Fluids

19 pages, 4054 KiB

Open AccessArticle

Evaluation of Flow-Induced Shear in a Porous Microfluidic Slide: CFD Analysis and Experimental Investigation

by Manoela Neves, Gayathri Aparnasai Reddy, Anitha Niyingenera, Norah Delaney, Wilson S. Meng and Rana Zakerzadeh

Fluids 2025, 10(6), 160; https://doi.org/10.3390/fluids10060160 - 17 Jun 2025

Viewed by 960

Abstract

Microfluidic devices offer well-defined physical environments that are suitable for effective cell seeding and in vitro three-dimensional (3D) cell culture experiments. These platforms have been employed to model in vivo conditions for studying mechanical forces, cell–extracellular matrix (ECM) interactions, and to elucidate transport [...] Read more.

Microfluidic devices offer well-defined physical environments that are suitable for effective cell seeding and in vitro three-dimensional (3D) cell culture experiments. These platforms have been employed to model in vivo conditions for studying mechanical forces, cell–extracellular matrix (ECM) interactions, and to elucidate transport mechanisms in 3D tissue-like structures, such as tumor and lymph node organoids. Studies have shown that fluid flow behavior in microfluidic slides (µ-slides) directly influences shear stress, which has emerged as a key factor affecting cell proliferation and differentiation. This study investigates fluid flow in the porous channel of a µ-slide using computational fluid dynamics (CFD) techniques to analyze the impact of perfusion flow rate and porous properties on resulting shear stresses. The model of the µ-slide filled with a permeable biomaterial is considered. Porous media fluid flow in the channel is characterized by adding a momentum loss term to the standard Navier–Stokes equations, with a physiological range of permeability values. Numerical simulations are conducted to obtain data and contour plots of the filtration velocity and flow-induced shear stress distributions within the device channel. The filtration flow is subsequently measured by performing protein perfusions into the slide embedded with native human-derived ECM, while the flow rate is controlled using a syringe pump. The relationships between inlet flow rate and shear stress, as well as filtration flow and ECM permeability, are analyzed. The findings provide insights into the impact of shear stress, informing the optimization of perfusion conditions for studying tissues and cells under fluid flow. Full article

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

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27 pages, 16552 KiB

Open AccessArticle

Vertical Dense Jets in Crossflows: A Preliminary Study with Lattice Boltzmann Methods

by Maria Grazia Giordano, Jérôme Jacob, Piergiorgio Fusco, Sabina Tangaro and Daniela Malcangio

Fluids 2025, 10(6), 159; https://doi.org/10.3390/fluids10060159 - 16 Jun 2025

Viewed by 334

Abstract

The dramatic increase in domestic and industrial waste over recent centuries has significantly polluted water bodies, threatening aquatic life and human activities such as drinking, recreation, and commerce. Understanding pollutant dispersion is essential for designing effective waste management systems, employing both experimental and [...] Read more.

The dramatic increase in domestic and industrial waste over recent centuries has significantly polluted water bodies, threatening aquatic life and human activities such as drinking, recreation, and commerce. Understanding pollutant dispersion is essential for designing effective waste management systems, employing both experimental and computational techniques. Among Computational Fluid Dynamics (CFD) techniques, the Lattice Boltzmann Method (LBM) has emerged as a novel approach based on a discretized Boltzmann equation. The versatility and parallelization capability of this method makes it particularly attractive for fluid dynamics simulations using high-performance computing. Motivated by its successful application across various scientific disciplines, this study explores the potential of LBM to model pollutant mixing and dilution from outfalls into surface water bodies, focusing specifically on vertical dense jets in crossflow (JICF), a key scenario for the diffusion of brine from desalination plants. A full-LBM scheme is employed to model both the hydrodynamics and the transport of the saline concentration field, and Large Eddy Simulations (LES) are employed in the framework of LBM to reduce computational costs typically associated with turbulence modeling, together with a recursive regularization procedure for the collision operator to achieve greater stability. Several key aspects of vertical dense JICF are considered. The simulations successfully capture general flow characteristics corresponding to jets with varying crossflow parameter

u_{r} F

and most of the typical vortical structures associated with JICF. Relevant quantities such as the terminal rise height, the impact distance, the dilution at the terminal rise height, and the dilution at the impact point are compared with experimental results and semi-empirical relations. The results show a systematic underestimation of these quantities, but the key trends are successfully captured, highlighting LBM’s promise as a tool for simulating wastewater dispersion in aquatic environments. Full article

