Fluids

24 pages, 5597 KiB

Open AccessArticle

Analysis of Two Protection Strategies for Reducing Aerosol Expulsion from Wind Instruments

by Miriam Baron, Bogac Tur, Marie Köberlein, Laila Ava Hermann, Sophia Gantner, Matthias Echternach and Stefan Kniesburges

Fluids 2025, 10(5), 116; https://doi.org/10.3390/fluids10050116 - 30 Apr 2025

Abstract

(1) Background: the aim of this study is to assess the effectiveness of two protection systems for aerosol cloud reduction while playing different wind instruments. (2) Methods: The protection systems used were a cotton molton construction combined with a bell filter attached at [...] Read more.

(1) Background: the aim of this study is to assess the effectiveness of two protection systems for aerosol cloud reduction while playing different wind instruments. (2) Methods: The protection systems used were a cotton molton construction combined with a bell filter attached at the bell of the instruments, as well as a household paper towel. For visualization of the emitted aerosol particles, e-cigarettes were used. With three full HD cameras, cloud dispersion was captured in the forward, sideways, and upwards directions. The effectiveness of aerosol spread reduction was statistically evaluated. (3) Results: Without protection, aerosol clouds dispersed, on average, up to 1.23 m in the forward direction, 0.46 m sideways, and 0.86 m upwards. The cotton molton mask reduced forward spread by 42%, while the paper towel achieved a 15% reduction, although both systems increased lateral and vertical dispersion. Specifically, the cotton molton mask yielded a 9% increase to the side and 7% in the upward direction, while the paper towel resulted in a 66% increase to the sides and a 10% increase in the upward direction. The cotton molton mask’s effectiveness was attributed to its additional coverage of the tone holes, which contribute to aerosol emission in woodwind instruments. A statistical analysis via the Friedman test confirmed significant reductions in forward dispersion with the cotton molton system. (4) Conclusions: Protective systems can partially reduce aerosol emissions. However, these alone are not sufficient, and further measures to reduce the spread of particles are necessary. Full article

22 pages, 4445 KiB

Open AccessArticle

Research on Dual-Mode Self-Calibration Tensioning System

by Xuling Liu, Yusong Zhang, Chaofeng Peng, Le Bo, Kaiyi Zhang, Guoyong Ye, Jinggan Shao, Jinghui Peng and Songjing Li

Fluids 2025, 10(5), 115; https://doi.org/10.3390/fluids10050115 - 30 Apr 2025

Abstract

In this paper, a double-mode self-calibration tension system is proposed, which adopts the conversion of hydraulic meter tension and the monitoring of standard force sensors. According to the material characteristics of the jack and the viscosity and temperature characteristics of the hydraulic oil, [...] Read more.

In this paper, a double-mode self-calibration tension system is proposed, which adopts the conversion of hydraulic meter tension and the monitoring of standard force sensors. According to the material characteristics of the jack and the viscosity and temperature characteristics of the hydraulic oil, the differential model of heat conduction in the hydraulic cylinder and the mathematical model of oil film friction heat generation are established, and the internal thermodynamic characteristics of the jack are theoretically analyzed, which provides theoretical support for the temperature compensation of the hydraulic oil pressure gauge of the jack. A simulation analysis was conducted on the thermodynamic characteristics of the hydraulic jack, and the distribution patterns of the temperature field, thermal stress field, and thermal strain field inside the hydraulic cylinder during normal operation were determined by measuring the temperature changes in five different parts of the jack at different times (t = 200 s, 2600 s, 5000 s, 7400 s, and 10,000 s). For the issue of heat generation due to oil film friction in the hydraulic jack, a simulation calculation model is developed by integrating Computational Fluid Dynamics (CFD) techniques with dynamic grid and slip grid methods. By simulating and analyzing frictional heating under conditions where the inlet pressures are 0.1 MPa, 0.3 MPa, 0.5 MPa, 0.7 MPa, and 0.9 MPa, respectively, we can obtain the temperature distribution on the jack, determine the frictional resistance, and subsequently conduct a theoretical analysis of the simulation results. Using the high-precision standard force sensor after data processing and the hydraulic oil gauge after temperature compensation, the online self-calibration of the tensioning system is carried out, and the regression equation of the tensioning system under different oil temperatures is obtained. The double-mode self-calibration tensioning system with temperature compensation is used to verify the compensation accuracy of the proposed double-mode self-calibration tensioning system. Full article

