Fluids

21 pages, 2488 KiB

Open AccessArticle

Combination of Integral Transforms and Linear Optimization for Source Reconstruction in Heat and Mass Diffusion Problems

by André J. P. de Oliveira, Diego C. Knupp, Luiz A. S. Abreu, David A. Pelta and Antônio J. da Silva Neto

Fluids 2025, 10(4), 106; https://doi.org/10.3390/fluids10040106 - 21 Apr 2025

Viewed by 104

Abstract

This paper presents a novel methodology for estimating space- and time-dependent source terms in heat and mass diffusion problems. The approach combines classical integral transform techniques (CITTs) with the least squares optimization method, enabling an efficient reconstruction of source terms. The method employs [...] Read more.

This paper presents a novel methodology for estimating space- and time-dependent source terms in heat and mass diffusion problems. The approach combines classical integral transform techniques (CITTs) with the least squares optimization method, enabling an efficient reconstruction of source terms. The method employs a double expansion framework, using both spatial eigenfunction and temporal expansions. The new presented idea assumes that the source term can be expressed as a spatial expansion in eigenfunctions of the eigenvalue problem, and then each transient function associated with each term of spatial expansion is rewritten as an additional expansion, where the unknown coefficients approximating the transformed source enable the direct use of the solution in the objective function. This, in turn, results in a linear optimization problem that can be quickly minimized. Numerical experiments, including one-dimensional and two-dimensional scenarios, demonstrate the accuracy of the proposed method in the presence of noisy data. The results highlight the method’s robustness and computational efficiency, even with minimal temporal expansion terms. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics Applied to Transport Phenomena)

► Show Figures

Figure 1

25 pages, 8015 KiB

Open AccessArticle

Fluid–Structure Coupling Analysis of the Vibration Characteristics of a High-Parameter Spool

by Haozhe Jin, Haotian Xu, Jiongming Zhang, Chao Wang and Xiaofei Liu

Fluids 2025, 10(4), 105; https://doi.org/10.3390/fluids10040105 - 21 Apr 2025

Viewed by 176

Abstract

High-performance control valves are essential components in power plants. High-parameter control valves are specialized valves for controlling high-pressure, high-flow, high-temperature, and highly corrosive media. Control valve performance is critical for the stable operation of power plants. The multi-stage counter-flow passage is a common [...] Read more.

High-performance control valves are essential components in power plants. High-parameter control valves are specialized valves for controlling high-pressure, high-flow, high-temperature, and highly corrosive media. Control valve performance is critical for the stable operation of power plants. The multi-stage counter-flow passage is a common structure in pressure-reducing control valves, effectively mitigating cavitation and erosion on the valve walls. However, in practice, vibration issues in multi-stage passage valves are particularly pronounced. This study employs FSI (fluid–structure interaction) to simulate the vibration characteristics of multi-stage passages. Flow field data for the multi-stage passage are obtained through FLUENT software. A time-frequency analysis of the lift coefficient in the multi-stage passage flow field was performed. The vibration characteristics of the valve core’s inlet and outlet surfaces were studied using Transient Structural software. The results show that when high-pressure fluid passes through the valve core’s passage, it undergoes buffering, steering, and rotating motions, leading to a gradual pressure drop and generating resistance and lift. These phenomena are primarily caused by vortex shedding in the flow field, with the dominant frequency observed to be approximately 5400 Hz. Additionally, as the valve core progresses through the P1 phase at the inlet and the P2 phase at the outlet, the vibration intensity gradually decreases, reaching a minimum in the sixth phase, before increasing and peaking in the final stage. Analysis of the flow field characteristics within the valve core passage reveals the significant impact of vortex shedding on the valve core’s vibration and lift. Phase analysis of the valve core’s vibration intensity further clarifies its behavioral changes at different operational stages. These findings help optimize the design of multi-stage buffering valve cores, improving their performance and stability. Full article

► Show Figures

Figure 1

19 pages, 6051 KiB

Open AccessArticle

Effect of Deformable Gurney Flaps on the Output Power of Flapping Turbine

by Chebana Abdelbasset, Ghelani Laala, Mohamed Taher Bouzaher, Charaf Eddine Bensaci, Alaeddine Zereg, Nadhir Lebaal and Mounir Aksas

Fluids 2025, 10(4), 104; https://doi.org/10.3390/fluids10040104 - 19 Apr 2025

Viewed by 112

Abstract

The Gurney flap (GF) is a simple flat plate frequently mounted at the airfoil rear. Several investigations have been devoted to studying the effect of a rigid or even movable GF on the aerodynamic behavior of several devices such as flapping airfoils and [...] Read more.

The Gurney flap (GF) is a simple flat plate frequently mounted at the airfoil rear. Several investigations have been devoted to studying the effect of a rigid or even movable GF on the aerodynamic behavior of several devices such as flapping airfoils and vertical or horizontal axis turbines. The present paper proposes a new concept of a deformable Gurney flap (DGF) to improve the output power of a flapping airfoil in vertical mode. The advantage of this model is the full control of the effect on the GF during the flapping movement. The DGF is expandable and contractible which allows for monitoring and adjusting the pressure distribution at the appropriate time and position. By using a 2D transient simulation with a specific dynamic mesh design, an extended numerical analysis has been provided. It was found that this model is able to increase the output power by 19.5%. Furthermore, the concept of the DGF is applied on flapping turbines in hybrid modes such as swing arm mode and D-shaped mode. These modes are investigated to clarify the studied model’s advantage and to demonstrate the possibility of applying this strategy to control the different flapping movements. Full article

► Show Figures

Figure 1

6 pages, 204 KiB

Open AccessCorrection

Correction: Yusuf et al. Magneto-Bioconvection Flow of Williamson Nanofluid over an Inclined Plate with Gyrotactic Microorganisms and Entropy Generation. Fluids 2021, 6, 109

by Tunde A. Yusuf, Fazle Mabood, B. C. Prasannakumara and Ioannis E. Sarris

Fluids 2025, 10(4), 103; https://doi.org/10.3390/fluids10040103 - 17 Apr 2025

Viewed by 89

Abstract

This is an erratum to our published paper Reference [...] Full article

23 pages, 6274 KiB

Open AccessArticle

Thermal Irreversibility in Nano-Enhanced Phase Change Material Liquefaction

by Fikret Alić

Fluids 2025, 10(4), 102; https://doi.org/10.3390/fluids10040102 - 16 Apr 2025

Viewed by 182

Abstract

Inside a closed, thin-walled hollow cylinder, there is a solid state of phase change material (NePCM) that has been nano-enhanced. This NePCM is heated at its bottom, with nanoparticles (Al₂O₃) inserted and homogenized within the PCM (sodium acetate trihydrate, [...] Read more.