(This article belongs to the Special Issue CFD Applications in Environmental Engineering)

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14 pages, 2047 KiB

Open AccessArticle

Computational Fluid Dynamics Modeling of Sweep Gas Flow Rate-Dependent Carbon Dioxide Removal in Oxygenators

by Keira Askew, Julia Rizzo, Lei Fan and Ge He

Fluids 2025, 10(6), 158; https://doi.org/10.3390/fluids10060158 - 15 Jun 2025

Viewed by 354

Abstract

Computational fluid dynamics (CFD) models have been widely used to evaluate the hydrodynamic and gas exchange performances of oxygenators, which are crucial in supporting patients with lung diseases or failure. However, while CFD models have been effective in analyzing oxygen transfer, they have [...] Read more.

Computational fluid dynamics (CFD) models have been widely used to evaluate the hydrodynamic and gas exchange performances of oxygenators, which are crucial in supporting patients with lung diseases or failure. However, while CFD models have been effective in analyzing oxygen transfer, they have not adequately addressed the experimentally demonstrated effects of varying sweep gas flow rates on CO₂ removal. This is a critical gap, as sweep gas flow directly influences the CO₂ transfer efficiency in oxygenators. To fill this gap, we extend our previously developed 1D mathematical model into a 3D computational framework to predict both blood pressure drops and the rates of oxygen and CO₂ transfers in oxygenators. The comparison between our model predictions and experimental data validates the model’s capability in capturing the overall trends in CO₂ transfer/removal rates under different sweep gas flow rates. The results also demonstrated that our model can predict CO₂ removal more accurately, particularly in scenarios where adjusting the sweep gas flow rate is essential for optimizing the oxygenator performance. Full article

(This article belongs to the Special Issue Respiratory Flows)

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19 pages, 4065 KiB

Open AccessArticle

Research on the Flow Mechanism of a Large-Scale Wind Turbine Blade Based on Trailing Edge Flaps

by Yifan Liu, Mingming Zhang, Bingfu Zhang, Haikun Jia, Na Zhao and Zhaohuan Zhang

Fluids 2025, 10(6), 157; https://doi.org/10.3390/fluids10060157 - 14 Jun 2025

Viewed by 282

Abstract

This study was performed based on the previous work of this research group to promote the practical engineering application of trailing edge flaps. Specifically, the established “intelligent blade” simulation platform was used for simulation calculations, bringing about the achievement of a significant load [...] Read more.

This study was performed based on the previous work of this research group to promote the practical engineering application of trailing edge flaps. Specifically, the established “intelligent blade” simulation platform was used for simulation calculations, bringing about the achievement of a significant load reduction effect in which the standard deviation of the blade root pitching moment decreased by 12.4% under the influence of the trailing edge flap. Then, the dynamic conditions of the wind turbine and trailing edge flap under active control, obtained from the “intelligent blade” simulation platform, were input into CFD for further high-fidelity simulations. Additionally, a simulation method that allows for the real-time observation of the flow field was optimized with CFD as a flow field visualizer. This approach assisted in analyzing how the trailing edge flap affects the flow characteristics around the blade. The results reveal that the deflection of the trailing edge flap generated new vortex structures. These new vortex structures interacted with the pre-existing vortex structures. Moreover, the vortex structures produced by flap deflection supplemented the energy dissipation caused by flow separation on the leeward surface of the blade, contributing to the weakening of flow separation on the leeward side of the blade, affecting the pressure exerted by the fluid on the blade surface, and ultimately lowering the blade’s load. Full article

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

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16 pages, 281 KiB

Open AccessArticle

Lighthill’s Theory of Sound Generation in Non-Isothermal and Turbulent Fluids

by Swati Routh and Zdzislaw E. Musielak

Fluids 2025, 10(6), 156; https://doi.org/10.3390/fluids10060156 - 13 Jun 2025

Viewed by 325

Abstract

Lighthill’s theory of sound generation was developed to calculate acoustic radiation from a narrow region of turbulent flow embedded in an infinite homogeneous fluid. The theory is extended to include a simple model of non-isothermal fluid that allows finding analytical solutions. The effects [...] Read more.

