injection and reduce the macroscopic pressure waves, which results in reducing the damage. Recently, when the proton beam power was increased and the number of injected gas bubbles was increased, unique damage morphologies were observed on the solid–liquid interface. Detailed observation and numerical analyses revealed that the microscopic pressure emitted from the gas bubbles contracting is sufficient to form pit damage, i.e., the directions of streak-like defects which are formed by connecting the pit damage coincides with the direction of the gas bubble trajectories, and the distances between the pits was understandable when taking the natural period of gas bubble vibration into account. This indicates that gas microbubbles, used to reduce macroscopic pressure waves, have the potential to be inceptions of cavitation damage due to the microscopic pressure emitted from these gas bubbles. To completely mitigate the damage, we have to consider the two effects of injecting gas bubbles: reducing macroscopic pressure waves and reducing the microscopic pressure due to bubble dynamics. Full article
(This article belongs to the Special Issue Cavitation and Bubble Dynamics)
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20 pages, 5525 KiB  
Article
Rarefied Nozzle Flow Computation Using the Viscosity-Based Direct Simulation Monte Carlo Method
by Deepa Raj Mopuru, Nishanth Dongari and Srihari Payyavula
Fluids 2025, 10(1), 2; https://doi.org/10.3390/fluids10010002 - 24 Dec 2024
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Abstract
Micro-nozzles are essential for enabling precise satellite attitude control and orbital maneuvers. Accurate prediction of performance parameters, including thrust and specific impulse, is critical, necessitating careful design of these nozzles. Given the high Knudsen numbers associated with micro-nozzle flows, rarefied gas dynamics often [...] Read more.
Micro-nozzles are essential for enabling precise satellite attitude control and orbital maneuvers. Accurate prediction of performance parameters, including thrust and specific impulse, is critical, necessitating careful design of these nozzles. Given the high Knudsen numbers associated with micro-nozzle flows, rarefied gas dynamics often dominate, and conventional computational fluid dynamics (CFD) methods fail to capture accurate flow expansion behavior. The Direct Simulation Monte Carlo (DSMC) method, developed by Bird, is widely used for modeling rarefied flows; however, it has been primarily implemented on platforms like OpenFOAM and FORTRAN, with limited exploration in MATLAB. This study presents the development of a viscosity-based DSMC (μDSMC) simulation framework in MATLAB for analyzing rarefied gas expansion through micro-nozzles. Key boundary conditions, including upstream and downstream pressure conditions and thermal wall treatments with diffuse reflection, are incorporated into the code. The μDSMC results are validated against traditional DSMC outcomes, showing strong agreement. Grid convergence studies indicate that the radial grid size must be less than one-third of the mean free path, with a more relaxed requirement on axial grid size. Flow characteristics within micro-nozzles are evaluated across varying ambient pressures and gas species in terms of the back pressure ratio, effective exit flow ratio, and exit flow velocity. Studies indicated that a minimum back pressure ratio is required, beyond which the effective nozzle flow expansion is achieved. Parametric analysis further suggests that gases with lower molecular weights are preferable for achieving optimal expansion in micro-nozzles under low ambient pressures. Full article
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Article
Impact of Addition of a Newtonian Solvent to a Giesekus Fluid: Analytical Determination of Flow Rate in Plane Laminar Motion
by Irene Daprà, Giambattista Scarpi and Vittorio Di Federico
Fluids 2025, 10(1), 1; https://doi.org/10.3390/fluids10010001 - 24 Dec 2024
Viewed by 393
Abstract
In this study, the influence of the presence of a Newtonian solvent on the flow of a Giesekus fluid in a plane channel or fracture is investigated with a focus on the determination of the flow rate for an assigned external pressure gradient. [...] Read more.
In this study, the influence of the presence of a Newtonian solvent on the flow of a Giesekus fluid in a plane channel or fracture is investigated with a focus on the determination of the flow rate for an assigned external pressure gradient. The pressure field is nonlinear due to the presence of the normal transverse stress component. As expected, the flow rate per unit width Q′ is larger than for a Newtonian fluid and decreases as the solvent increases. It is strongly dependent on the viscosity ratio ε (0≤ε≤1), the dimensionless mobility parameter β (0≤β≤1) and the Deborah number De, the dimensionless driving pressure gradient. The degree of dependency is notably strong in the low range of ε. Furthermore, Q′ increases with De and tends to a constant asymptotic value for large De, subject to the limitation of laminar flow. When the mobility factor β is in the range 0.5÷1, there is a minimum value of ε  to obtain an assigned value of De. The ratio UN/U between Newtonian and actual mean velocity depends only on the product βDe, as for other non-Newtonian fluids. Full article
(This article belongs to the Special Issue Advances in Computational Mechanics of Non-Newtonian Fluids)
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