Inside a closed, thin-walled hollow cylinder, there is a solid state of phase change material (NePCM) that has been nano-enhanced. This NePCM is heated at its bottom, with nanoparticles (Al₂O₃) inserted and homogenized within the PCM (sodium acetate trihydrate, C₂H₃O₂Na) to create the NePCM. The hollow cylinder is thermally insulated from the outside ambient temperature, while the heat supplied is sufficient to cause a phase change. Once the entire NePCM has converted from a solid to a liquid due to heating, it is then cooled, and the thermal insulation is removed. The cylindrical liquefied NePCM bar is cooled in this manner. Thermal entropy, entransy dissipation rate, and bar efficiency during the heating and cooling of the NePCM bar were analyzed by changing variables. The volume fraction ratio of nanoparticles, inlet heat flux, and liquefied bar height were the variables considered. The results indicate a significant impact on the NePCM bar during liquefaction and convective cooling when the values of these variables are altered. For instance, with an increase in the volume fraction ratio from 3% to 9%, at a constant heat flux of 10⁴ Wm⁻² and a liquefied bar height of 0.02 m, the NePCM bar efficiency decreases to 99%. The thermal entropy from heat conduction through the liquefied NePCM bar is significantly lower compared to the thermal entropy from convective air cooling on its surface. The thermal entropy of the liquefied NePCM bar increases on average by 110% without any cooling. With a volume fraction ratio of 6%, there is an 80% increase in heat flux as the bar height increases to 0.02 m. Full article

(This article belongs to the Section Heat and Mass Transfer)

► Show Figures

Figure 1

19 pages, 7654 KiB

Open AccessArticle

An Improved Regularization Scheme for an Extended Lattice Boltzmann Model

by Zhihong Zhang, Yijin Li and Haobu Gao

Fluids 2025, 10(4), 101; https://doi.org/10.3390/fluids10040101 - 11 Apr 2025

Viewed by 198

Abstract

For an extended lattice Boltzmann model based on a product-form equilibrium distribution function, an improved regularization model with enhanced numerical stability is proposed. In this paper’s regularized collision model, coefficients are calculated using two distinct methods during the reconstruction of the non-equilibrium distribution. [...] Read more.

For an extended lattice Boltzmann model based on a product-form equilibrium distribution function, an improved regularization model with enhanced numerical stability is proposed. In this paper’s regularized collision model, coefficients are calculated using two distinct methods during the reconstruction of the non-equilibrium distribution. The first method stems from the direct projection of the non-equilibrium distribution, while the second method relies on the regularization step, which is refined through the recursive calculation of the coefficients of non-equilibrium Hermite polynomials. Compared to the original lattice Boltzmann model, the recursive regularization method significantly enhances the stability of the numerical scheme by appropriately filtering out second-order and/or higher-order non-hydrodynamic contributions. Initially, under isothermal conditions, the periodic double-shear layer simulations are conducted at Reynolds numbers ranging from 10⁴ to 10⁶, testing the enhanced effect of the regularized model in broadening its available speed range. Subsequently, with a fixed Reynolds number, simulations are performed at various temperature values to assess the model’s performance when deviating from the lattice reference temperature. The results demonstrate that, compared to the original model, the recursive regularization model exhibits improved stability and widens the model’s usable speed and temperature ranges. Full article

► Show Figures

Figure 1

28 pages, 957 KiB

Open AccessArticle

Stability Analysis of Unsteady Laminar Boundary Layers Subject to Streamwise Pressure Gradient

by Miguel Ramirez and Guillermo Araya

Fluids 2025, 10(4), 100; https://doi.org/10.3390/fluids10040100 - 8 Apr 2025

Viewed by 197

Abstract

A transient stability flow analysis is performed using the unsteady laminar boundary layer equations. The flow dynamics are studied via the Navier–Stokes equations. In the case of external spatially developing flow, the differential equations are reduced via Prandtl or boundary-layer assumptions, consisting of [...] Read more.

A transient stability flow analysis is performed using the unsteady laminar boundary layer equations. The flow dynamics are studied via the Navier–Stokes equations. In the case of external spatially developing flow, the differential equations are reduced via Prandtl or boundary-layer assumptions, consisting of continuity and momentum conservation equations. Prescription of streamwise pressure gradients (decelerating and accelerating flows) is carried out by an impulsively started Falkner–Skan (FS) or wedge-flow similarity flow solution in the case of flat plate or a Blasius solution for particular zero-pressure gradient case. The obtained mean streamwise velocity and its derivatives from FS flows are then inserted into the well-known Orr–Sommerfeld equation of small disturbances at different dimensionless times (

τ

). Finally, the corresponding eigenvalues are dynamically computed for temporal stability analysis. A finite difference algorithm is effectively applied to solve the Orr–Sommerfeld equations. It is observed that flow acceleration or favorable pressure gradients (FPGs) lead to a significantly shorter transient period before reaching steady-state conditions, as the developed shear layer is notably thinner compared to cases with adverse pressure gradients (APGs). During the transient phase (i.e., for

τ < 1

), the majority of the flow modifications are confined to the innermost 20–25% of the boundary layer, in proximity to the wall. In the context of temporal flow stability, the magnitude of the pressure gradient is pivotal in determining the streamwise extent of the Tollmien–Schlichting (TS) waves. In highly accelerated laminar flows, these waves experience considerable elongation. Conversely, under the influence of a strong adverse pressure gradient, the characteristic streamwise length of the smallest unstable wavelength, which is necessary for destabilization via TS waves, is significantly reduced. Furthermore, flows subjected to acceleration (

β

> 0) exhibit a higher propensity to transition towards a more stable state during the initial transient phase. For instance, the time response required to reach the steady-state critical Reynolds number was approximately 1

τ

for

β

= 0.18 (FPG) and

τ

= 6.8 for

β

= −0.18 (APG). Full article

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

► Show Figures

Figure 1

29 pages, 12104 KiB

Open AccessFeature PaperArticle

Numerical Investigations of the Influence of the Spool Structure on the Flow and Damage Characteristics of Control Valves

by Haozhe Jin, Haokun An, Chao Wang and Xiaofei Liu

Fluids 2025, 10(4), 99; https://doi.org/10.3390/fluids10040099 - 7 Apr 2025

Viewed by 156

Abstract

This study investigates the flow dynamics and damage characteristics of liquid level control valves in direct coal liquefaction processes. The primary failure mechanisms are identified as eccentric jet-induced unilateral wall damage, cavitation erosion, and solid particle erosive wear. A numerical simulation framework was [...] Read more.