Lighthill’s theory of sound generation was developed to calculate acoustic radiation from a narrow region of turbulent flow embedded in an infinite homogeneous fluid. The theory is extended to include a simple model of non-isothermal fluid that allows finding analytical solutions. The effects of one specific temperature gradient on the wave generation and propagation are studied. It is shown that the presence of the temperature gradient in the region of wave generation leads to monopole and dipole sources of acoustic emission and that the efficiency of these two sources may be higher than Lighthill’s quadrupoles. In addition, the wave propagation far from the source is different than in Lighthill’s original work because of the presence of the acoustic cutoff frequency resulting from the temperature gradient. Full article

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

19 pages, 3072 KiB

Open AccessArticle

Ground Clearance Effects on the Aerodynamic Loading of Tilted Flat Plates in Tandem

by Dimitrios Mathioulakis, Nikolaos Vasilikos, Panagiotis Kapiris and Christina Georgantopoulou

Fluids 2025, 10(6), 155; https://doi.org/10.3390/fluids10060155 - 12 Jun 2025

Viewed by 392

Abstract

The aerodynamic loading of four as well as of six tilted flat plates-panels arranged in tandem and in close proximity to the ground is examined through force and pressure measurements. In the four-plate set up, conducted in an open-circuit wind tunnel, a movable [...] Read more.

The aerodynamic loading of four as well as of six tilted flat plates-panels arranged in tandem and in close proximity to the ground is examined through force and pressure measurements. In the four-plate set up, conducted in an open-circuit wind tunnel, a movable floor is used to vary the ground clearance, and a one-component force balance is employed to measure the drag coefficient Cd of each plate for tilt angles 10° to 90° and for two head-on wind directions, 0° and 180°. An increase in the ground clearance from 20% to 60% of the plates’ chord length, results in a Cd increase of over 40% in the downstream plates, and up to 20% in the leading one. For tilt angles below 40°, the drag on the first plate is up to 25% higher under the 180° wind direction compared to the opposite direction. Pressure distributions are also presented on a series of six much larger plates, examined in a closed-circuit wind tunnel at tilt angles ±30°. While the windward surfaces exhibit relatively uniform pressure distributions, regions of low pressure develop on their suction side, near the plates’ tips leading edge, tending to become uniform streamwise. Full article

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19 pages, 3128 KiB

Open AccessArticle

Slow Translation and Rotation of a Composite Sphere Parallel to One or Two Planar Walls

by Yu F. Chou and Huan J. Keh

Fluids 2025, 10(6), 154; https://doi.org/10.3390/fluids10060154 - 12 Jun 2025

Viewed by 644

Abstract

A semi-analytical investigation is conducted to examine the coupled translational and rotational motions of a composite spherical particle (consisting of an impermeable hard core surrounded by a permeable porous shell) immersed in a viscous fluid parallel to one or two planar boundaries under [...] Read more.

A semi-analytical investigation is conducted to examine the coupled translational and rotational motions of a composite spherical particle (consisting of an impermeable hard core surrounded by a permeable porous shell) immersed in a viscous fluid parallel to one or two planar boundaries under the steady condition of a low Reynolds number. The fluid flow is described using the Stokes equations outside the porous shell and the Brinkman equation within it. A general solution is formulated by employing fundamental solutions in both spherical and Cartesian coordinate systems. The boundary conditions on the planar walls are implemented using the Fourier transform method, while those on the inner and outer boundaries of the porous shell are applied via a collocation technique. Numerical calculations yield hydrodynamic force and torque results with good convergence across a broad range of physical parameters. For validation, the results corresponding to an impermeable hard sphere parallel to one or two planar walls are shown to be in close agreement with established solutions from the literature. The hydrodynamic drag force and torque experienced by the composite particle increase steadily with larger values of the ratio of the particle radius to the porous shell’s permeation length, the ratio of the core radius to the total particle radius, and the separations between the particle and the walls. It has been observed that the influence of the walls on translational motion is significantly stronger than that on rotational motion. When comparing motions parallel versus normal to the walls, the planar boundaries impose weaker hydrodynamic forces but stronger torques during parallel motions. The coupling between the translation and rotation of the composite sphere parallel to the walls exhibits complex behavior that does not vary monotonically with changes in system parameters. Full article