(This article belongs to the Topic Applied Heat Transfer)

► Show Figures

Figure 1

22 pages, 3296 KiB

Open AccessArticle

Performance of an L-Shaped Duct OWC-WEC Integrated into Vertical and Sloped Breakwaters by Using a Free-Surface RANS-Based Numerical Model

by Eric Didier and Paulo R. F. Teixeira

Fluids 2025, 10(5), 114; https://doi.org/10.3390/fluids10050114 - 30 Apr 2025

Abstract

Waves generated by the wind in oceans and seas have a significant available quantity of clean and renewable energy. However, harvesting their energy is still a challenge. The integration of an oscillating water column (OWC) wave energy converter into a breakwater leads to [...] Read more.

Waves generated by the wind in oceans and seas have a significant available quantity of clean and renewable energy. However, harvesting their energy is still a challenge. The integration of an oscillating water column (OWC) wave energy converter into a breakwater leads to more viability, since it allows working as both harbor and coastal protection and harvesting wave energy. The main objective of this study is to investigate different configurations of L-shaped duct OWC devices inserted into vertical and sloped (2:3) impermeable breakwaters for different lengths of the lip by using a numerical model based on the Reynolds-Averaged Navier-Stokes equations. The ANSYS FLUENT^® software (2016) is used in 2D numerical simulations by adopting the volume of fluid method to consider the two-phase free surface flow (water and air). It was observed that both the length of the lip and the length of the L-shaped duct OWC significantly influence the resonance and the efficiency of the OWC device. In addition, the performance of the OWC device varies significantly with its geometric configuration, which needs to be adapted for the local sea state. Full article

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

► Show Figures

Figure 1

26 pages, 9399 KiB

Open AccessArticle

Investigation of Multiphase Flow in Continuous-Casting Water Model with Measurements and Computational Modeling

by Hamed Olia, Dylan Palmer, Ehsan Jebellat and Brian G. Thomas

Fluids 2025, 10(5), 113; https://doi.org/10.3390/fluids10050113 - 28 Apr 2025

Abstract

This work introduces a 0.6-scale water model of the continuous slab-casting process and a MATLAB-based model to study the effects of non-primed and multiphase flow on pressure and flow rate. The water model uses stopper-rod flow control and features pressure and velocity measurements [...] Read more.

This work introduces a 0.6-scale water model of the continuous slab-casting process and a MATLAB-based model to study the effects of non-primed and multiphase flow on pressure and flow rate. The water model uses stopper-rod flow control and features pressure and velocity measurements at multiple locations. The new computational model, PFSR V4 (Pressure-drop Flow-rate model of Stopper Rod metal delivery systems, Version 4), improves upon a prior one-dimensional Bernoulli-based framework by incorporating a bubble accumulation zone. This zone represents a region of bubbly flow with an intermediate gas fraction between constant-pressure gas pockets below the stopper tip and the downstream bubbly flow regime. Parametric studies with the water model show that flow remains fully primed at low gas flow rates but transitions to non-primed flow as the gas flow rate exceeds 10–16 SLPM. Three different flow regions are observed inside the water model nozzle: air pocket, bubble accumulation, and bubbly flow, which are also captured by the new computational model. Above a critical gas flow rate, the flow becomes unstable and difficult to control, though higher hot gas flow rates are expected for similar transitions in a real steel caster due to gas expansion at high temperatures. Pressure changes are minimal in the air pocket region and increase significantly in the upper bubble accumulation zone, where liquid velocity is much higher than in the classic bubbly-flow region, found lower in the nozzle. The new model was successfully calibrated to match the observed flow regimes and shows good agreement with the water-model measurements. Full article