This study investigates the flow dynamics and damage characteristics of liquid level control valves in direct coal liquefaction processes. The primary failure mechanisms are identified as eccentric jet-induced unilateral wall damage, cavitation erosion, and solid particle erosive wear. A numerical simulation framework was developed to analyze the effects of varying spool angles (72°, 90°, 98°, 105°, and 120°) on flow stability, cavitation dynamics, and erosion patterns. The key findings include the following: A spool angle of 90° achieves the most uniform pressure distribution and minimizes eccentric jet phenomena. Spool geometry modifications exhibit a negligible influence on cavitation characteristics. Reduced wear rates are observed at smaller spool angles (72° and 90°), with the lowest particle-induced erosion occurring at 90°. There is a certain correlation between the particle residence time and the wear of the valve core wall, which is illustrated in the shorter residence times that are correlated with accelerated material degradation. The optimal spool angle of 90° simultaneously mitigates eccentric jet effects, cavitation, and erosive wear. This research provides novel insights for predictive failure analysis and the structural optimization of control valves in high-pressure multi-phase flow systems. Full article

(This article belongs to the Special Issue Flow Control Techniques: Advances in Flow System Analysis, Modeling and Applications)

► Show Figures

Figure 1

15 pages, 3456 KiB

Open AccessArticle

Evaluation of the Adsorption Potential of Benzo(a)pyrene in Coal Produced from Sewage Treatment Station Sludge

by Natiele Kleemann, Débora Jaeschke, Nauro Silveira, Jr., Luiz Pinto, Tito Cadaval, Jr., Jean Arias, Sergiane Barbosa, Ednei Primel and Adilson Bamberg

Fluids 2025, 10(4), 98; https://doi.org/10.3390/fluids10040098 - 7 Apr 2025

Viewed by 213

Abstract

This work investigates the adsorption of benzo[a]pyrene (BaP) using a charcoal adsorbent derived from sewage treatment plant sludge. BaP is a polycyclic aromatic hydrocarbon (PAH), carcinogenic to humans, which his used by the World Health Organization as a marker for all PAH mixtures. [...] Read more.

This work investigates the adsorption of benzo[a]pyrene (BaP) using a charcoal adsorbent derived from sewage treatment plant sludge. BaP is a polycyclic aromatic hydrocarbon (PAH), carcinogenic to humans, which his used by the World Health Organization as a marker for all PAH mixtures. The charcoal was produced by the pyrolysis (500 °C, 4 h) of municipal sewage sludge. The resulting biochar presented mesoporous and oxygenated functional groups that are beneficial for the adsorption of benzo[a]pyrene. The material contained graphitic structures, suggesting potential sites for π–π interactions. The adsorption followed the Elovich kinetic model. A maximum adsorbed value of 60.8 µg g⁻¹ was achieved for an initial BaP concentration of 100 µg L⁻¹ of BaP at 298 K after 20 min. Parameters related to mass transfer phenomena, such as the intraparticle diffusion coefficient, were determined using the homogeneous solid diffusion model (HSDM). These experimental data demonstrate the great potential for computational fluid dynamics (CFD) applications. The value reached for the intraparticle diffusion coefficient was 1.63 × 10⁻¹³ m²s⁻¹. Adsorption equilibrium experiments showed that the Langmuir model was most suitable for experimental data, suggesting a monolayer molecular adsorption process. The results showed that charcoal can be employed as an effective material for removing BaP. Full article

(This article belongs to the Special Issue Computational Fluid Dynamics Applied to Transport Phenomena)

► Show Figures

Figure 1

21 pages, 9514 KiB

Open AccessArticle

Choked Flow in Calibrated Orifices for Hydraulic Fluid Power Applications

by Massimo Rundo, Paola Fresia, Carmine Conte and Paolo Casoli

Fluids 2025, 10(4), 97; https://doi.org/10.3390/fluids10040097 - 6 Apr 2025

Viewed by 270

Abstract

The flow rate through hydraulic resistance increases with the pressure drop across it, but this correlation is no longer valid under cavitation conditions. This study investigates choked flow in calibrated screw-in orifices, widely used for control and damping in fluid power components. An [...] Read more.

The flow rate through hydraulic resistance increases with the pressure drop across it, but this correlation is no longer valid under cavitation conditions. This study investigates choked flow in calibrated screw-in orifices, widely used for control and damping in fluid power components. An experimental campaign was conducted on orifices with diameters ranging from 1 to 0.4 mm at various upstream pressures using hydraulic oil. A computational fluid dynamics (CFD) model was developed and validated against experiments, then used to analyze the effects of geometric parameters such as edge chamfers, hex wrench sockets, and length-to-diameter ratio. From CFD results, an analytical correlation between flow rate and pressure drop was derived, incorporating flow saturation effects. The study revealed that under saturation conditions, flow rate is largely unaffected by geometry, except for the ideal case of a perfectly sharp-edged orifice, which is rarely encountered. Even minimal chamfers of a few hundredths of a millimeter make the restrictor non-ideal. The derived correlation can be integrated into lumped parameter models of fluid power components to account for choked flow. Full article

(This article belongs to the Special Issue Multiphase Flow and Fluid Machinery)

► Show Figures

Figure 1

17 pages, 4769 KiB

Open AccessArticle

CFD Analysis of Hydrodynamic Loads on Jack-Up Platforms Using Buoyancy-Modified k-ω SST Turbulence Model

by Nu Rhahida Arini, Gilang Muhammad, Eko Charnius Ilman, Teguh Hady Ariwibowo, Mohamed Moshrefi-Torbati and Deni Saputra

Fluids 2025, 10(4), 96; https://doi.org/10.3390/fluids10040096 - 4 Apr 2025

Viewed by 302

Abstract

The offshore jack-up production platform operates in extreme and unpredictable marine environments. Therefore, its structural strength must be designed to withstand harsh conditions, particularly hydrodynamic loads from waves and ocean currents. This study aims to numerically analyze the interaction of marine hydrodynamic forces [...] Read more.

The offshore jack-up production platform operates in extreme and unpredictable marine environments. Therefore, its structural strength must be designed to withstand harsh conditions, particularly hydrodynamic loads from waves and ocean currents. This study aims to numerically analyze the interaction of marine hydrodynamic forces with a jack-up production platform using OpenFOAM v1606, a Computational Fluid Dynamics (CFD) software. Specifically, the research evaluates a buoyancy-modified k−ω SST turbulence model based on the Standard Gradient Diffusion Hypothesis (SGDH) on a 3D jack-up platform model. The analysis is conducted using a Stokes 5th-order wave model within the waves2Foam toolbox, considering four variations in wave height and period. The results demonstrate that the modified turbulence model provides more accurate predictions. Additionally, they reveal that the forces acting on the platform’s walls are directly proportional to wave height and period, with the highest recorded load reaching 4000 N in Case A, where the wave height and period are 5.4 m and 5.9 s, respectively. Furthermore, it is observed that most of the forces exerted on the platform hull are vertical, primarily due to the negative pressure on the platform’s bottom side. Full article

(This article belongs to the Special Issue Marine Hydrodynamics: Theory and Application)

► Show Figures

Figure 1

19 pages, 2153 KiB

Open AccessArticle

Complex Network Method for Inferring Well Interconnectivity in Hydrocarbon Reservoirs

by M. Mayoral-Villa, F. A. Godínez, J. A. González-Guevara, J. Klapp and J. E. V. Guzmán

Fluids 2025, 10(4), 95; https://doi.org/10.3390/fluids10040095 - 4 Apr 2025

Viewed by 206

Abstract

Reservoir management becomes increasingly critical as fields decline to a fully mature state. During this stage, engineers and managers must make decisions based on a limited set of field measurements (such as pressure and production rates). At the same time, up-to-date information concerning [...] Read more.