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

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19 pages, 4870 KiB

Open AccessArticle

Influence of an Air Slit in Dust Shields on Accumulation of Dust over PV Panels

by Ahmed M. Gobran, Mohamed S. Abd-Elhady and Hamdy A. Kandil

Fluids 2025, 10(6), 153; https://doi.org/10.3390/fluids10060153 - 10 Jun 2025

Viewed by 557

Abstract

Dust accumulation on Photovoltaic (PV) panels represents a major challenge for the operation of panels. There are several passive dust mitigation techniques, such as using a dust shield whose performance has been enhanced by integrating it with an air nozzle. The air exiting [...] Read more.

Dust accumulation on Photovoltaic (PV) panels represents a major challenge for the operation of panels. There are several passive dust mitigation techniques, such as using a dust shield whose performance has been enhanced by integrating it with an air nozzle. The air exiting the nozzle acts as an air barrier that obstructs the approach of dust particles to the panel’s surface. The objective of this study is to minimize dust accumulation over PV panels by adding slits within the dust shield. The function of the slit is to induce air drafts that can sweep dust away from the surface of the PV panel. Numerical simulations are performed to determine the influence of the slit size and position on dust mitigation. It has been found that there is a critical slit size, such that the deposition of particles for slits of sizes smaller or larger than that size decreases. Increasing the slit size increases dust deposition until a certain limit, i.e., the critical size, and that is due to the Coanda effect that keeps the flow intact with the shield until it reaches the panels’ surface, which increases the dust accumulation rate. On the other hand, increasing the slit size above the critical size decreases the dust deposition due to the change from a non-inertial flow to an inertial flow, which diverts the incoming particles from reaching the panels’ surface. Also, it has been found that keeping the slit location away from the panel’s surface decreases the accumulation of dust over the panels’ surface. Therefore, based on the performed simulations, the slit size should always be either greater or smaller than the critical size and as far as possible from the panel’s surface to minimize dust accumulation over PV panels. Full article

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

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25 pages, 6637 KiB

Open AccessArticle

Influence of Gurney Flap and Leading-Edge/Trailing-Edge Flaps on the Stall Characteristics and Aeroacoustic Performance of Airfoils

by Zelin Liu, Kaidi Li and Xiaojing Sun

Fluids 2025, 10(6), 152; https://doi.org/10.3390/fluids10060152 - 9 Jun 2025

Viewed by 848

Abstract

In aerospace, flow control techniques have improved the separation flow characteristics around airfoils by various means. In this paper, the delayed detached eddy simulation (DDES) technique is used to simulate the detailed flow field around the NACA0021 airfoil with two different flow control [...] Read more.

In aerospace, flow control techniques have improved the separation flow characteristics around airfoils by various means. In this paper, the delayed detached eddy simulation (DDES) technique is used to simulate the detailed flow field around the NACA0021 airfoil with two different flow control methods (Gurney flaps and leading- and trailing-edge flaps) applied at an angle of attack of 20°. The aerodynamic characteristics around the airfoil under these two flow control methods are investigated, and the results show that both flow control methods lead to a significant increase in the pressure on the suction surface of the airfoil, which contributes to an increase in lift. The aeroacoustic characteristics of the original airfoil, the Gurney flapped airfoil and the airfoil with leading-edge and trailing-edge flaps are then analyzed using a combination of DDES and FW-H acoustic analog equations. The results show that the total sound pressure level of the Gurney flap airfoil and the leading-edge and trailing-edge flap airfoil are improved in most azimuthal angles of the acoustic pointing distribution, among which the degree of improvement of the leading-edge and trailing-edge flap airfoil is greater than that of the Gurney flap airfoil near the trailing edge, and the total sound pressure level of the band leading- and trailing-edge flap airfoil decreases in the azimuthal angles near the leading edge. Compared with the original airfoil, the noise value is thus reduced by up to 4.13 dB. The results of pressure pulsation cloud map, sound pressure level cloud map on the airfoil surface and vortex cloud map distribution show that the two flow controls increase the pressure pulsation near the trailing edge, the range and peak value of sound emission on the airfoil surface increase, and the trailing vortex becomes more finely grained, which leads to an increase in noise. Full article