(This article belongs to the Special Issue Multiphase Flow for Industry Applications)

► Show Figures

Figure 1

19 pages, 5624 KiB

Open AccessArticle

Research on the Improvement of BEM Method for Ultra-Large Wind Turbine Blades Based on CFD and Artificial Intelligence Technologies

by Shiyu Yang, Mingming Zhang, Yu Feng, Haikun Jia, Na Zhao and Qingwei Chen

Fluids 2025, 10(5), 112; https://doi.org/10.3390/fluids10050112 - 27 Apr 2025

Abstract

With the development of the wind power industry, wind turbine blades are increasingly adopting ultra-large-scale designs. However, as the size of blades continues to increase, existing aerodynamic calculation methods struggle to achieve both relatively high computational accuracy and efficiency simultaneously. To tackle this [...] Read more.

With the development of the wind power industry, wind turbine blades are increasingly adopting ultra-large-scale designs. However, as the size of blades continues to increase, existing aerodynamic calculation methods struggle to achieve both relatively high computational accuracy and efficiency simultaneously. To tackle this challenge, this research focuses on the low accuracy issues of the traditional Blade Element Momentum theory (BEM) in predicting the aerodynamic performance of wind turbine blades. Consequently, a correction framework is proposed, to integrate the Computational Fluid Dynamics (CFD) method with the Multilayer Perceptron (MLP) neural network. In this approach, the CFD method is used to predict the airflow characteristics around the blades, and the MLP neural network is employed to model the intricate functional relationships between multiple influencing factors and key aerodynamic parameters. This process results in high-precision predictive functions for key aerodynamic parameters, which are then used to correct the traditional BEM. When this correction framework is applied to the rotor of the IEA 15 MW wind turbine, the effectiveness of MLP in predicting key aerodynamic parameters is demonstrated. The research findings suggest that this framework can enhance the accuracy of BEM aerodynamic load predictions to a level comparable to that of RANS. Full article

(This article belongs to the Special Issue Drag Reduction Through Traditional or Machine Learning-Based Flow Control)

► Show Figures

Figure 1

15 pages, 326 KiB

Open AccessArticle

Weakly Nonlinear Instability of a Convective Flow in a Plane Vertical Channel

by Natalja Budkina, Valentina Koliskina, Andrei Kolyshkin and Inta Volodko

Fluids 2025, 10(5), 111; https://doi.org/10.3390/fluids10050111 - 26 Apr 2025

Abstract

The weakly nonlinear stability analysis of a convective flow in a planar vertical fluid layer is performed in this paper. The base flow in the vertical direction is generated by internal heat sources distributed within the fluid. The system of Navier–Stokes equations under [...] Read more.

The weakly nonlinear stability analysis of a convective flow in a planar vertical fluid layer is performed in this paper. The base flow in the vertical direction is generated by internal heat sources distributed within the fluid. The system of Navier–Stokes equations under the Boussinesq approximation and small-Prandtl-number approximation is transformed to one equation containing a stream function. Linear stability calculations with and without a small-Prandtl-number approximation lead to the range of the Prantdl numbers for which the approximation is valid. The method of multiple scales in the neighborhood of the critical point is used to construct amplitude evolution equation for the most unstable mode. It is shown that the amplitude equation is the complex Ginzburg–Landau equation. The coefficients of the equation are expressed in terms of integrals containing the linear stability characteristics and the solutions of three boundary value problems for ordinary differential equations. The results of numerical calculations are presented. The type of bifurcation (supercritical bifurcation) predicted by weakly nonlinear calculations is in agreement with experimental data. Full article