Reservoir management becomes increasingly critical as fields decline to a fully mature state. During this stage, engineers and managers must make decisions based on a limited set of field measurements (such as pressure and production rates). At the same time, up-to-date information concerning the reservoir’s geophysical characteristics and petrochemical properties may be unavailable. To aid in the expert’s appraisal of this production scenario, we present the results of applying a data-driven methodology based on visibility graph analysis (VGA) and multiplex visibility graphs (MVGs). It infers inter-well connectivities at the reservoir level and clarifies the degrees of mutual influence among wells. This parameter-free technique supersedes the limitations of traditional methods, such as the capacitance–resistance (CR) models and inter-well numerical simulation models (INSIMs) that rely heavily on geophysical data and are sensitive to porous datasets. We tested the method with actual data representing a field’s state over 62 years. The technique revealed short- and long-term dependencies between wells when applied to historical records of production rates (oil, water, and gas) and pressures (bottom and wellhead). The inferred connectivity aligned with documented operational trends and successfully identified stable connectivity structures. In addition, the interlayer mutual information (IMI) parameter exceeded 0.75 in most periods, confirming high temporal consistency. Moreover, validation by field experts confirmed that the inferred interconnectivity was consistent with the observed production. Full article

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

► Show Figures

Figure 1

15 pages, 2793 KiB

Open AccessReview

Geometric Analyses of the Expiratory Flow–Volume Curve to Identify Expiratory Flow Limitation During Exercise

by Hans Haverkamp, Gregory Petrics and Yannick Molgat-Seon

Fluids 2025, 10(4), 94; https://doi.org/10.3390/fluids10040094 - 3 Apr 2025

Viewed by 289

Abstract

An important purpose of cardiopulmonary exercise testing (CPET) is to query the mechanisms for unexplained shortness of breath or exaggerated exertional dyspnea. Expiratory flow limitation (EFL) is an important indicator of ventilatory constraint that can negatively influence both dyspnea and exercise capacity. Unfortunately, [...] Read more.

An important purpose of cardiopulmonary exercise testing (CPET) is to query the mechanisms for unexplained shortness of breath or exaggerated exertional dyspnea. Expiratory flow limitation (EFL) is an important indicator of ventilatory constraint that can negatively influence both dyspnea and exercise capacity. Unfortunately, due to logistical challenges and lack of sufficient clinical training, EFL is rarely measured during CPET. The conventional method for identifying exercise EFL is limited because it requires patient cooperation and it is also dependent on the maximal expiratory flow–volume curve, which underestimates actual maximal expiratory flow during exercise. Simplified methods for identifying EFL that are based on the shape of the exercise tidal flow–volume curve would improve the accessibility of measuring EFL during exercise. The overall aim of this review is to critically review the approaches and methods used to measure EFL in exercising adults. We review the physiology underlying EFL and the conventional methods for determining exercise EFL. We then provide critical analyses of more recent methods for identifying exercise EFL that are based on the geometry of the exercise tidal expiratory flow–volume curve. Finally, we highlight recent work designed to assess exercise EFL using a type of deep machine learning known as a convolutional neural network. Full article

(This article belongs to the Special Issue Respiratory Flows)

► Show Figures

Figure 1

34 pages, 3644 KiB

Open AccessReview

A Review of Diffuse Interface-Capturing Methods for Compressible Multiphase Flows

by Ebenezer Mayowa Adebayo, Panagiotis Tsoutsanis and Karl W. Jenkins

Fluids 2025, 10(4), 93; https://doi.org/10.3390/fluids10040093 - 3 Apr 2025

Viewed by 216

Abstract

This paper discusses in detail the classification, historical development, and application of diffuse interface-capturing models (DIMs) for compressible multiphase flows. The work begins with an overview of the development of DIMs, highlighting important contributions and key moments from classical studies to contemporary advances. [...] Read more.

This paper discusses in detail the classification, historical development, and application of diffuse interface-capturing models (DIMs) for compressible multiphase flows. The work begins with an overview of the development of DIMs, highlighting important contributions and key moments from classical studies to contemporary advances. The theoretical foundations and computational methods of the diffuse interface method are outlined for the full models and the reduced models or sub-models. Some of the difficulties encountered when using DIMs for multiphase flow modelling are also discussed. Full article

(This article belongs to the Special Issue Compressible Flows)

► Show Figures

Figure 1

17 pages, 1224 KiB

Open AccessArticle

Numerical Approximation of the In Situ Combustion Model Using the Nonlinear Mixed Complementarity Method

by Julio César Agustin Sangay, Alexis Rodriguez Carranza, Juan Carlos Ponte Bejarano, José Luis Ponte Bejarano, Eddy Cristiam Miranda Ramos, Obidio Rubio and Franco Rubio-López

Fluids 2025, 10(4), 92; https://doi.org/10.3390/fluids10040092 - 3 Apr 2025

Viewed by 192

Abstract

In this work, we study a numerical method to approximate the exact solution of a simple in situ combustion model. To achieve this, we use the mixed nonlinear complementarity method (MNCP), a variation of the Newton method for solving nonlinear systems, incorporating a [...] Read more.

In this work, we study a numerical method to approximate the exact solution of a simple in situ combustion model. To achieve this, we use the mixed nonlinear complementarity method (MNCP), a variation of the Newton method for solving nonlinear systems, incorporating a single Hadamard product in its formulation. The method is based on an implicit finite difference scheme and a mixed nonlinear complementarity algorithm (FDA-MNCP). One of its main advantages is that it ensures global convergence, unlike the finite difference method and the Newton method, which only guarantee local convergence. We apply this theory to an in situ combustion model, reformulating it in terms of mixed complementarity. Additionally, we compare it with the FDA-NCP method, demonstrating that the FDA-MNCP is computationally more efficient when the spatial discretization is refined. Full article

► Show Figures

Figure 1

20 pages, 9841 KiB

Open AccessArticle

Experimental Investigations of Capillary Flow in Three-Dimensional-Printed Microchannels

by Behrouz Pirouz, Seyed Navid Naghib, Diamante Chirillo, Hana Javadi Nejad and Patrizia Piro

Fluids 2025, 10(4), 91; https://doi.org/10.3390/fluids10040091 - 2 Apr 2025

Viewed by 239

Abstract

In recent years, the application of microfluidic devices has increased, and three-dimensional (3D) printers for fabricating microdevices could be considered a suitable technique but, in some cases, may confront some issues. The main issues include channel roughness values, print orientation due to the [...] Read more.

In recent years, the application of microfluidic devices has increased, and three-dimensional (3D) printers for fabricating microdevices could be considered a suitable technique but, in some cases, may confront some issues. The main issues include channel roughness values, print orientation due to the 3D printer’s setup, filament materials, nozzle specifications, and condition. This study aims to analyze the capillary-driven flow in microdevices produced by 3D printers. Therefore, four 3D printer-based microchannels were investigated, and the capillary-driven flow of five liquids with different viscosities and contact angles was evaluated experimentally. The experimental results were compared with theoretical calculations using the Lucas−Washburn equation, and the impact of the width, length, and closed and open microchannel on flow behaviors was explored. The experimental results showed that the peak velocity for open and closed microchannels decreases with the length. Moreover, there were differences in flow behavior between open and closed microchannels. For the former, the maximum average velocity appeared in the microchannel with a width of 400 μm, while for the latter, it was for a width of 1000 μm. In addition, the flow velocity decreased when the viscosity increased, regardless of microchannel width. The decrease was more pronounced for the lower-viscosity liquids (ethanol and water) and smaller for the higher-viscosity ones (coffee and olive oil). Finally, the advantages and challenges of 3D printer-based microdevices are presented. Full article

► Show Figures

Figure 1

30 pages, 26544 KiB

Open AccessArticle

Pseudopotential Lattice Boltzmann Method Simulation of Boiling Heat Transfer at Different Reduced Temperatures

by Matheus dos Santos Guzella and Luben Cabezas-Gómez

Fluids 2025, 10(4), 90; https://doi.org/10.3390/fluids10040090 - 1 Apr 2025

Viewed by 213

Abstract

Boiling heat transfer plays a crucial role in various engineering applications, requiring accurate numerical modeling to capture phase-change dynamics. This study employs the pseudopotential lattice Boltzmann method (LBM) to simulate boiling heat transfer at different reduced temperatures, aiming to provide deeper insights into [...] Read more.

Boiling heat transfer plays a crucial role in various engineering applications, requiring accurate numerical modeling to capture phase-change dynamics. This study employs the pseudopotential lattice Boltzmann method (LBM) to simulate boiling heat transfer at different reduced temperatures, aiming to provide deeper insights into bubble dynamics and heat transfer mechanisms. The LBM framework incorporates a multi-relaxation-time approach and the Peng–Robinson equation of state to enhance numerical stability and thermodynamic consistency. Simulations were performed to analyze bubble nucleation, growth, and detachment across varying reduced temperatures, considering the influence of surface wettability, surface tension and gravitational acceleration. The results indicate a strong dependence of bubble behavior on the reduced temperature, affecting both heat flux and boiling regimes. The numerical findings show reasonable agreement with theoretical predictions and experimental trends, validating the effectiveness of the LBM approach for phase-change simulations. Additionally, this study highlights the role of contact angle variation in modifying boiling characteristics, emphasizing the necessity of accurate surface interaction modeling. The outcomes of this work contribute to advancing computational methodologies for boiling heat transfer, supporting improved thermal management in industrial applications. Full article

(This article belongs to the Special Issue Lattice Boltzmann Methods: Fundamentals and Applications)

► Show Figures

Figure 1

17 pages, 4847 KiB

Open AccessArticle

Ultrasonic Atomization—From Onset of Protruding Free Surface to Emanating Beads Fountain—Leading to Mist Spreading

by Katsumi Tsuchiya and Xiaolu Wang

Fluids 2025, 10(4), 89; https://doi.org/10.3390/fluids10040089 - 1 Apr 2025

Viewed by 200

Abstract

The process of ultrasonic atomization involves a series of dynamic/topological deformations of free surface, though not always, of a bulk liquid (initially) below the air. This study focuses on such dynamic interfacial alterations realized by changing some acousto-related operating conditions, including ultrasound excitation [...] Read more.

The process of ultrasonic atomization involves a series of dynamic/topological deformations of free surface, though not always, of a bulk liquid (initially) below the air. This study focuses on such dynamic interfacial alterations realized by changing some acousto-related operating conditions, including ultrasound excitation frequency, acoustic strength or input power density, and the presence/absence of a “stabilizing” nozzle. High-speed, high-resolution imaging made it possible to qualitatively identify four representative transitions/demarcations: (1) the onset of a protrusion on otherwise flat free surface; (2) the appearance of undulation along the growing protuberance; (3) the triggering of emanating beads fountain out of this foundation-like region; and (4) the induction of droplets bursting and/or mist spreading. Quantitatively examined were the two-parameters specifications—on the degrees as well as induction—of the periodicity in the protrusion-surface and beads-fountain oscillations, detected over wider ranges of driving/excitation frequency (0.43–3.0 MHz) and input power density (0.5–10 W/

{c m}^{2}

) applied to the ultrasound transducer of flat surface on which the nozzle was either mounted or not. The resulting time sequence of images processed for the extended operating ranges, regarding the fountain structure pertaining, in particular, to recurring beads, confirms the wave-associated nature, i.e., their size “scalability” to the ultrasound wavelength, predictable from the traveling wave relationship. The thresholds in acoustic conditions for each of the four transition states of the fountain structure have been identified—notably, the onset of plausible “bifurcation” in the chain-beads’ diameter below a critical excitation frequency. Full article

(This article belongs to the Special Issue Advances in Multiphase Flow Science and Technology, 2nd Edition)

► Show Figures

Graphical abstract

45 pages, 27925 KiB

Open AccessReview

Recent Advancements in Fish-on-Chip: A Comprehensive Review

by Tushar Nath and Hua Tan

Fluids 2025, 10(4), 88; https://doi.org/10.3390/fluids10040088 - 31 Mar 2025

Viewed by 650

Abstract

Zebrafish (Danio rerio) emerged as a suitable vertebrate model organism in the 1960s, owing to its transparent embryos and ease of breeding. Research utilizing zebrafish as a model organism gained significant momentum in the 1970s, particularly in the field of developmental [...] Read more.