► Show Figures

Figure 1

20 pages, 3854 KiB

Open AccessArticle

EHD Instability Modes of Power-Law Fluid Jet Issuing in Gaseous Streaming via Permeable Media

by Mohamed F. El-Sayed, Mohamed F. E. Amer and Doaa M. Mostafa

Fluids 2025, 10(5), 110; https://doi.org/10.3390/fluids10050110 - 25 Apr 2025

Abstract

The instability of a non-Newtonian dielectric fluid jet of power-law (P-L) type injected when streaming dielectric gas through porous media is examined using electrohydrodynamic (EHD) linear analysis. The interfacial boundary conditions (BCs) are used to derive the dispersion relation for both shear-thinning (s-thin) [...] Read more.

The instability of a non-Newtonian dielectric fluid jet of power-law (P-L) type injected when streaming dielectric gas through porous media is examined using electrohydrodynamic (EHD) linear analysis. The interfacial boundary conditions (BCs) are used to derive the dispersion relation for both shear-thinning (s-thin) and shear-thickening (s-thick) fluids. A detailed discussion is outlined on the impact of dimensionless flow parameters. The findings show that jet breakup can be categorized into two instability modes: Rayleigh (RM) and Taylor (TM), respectively. For both fluids, the system in TM is found to be more unstable than that found in RM, and, for s-thick fluids, it is more unstable. For all P-L index values, the system is more unstable if a porous material exists than when it does not. It is demonstrated that the generalized Reynolds number (

{R e}_{n}

), Reynolds number (

R e

), P-L index, dielectric constants, gas-to-liquid density, and viscosity ratios have destabilizing influences; moreover, the Weber number (

W e

), electric field (EF), porosity, and permeability of the porous medium have a stabilizing impact. Depending on whether its value is less or more than one, the velocity ratio plays two different roles in stability, and the breakup length and size of P-L fluids are connected to the maximal growth level and the instability range in both modes. Full article

► Show Figures

Figure 1

37 pages, 15268 KiB

Open AccessReview

Subchannel Reactor Studies: Applications and Advances Using Lattice Boltzmann Method—Comprehensive Review Study

by Abutiatey Eugene and Pil-Seung Chung

Fluids 2025, 10(5), 109; https://doi.org/10.3390/fluids10050109 - 25 Apr 2025

Abstract

Computational fluid dynamics (CFD) is an instrumental tool used in tackling the challenges of flow behavior and safety within nuclear reactor cores. Traditional CFD methods like finite volume, finite element, and finite difference have driven significant progress in nuclear engineering, particularly in single-phase [...] Read more.

Computational fluid dynamics (CFD) is an instrumental tool used in tackling the challenges of flow behavior and safety within nuclear reactor cores. Traditional CFD methods like finite volume, finite element, and finite difference have driven significant progress in nuclear engineering, particularly in single-phase and two-phase flow modeling, multiscale analysis, and multiphysics coupling. However, the Lattice Boltzmann Method (LBM), an advancing CFD tool for nuclear reactor subchannel study, remains underexplored in this field. LBM takes a unique mesoscopic approach by modeling particle distributions on a discrete lattice, offering a bridge between microscopic dynamics and macroscopic continuum behavior. Since the integration of LBM into the Lattice Bhatnagar–Gross–Krook (LBGK) model, it has significantly advanced, proving its efficiency in handling complex flow conditions. This review explores the potential of LBM in nuclear reactor subchannel applications. This study emphasizes LBM as a robust computational tool for subchannel study by highlighting its strengths, limitations, and future possibilities. Full article

► Show Figures

Figure 1

13 pages, 987 KiB

Open AccessArticle

Concentration Monitoring of Highly-Diluted Crude Oil-In-Water Emulsions by Ultrasonic Backscattering Sensors

by Carlos A. B. Reyna, Ediguer E. Franco, Santiago Laín, Timoteo F. de Oliveira, Marcos S. G. Tsuzuki and Flávio Buiochi

Fluids 2025, 10(5), 108; https://doi.org/10.3390/fluids10050108 - 25 Apr 2025

Abstract

This work deals with the feasibility of ultrasonic monitoring of the crude oil content in highly diluted crude oil-in-water emulsions, common mixtures obtained in the coalescence process of the petroleum industry. The measurement principle is the determination of the time of flight using [...] Read more.