Zebrafish (Danio rerio) emerged as a suitable vertebrate model organism in the 1960s, owing to its transparent embryos and ease of breeding. Research utilizing zebrafish as a model organism gained significant momentum in the 1970s, particularly in the field of developmental biology. Over the years, zebrafish has become an indispensable model across various domains of biological research. However, conventional techniques for handling zebrafish in research settings have been limited by challenges related to survival rates, throughput, and imaging capabilities. The advancements in microfluidics and Micro-Electro-Mechanical Systems (MEMS) technology have addressed many of these challenges, enabling significant progress in zebrafish-based studies. The integration of microchannels, which ensure laminar flow for precise liquid handling, alongside microsensors and actuators for trapping mechanisms and high-resolution imaging, has greatly enhanced experimental efficiency and precision. This review provides a comprehensive analysis of very recent advancements in Fish-on-Chip (FOC) technologies, with a focus on their applications in zebrafish research, including trapping, imaging, transportation, and studies involving drug screening and disease modeling. Furthermore, we discuss recent efforts in retaining progressively motile zebrafish sperm, which is increasingly critical to meeting the rising demand for diverse zebrafish lines. Finally, we discuss an automated microfluidic-based fish farm developed using these technologies and conclude the review by highlighting potential future directions for Fish-on-Chip (FOC) technology. Full article

► Show Figures

Figure 1

17 pages, 3125 KiB

Open AccessArticle

Structural Optimization of the Venturi Fertilizer Applicator Using Head Loss Calculation Methods

by Zhiyang Zhang, Yang Li, Juling Gao, Pan Tang and Feng Huang

Fluids 2025, 10(4), 87; https://doi.org/10.3390/fluids10040087 - 31 Mar 2025

Viewed by 220

Abstract

Fertilizer suction flow rate is an important performance parameter of the Venturi fertilizer applicator. This study aims to analyze the optimal structure of the Venturi fertilizer applicator with the goal of maximizing the suction flow rate at the same inlet and outlet pressures. [...] Read more.

Fertilizer suction flow rate is an important performance parameter of the Venturi fertilizer applicator. This study aims to analyze the optimal structure of the Venturi fertilizer applicator with the goal of maximizing the suction flow rate at the same inlet and outlet pressures. A Venturi tube was used as a simplified case for investigating the Venturi injector. A calculation formula for the head loss between the inlet and outlet of the Venturi tube was derived based on the Bernoulli equation and the Darcy–Weisbach formula. Subsequently, it was modified through regression analysis based on the experimental and numerical simulation results of the flow on the Venturi tube. The optimal structure of the Venturi injector was further analyzed based on the head loss calculation formula. The optimal range for the reducing angle and expanding angle of the Venturi injector were determined to be 20–28° and 6–10°, respectively. The optimal throat diameter was identified to be 5–7 mm when the inlet flow rates were within the range of 1.5–2.5 m³/h. The optimum suction pipe diameter and throat pipe length were both equal to the throat diameter. Full article

(This article belongs to the Special Issue Hydraulic Flow in Pipelines)

► Show Figures

Figure 1

13 pages, 1565 KiB

Open AccessReview

Volume Kinetic Analysis in Living Humans: Background History and Answers to 15 Questions in Physiology and Medicine

by Robert G. Hahn

Fluids 2025, 10(4), 86; https://doi.org/10.3390/fluids10040086 - 28 Mar 2025

Viewed by 257

Abstract

Volume kinetics is a pharmacokinetic method for analysis of the distribution and elimination of infusion fluids. The approach has primarily been used to improve the planning of fluid therapy during surgery but is also useful for answering physiological questions. The kinetics is based [...] Read more.

Volume kinetics is a pharmacokinetic method for analysis of the distribution and elimination of infusion fluids. The approach has primarily been used to improve the planning of fluid therapy during surgery but is also useful for answering physiological questions. The kinetics is based on 15–35 serial measurements of the blood hemoglobin concentration during and after the fluid is administered intravenously. Crystalloid fluid, such as isotonic saline and Ringer’s lactate, distributes between three compartments that are filled in succession depending on how much fluid is administered. The equilibration of fluid between these three compartments is governed by five rate constants. The compartments are the plasma (V_c), and a fast-exchange (V_t1) and a slow-exchange interstitial compartment (V_t2). The last compartment operates like an overflow reservoir and, if filled, markedly, prolongs the half-life of the fluid. By contrast, the volume of a colloid fluid distributes in a single compartment (V_c) from where the expansion is reduced by capillary leakage and urinary excretion. This review gives 15 examples of physiological or medical questions where volume kinetics has provided answers. These include why urine flow is low during general anesthesia, the inhibitory effects of anesthetics on lymphatic pumping, the influence of dopamine and phenylephrine on urine output, fluid maldistribution in pre-eclampsia, plasma volume oscillations, and issues related to the endothelial glycocalyx layer. Full article

(This article belongs to the Special Issue Biological Fluid Dynamics, 2nd Edition)

► Show Figures

Figure 1

25 pages, 6488 KiB

Open AccessArticle

High y⁺ Shear-Stress Turbulence Implementation for High Flux Isotope Reactor Narrow Channel Flows

by Emilian Popov, Nicholas Mecham and Taylor Grubbs

Fluids 2025, 10(4), 85; https://doi.org/10.3390/fluids10040085 - 26 Mar 2025

Viewed by 210

Abstract

The research objective of this work was to improve the engineering predictions of the turbulence characteristics of flows in curved narrow channels. Such channel flows are commonly encountered in nuclear research and test reactors, with one of them being the high-flux isotope reactor [...] Read more.

The research objective of this work was to improve the engineering predictions of the turbulence characteristics of flows in curved narrow channels. Such channel flows are commonly encountered in nuclear research and test reactors, with one of them being the high-flux isotope reactor (HFIR). Research reactors bear high heat fluxes, and the proper computing of turbulence is paramount for safe and reliable reactor operation. The study builds on the results of a previous direct numerical simulation of turbulence to inform a well-known Reynolds-averaged Navier–Stokes shear-stress turbulence model and improves its accuracy in simulating parallel channel flows. A new formulation of the loss term in the dissipation conservation equation is suggested. Combined with high wall distance computational grids, the new implementation provides a fast-running flow solution, suitable for engineering purposes. Model generalization for parallel channel flows, in a broader range of frictional Reynolds numbers, is suggested by introducing a new form of the model constants. Full article

(This article belongs to the Special Issue Modelling Flows in Pipes and Channels)

► Show Figures

Figure 1

22 pages, 2043 KiB

Open AccessArticle

Spectral Analysis of Confined Cylinder Wakes

by Wilson Lu, Leon Chan and Andrew Ooi

Fluids 2025, 10(4), 84; https://doi.org/10.3390/fluids10040084 - 25 Mar 2025

Viewed by 200

Abstract

Bluff body flows, while commonly assumed to be isolated, are often subject to confinement effects due to interactions with nearby objects. In this study, a simple approximation of such a flow configuration is considered, where a cylinder is placed symmetrically within an infinite [...] Read more.

Bluff body flows, while commonly assumed to be isolated, are often subject to confinement effects due to interactions with nearby objects. In this study, a simple approximation of such a flow configuration is considered, where a cylinder is placed symmetrically within an infinite channel. The presence of walls implies the wake is physically confined and introduces interactions between the wake and the boundary layer along the wall. To isolate the effect of confinement, simulations are conducted with slip channel walls, removing the boundary layers. Comparisons of flow statistics between simulations of slip and no-slip channel walls show minor differences at a low blockage ratio,

β

(defined as the ratio of cylinder diameter to channel height), while for larger blockage ratios, the differences are significant. Spectral analysis is also performed on the wake and shear layers. At the lowest blockage,

β = 0.3

, little modification is made to the wake, and we find that Kármán vortices are one-way coupled to the boundary layers along the walls. For

β = 0.5

, wall–wake interactions are determined to significantly contribute to wake dynamics, thus to two-way coupling Kármán vortices and the wall boundary layers. Finally, for

β = 0.7

, the absence of Kármán shedding couples Kelvin–Helmoltz vortices in the shear layer, separating off the cylinder to the wall boundary layer. Full article

(This article belongs to the Special Issue Aerodynamics and Aeroacoustics of Vehicles, 4th Edition)

► Show Figures

Figure 1

16 pages, 7554 KiB

Open AccessReview

Tabulated Chemistry Models for Numerical Simulation of Combustion Flow Field

by Masaya Muto

Fluids 2025, 10(4), 83; https://doi.org/10.3390/fluids10040083 - 25 Mar 2025

Viewed by 256

Abstract

In numerical simulations of combustion flow fields, tabulated chemistry models are widely used to reduce computational cost compared to rigorous reaction calculation methods such as detailed chemical reaction calculations. Tabulated combustion data are generated by performing low-dimensional combustion calculations prior to simulating the [...] Read more.

In numerical simulations of combustion flow fields, tabulated chemistry models are widely used to reduce computational cost compared to rigorous reaction calculation methods such as detailed chemical reaction calculations. Tabulated combustion data are generated by performing low-dimensional combustion calculations prior to simulating the combustion flow field. The results are then stored in a database indexed by parameters such as mixture fraction and reaction progress variables. In recent years, significant advancements have been made in the tabulation of combustion data to accommodate diverse fuels and replicate the complex conditions observed in practical combustion systems. This review paper provides an overview of recent developments in tabulated chemistry models, particularly those based on the flamelet/progress-variable method. It specifically addresses scenarios involving multi-point fuel injection, the presence of heat loss factors in combustion flow fields, the consideration of varying diffusion coefficients, and other complex phenomena. Full article

(This article belongs to the Special Issue Turbulence and Combustion)

► Show Figures

Figure 1

24 pages, 3605 KiB

Open AccessReview

Solution Combustion Synthesis for Various Applications: A Review of the Mixed-Fuel Approach

by Samantha Padayatchee, Halliru Ibrahim, Holger B. Friedrich, Ezra J. Olivier and Pinkie Ntola

Fluids 2025, 10(4), 82; https://doi.org/10.3390/fluids10040082 - 25 Mar 2025

Viewed by 503

Abstract

As solution combustion synthesis (SCS) becomes a universal route to metal oxide nanomaterials, it also paves the way for mixed-fuel combustion synthesis as an advanced approach to the synthesis of materials of desirable properties for diverse applications. Major significance is attached to the [...] Read more.

As solution combustion synthesis (SCS) becomes a universal route to metal oxide nanomaterials, it also paves the way for mixed-fuel combustion synthesis as an advanced approach to the synthesis of materials of desirable properties for diverse applications. Major significance is attached to the rates of decomposition and combustion temperatures of the fuel as determinant factors of the morphology and physicochemical properties of the materials obtained. This has promoted the use of mixed-fuel systems characterized by lower decomposition temperatures of organic fuels and higher rates of combustion. The review work presented herein provides a comprehensive analysis of the applications of mixed-fuel SCS in ceramics, fuel cells, nanocomposite materials, and the recycling of lithium battery materials while taking into consideration the effects of the mixed-fuel system on the physicochemical and morphological properties of those materials, as compared to their analogues prepared via single-fuel SCS. Full article

(This article belongs to the Special Issue Turbulence and Combustion)

► Show Figures

Figure 1

21 pages, 8213 KiB

Open AccessArticle

Numerical Investigation of Cylindrical Water Droplets Subjected to Air Shock Loading at a High Weber Number

by F. Edoardo Taglialatela and Giuliano De Stefano

Fluids 2025, 10(4), 81; https://doi.org/10.3390/fluids10040081 - 25 Mar 2025

Viewed by 309

Abstract

This work is devoted to the computational investigation of the deformation and breakup of cylindrical water bodies in the high-speed airflow behind incident shock waves. Both single-column and tandem-column configurations in various arrangements were simulated by reproducing the shock/droplet interaction process in a [...] Read more.

This work is devoted to the computational investigation of the deformation and breakup of cylindrical water bodies in the high-speed airflow behind incident shock waves. Both single-column and tandem-column configurations in various arrangements were simulated by reproducing the shock/droplet interaction process in a shock-tube device. The calculations were conducted by using a third-party solver recently developed for compressible two-phase flows in the framework of the open source finite volume toolbox OpenFOAM. The numerical approach is based on the use of the volume-of-fluid method to resolve the phase interface, where a particular discretization technique allows us to prevent unphysical instabilities. The numerical scheme makes use of more precise information of the local propagation speeds to maintain a high resolution and a small numerical viscosity. Qualitative and quantitative comparisons of the results with reference experimental and numerical data demonstrated good agreement for the main characteristics of the interaction process in terms of the morphology, dynamics, and breakup of the deforming water bodies. Full article

(This article belongs to the Special Issue 10th Anniversary of Fluids—Recent Advances in Fluid Mechanics)

► Show Figures

Figure 1

27 pages, 23553 KiB

Open AccessArticle

Numerical Study of a Hydraulic Turbine Designed from Centrifugal Atomizers Theory Varying Its Inlet Parameters

by Daniel Calzada, Anderson Uribe, Julio Ronceros, Dante Vargas, Carlos Raymundo, Wilder Namay, Gianpierre Zapata and Gustavo Ronceros

Fluids 2025, 10(4), 80; https://doi.org/10.3390/fluids10040080 - 25 Mar 2025

Viewed by 279

Abstract

This study analyzes the feasibility of using pressure swirl atomizers at scale as energy generators. Likewise, the Ansys Fluent numerical simulation tool was used, configured based on the Volume of Fluid (VOF) multiphase model and six DOF motion for rigid bodies. In turn, [...] Read more.