This work deals with the feasibility of ultrasonic monitoring of the crude oil content in highly diluted crude oil-in-water emulsions, common mixtures obtained in the coalescence process of the petroleum industry. The measurement principle is the determination of the time of flight using the reflected pulses from a set of scatterers located in the near field of commercial transducers of 5 and 10 MHz. Dispersers consist of two rows of metal wires tensioned in front of the transducer using a specially designed mechanical part. The resulting assembly is a probe that can be introduced into a tank or pipe to perform the measurement. Experiments with crude oil-in-water emulsions with concentrations from 10 to 2000 ppm (parts per million) at a temperature of 20 °C were carried out. The results show that the small changes in the propagation velocity resulting from changes in concentration and temperature can be detected by the developed ultrasonic sensor. This opens up the possibility of determining the oil content in the emulsion by means of a calibration approach. The main motivation is the development of techniques for real-time monitoring of crude oil content in the wastewater produced in the petroleum industry. Full article

(This article belongs to the Special Issue Numerical Modeling and Experimental Studies of Two-Phase Flows, 2nd Edition)

► Show Figures

Figure 1

18 pages, 6280 KiB

Open AccessArticle

Hydrodynamic Resistance Analysis of Large Biomimetic Yellow Croaker Model: Effects of Shape, Body Length, and Material Based on CFD

by Donglei Zhao, Kexiang Lu and Weiguo Qian

Fluids 2025, 10(5), 107; https://doi.org/10.3390/fluids10050107 - 24 Apr 2025

Abstract

The marine environment is highly complex, characterized by substantial fluctuations in flow velocity. To enhance the adaptability of robotic large yellow croakers to such conditions, this study takes into account multiple factors, including shape, dimensions, and material properties, and evaluates their hydrodynamic resistance [...] Read more.

The marine environment is highly complex, characterized by substantial fluctuations in flow velocity. To enhance the adaptability of robotic large yellow croakers to such conditions, this study takes into account multiple factors, including shape, dimensions, and material properties, and evaluates their hydrodynamic resistance characteristics. A 2D model of large yellow croakers aged 1, 4, 7, 10, and 12 months was established as the bionic object. Based on computational fluid dynamics, the water resistance characteristics of this model were investigated in the same water environment. A 3D model of this species based on the 2D model and three skin materials, PE, PC, and ST, was added, and the effects of these materials on the water resistance of the 3D model were investigated. It was shown that in a water environment with a current speed of 0.1~1 m/s, the water resistance of large yellow croaker models at different ages ranged from 0.1006 to 6.8485 N; that of croakers with different body lengths ranged from 0.1067 to 28.5760 N; and that of croakers with different skin materials ranged from 0.0048 to 0.8672 N. The results showed that in the water environment with a current speed of 0.1–1 m/s, the 12-month-old large yellow croaker model had a lower water resistance range of 0.1006~3.6512 N in the watershed compared with other models of the same age; the large yellow croaker models with body lengths of 20, 30, and 40 cm had a smaller range of water resistance of 0.1125~12.5110 N in the watershed compared with other models of the same body length; and large yellow croaker models made of PE had a smaller range of resistance of 0.0048~0.7523 N in the watershed compared to those made of PC and ST materials. The results of this study are important for the design and fabrication of robotic fish capable of prolonged underwater operations. Full article

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

► Show Figures

Figure 1

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

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

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

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

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

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

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

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

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

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

Journal Description

Fluids

Latest Articles

Journal Menu

Journal Browser

Highly Accessed Articles

Latest Books

E-Mail Alert

News

Topics

Conferences

Special Issues

Topical Collections

Further Information

Guidelines

MDPI Initiatives

Follow MDPI