This study analyzes the feasibility of using pressure swirl atomizers at scale as energy generators. Likewise, the Ansys Fluent numerical simulation tool was used, configured based on the Volume of Fluid (VOF) multiphase model and six DOF motion for rigid bodies. In turn, three configurations of feeding flow were tested: upper manifold, lower manifold, and dual manifold. The numerical results show that it is possible to produce mechanical energy with 29.4% and 32.9% efficiency (using the SST k-

ω

and k-

ε

turbulence model, respectively), while generating a uniform spray effect at the outlet of the atomizer, even though this has certain ovoid-type deformities. Likewise, it was found that the addition of an internal rotor to the swirl chamber caused the generation of a very low-pressure contour, leading to an increase in the mass flow consumption of the atomizer. Also, four cases were analyzed, considering a hydraulic supply of both manifolds: 250 kPa, 300 kPa, 350 kPa, and 400 kPa, in order to obtain the characteristic curve of the turbine depending on the mass flow obtained for each case. Finally, this research proves how viable the use of this type of technology is in the field of renewable energy generation and the impact on its performance under different configurations of hydraulic supply. Full article

► Show Figures

Figure 1

14 pages, 263 KiB

Open AccessArticle

Renormalization Group Approach as a Symmetry Transformation for an Analysis of Non-Newtonian Elastic Turbulence

by Andriy A. Avramenko, Igor V. Shevchuk, Nataliia P. Dmitrenko and Alina V. Konyk

Fluids 2025, 10(4), 79; https://doi.org/10.3390/fluids10040079 - 24 Mar 2025

Viewed by 140

Abstract

Symmetry transformation methods are widely used in fluid flow problems. One such method is renormalization group analysis. Renormalization group methods are used to develop a macroscopic turbulence model for non-Newtonian fluids (Oldroyd-B type). This model accounts for the large-distance and large-time behavior of [...] Read more.

Symmetry transformation methods are widely used in fluid flow problems. One such method is renormalization group analysis. Renormalization group methods are used to develop a macroscopic turbulence model for non-Newtonian fluids (Oldroyd-B type). This model accounts for the large-distance and large-time behavior of velocity correlations generated by the momentum equation for a randomly stirred, incompressible flow and does not account for empirical constants. The aim of this mathematical study was to develop a k-ε RNG turbulence model for non-Newtonian fluids (Oldroyd-B type). For the first time, using the renormalization procedure, the transport equations for the large-scale modes and expressions for effective transport coefficients are obtained. Expressions for the renormalized turbulent viscosity are also derived. This model explains the phenomenon of the abrupt growth of the irregularity of velocity at low values of the Reynolds number. Full article

(This article belongs to the Special Issue Advances in Computational Mechanics of Non-Newtonian Fluids)

28 pages, 615 KiB

Open AccessReview

A Review of Oscillators in Hydrokinetic Energy Harnessing Through Vortex-Induced Vibrations

by Deping Cao, Jie He, Hanqi Zeng, Yijia Zhu, Sean Zixuan Chan, Mark Ravinpal Williams, Ivan Zhi Liang Khor, Omkar Venkata Yalla, Mohammed R. Sunny, Ritwik Ghoshal, Anirban Bhattacharyya, Swapnadip De Chowdhury, Zaibin Lin, Cheng Siong Chin and Hao Chen

Fluids 2025, 10(4), 78; https://doi.org/10.3390/fluids10040078 - 24 Mar 2025

Viewed by 406

Abstract

This review investigates the role of vortex-induced vibrations (VIVs) in hydrokinetic energy harnessing, shedding light on their dual nature as both a challenge in offshore engineering and an untapped resource for renewable energy. VIVs serve as a novel energy source, converting the kinetic [...] Read more.

This review investigates the role of vortex-induced vibrations (VIVs) in hydrokinetic energy harnessing, shedding light on their dual nature as both a challenge in offshore engineering and an untapped resource for renewable energy. VIVs serve as a novel energy source, converting the kinetic energy of fluid flows into mechanical or electrical power. The review discusses the various energy conversion mechanisms, highlighting the unique benefits and challenges of electromagnetic, piezoelectric, and triboelectric systems. A significant emphasis is placed on optimizing VIV energy harnessing to balance maximizing energy output while maintaining structural stability. The review provides insights into the geometric configurations, material properties, and advanced computational methods that are pivotal in this optimisation process. In conclusion, this review provides a comprehensive analysis of the current progress and persistent challenges in VIV research, offering actionable insights and innovative solutions that will advance the field of efficient and sustainable energy. Full article

(This article belongs to the Special Issue Marine Hydrodynamics: Theory and Application)

► Show Figures

Figure 1

23 pages, 11481 KiB

Open AccessArticle

Dimensionless Analysis of Rough Roadway Airflow Distribution Based on Numerical Simulations

by Zongcheng Jia, Qiang Zhao, Yan Zhao, Baoyu Cui and Tao Song

Fluids 2025, 10(4), 77; https://doi.org/10.3390/fluids10040077 - 23 Mar 2025

Viewed by 258

Abstract

As resources are extracted from the deeper sections of a mine, the ventilation network becomes increasingly complex. Consequently, determining the optimal installation location for speed-measuring equipment that accurately reflects the average wind speed along the roadway remains a challenging task. In this study, [...] Read more.

As resources are extracted from the deeper sections of a mine, the ventilation network becomes increasingly complex. Consequently, determining the optimal installation location for speed-measuring equipment that accurately reflects the average wind speed along the roadway remains a challenging task. In this study, two three-dimensional geometric models, smooth and rough, were developed based on field conditions. The cross-sectional widths, heights, and flow velocities of the model channels were processed dimensionlessly. The dimensionless velocity distributions of the smooth and rough models were then analyzed for different Reynolds numbers. It was observed that the dimensionless average velocity ring distributions for the rough model were smaller than those for the smooth model. Additionally, the maximum values of dimensionless flow velocities were negatively correlated with the flow velocities under laminar flow conditions, whereas they largely overlapped under turbulent flow. The dimensionless distances of the average velocity rings from the top and sidewalls of the channel were studied and determined for both models across different flow regimes. Specifically, the dimensionless distance values

d (-)

were found to be 0.111 for the smooth model and 0.101 for the rough model under the laminar regime. Under the turbulence regime, the corresponding values were 0.106 and 0.108. Likewise, the values of

h (-)

were 0.135 and 0.135 for the smooth and rough models in the laminar flow regime, while under turbulent flow, the values were 0.131 and 0.162, respectively. The largest dimensionless velocity value was identified at the center of the velocity distribution circle. For corners that did not maintain simple parallelism with the walls, these regions were incorporated into the circle equation using the Least Squares Method, providing a theoretical basis for the placement of velocity-measuring equipment in practical applications. By using the sidewall as the reference coordinate, an appropriate mathematical model was employed to establish the functional relationship between the centerline velocity of the roadway and the dimensionless horizontal coordinate. The fitting results showed good agreement, and this model can be used to back-calculate and expand the potential installation locations for a mine anemometer. Full article

► Show Figures

Figure 1

Journal Menu

Journal Browser

Fluids, Volume 10, Issue 4 (April 2025) – 32 articles

Further Information

Guidelines

MDPI Initiatives

Follow MDPI