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

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18 pages, 1603 KiB

Open AccessArticle

On Modeling Laminar Flow Through Variable Permeability Transition Layer

by M. S. Abu Zaytoon and M. H. Hamdan

Fluids 2025, 10(6), 151; https://doi.org/10.3390/fluids10060151 - 9 Jun 2025

Viewed by 720

Abstract

A generalized model of the variable permeability in the transition layer is introduced in this work. This model can handle flows with a small Darcy number and might be useful in controlling permeability amplifications. A solution method for the resulting inhomogeneous, generalized Airy [...] Read more.

A generalized model of the variable permeability in the transition layer is introduced in this work. This model can handle flows with a small Darcy number and might be useful in controlling permeability amplifications. A solution method for the resulting inhomogeneous, generalized Airy equation is presented, together with a computational procedure for evaluating the generalized Airy functions and the generalized Nield–Kuznetsov function of the first kind. A complete solution is then provided for the tri-layer flow problem that involves flow over a porous layer with an embedded transition layer. Full article

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14 pages, 2313 KiB

Open AccessArticle

Ultrasound-Assisted Melt Extrusion of Polymers with the Main Harmonics of 10–60 kHz

by Diana Agüero-Valdez, Alain González-Sánchez, María Teresa Rodríguez-Hernández, Heidi Andrea Fonseca-Florido, Juan Guillermo Martínez-Colunga, Janett Anaid Valdez-Garza, Gilberto Francisco Hurtado-López, Víctor Javier Cruz-Delgado and Carlos Alberto Ávila-Orta

Fluids 2025, 10(6), 150; https://doi.org/10.3390/fluids10060150 - 5 Jun 2025

Viewed by 518

Abstract

Using a digital oscilloscope, the main harmonics resulting from the application of different frequencies and power levels of ultrasonic waves during the polymer extrusion process were identified. The primary harmonics are located between 10 and 60 kHz and exhibit unique characteristics, such as [...] Read more.

Using a digital oscilloscope, the main harmonics resulting from the application of different frequencies and power levels of ultrasonic waves during the polymer extrusion process were identified. The primary harmonics are located between 10 and 60 kHz and exhibit unique characteristics, such as shape, crest, and trough, the latter being associated with voltage and current. The crest-to-trough distance (height) observed during processing at 34 kHz and 375 W shows the highest value, which correlates with the highest melt flow index and the lowest apparent viscosity. It is well known that the application of ultrasonic waves can randomly break C-C bonds in hydrocarbon compounds, leading to a decrease in molecular weight. However, the application of ultrasonic waves at different frequencies and power levels can promote chain scission in both high- and medium-molecular-weight polymer chains, thereby increasing the molecular weight distribution. This phenomenon can lead to chain disentanglement, along with chain scission, as evidenced by a decrease in molecular weight at medium power and frequency intensities. Finally, a schematic representation of the interaction between polymer chains and ultrasonic waves is proposed. Full article

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5 pages, 159 KiB

Open AccessEditorial

Special Issue: Pipe Flow: Research and Applications, First Edition

by Leonardo Di G. Sigalotti

Fluids 2025, 10(6), 149; https://doi.org/10.3390/fluids10060149 - 3 Jun 2025

Viewed by 672

Abstract

The transport of fluids through pipes and channels is a foundational topic in fluid mechanics, with direct applications spanning many branches of science and engineering [...] Full article

(This article belongs to the Special Issue Pipe Flow: Research and Applications)

16 pages, 1776 KiB

Open AccessArticle

Simulation Analysis and Experimental Study of Pipeline Gas Resistance Modelling and Series Characteristics

by Shengzhe Ye, Xiaoyan Shen, Hao Zhang and Xintong Liu

Fluids 2025, 10(6), 148; https://doi.org/10.3390/fluids10060148 - 1 Jun 2025

Viewed by 663

Abstract

The principle of electro-analogy analysis treats a gas path structure as analogous to a circuit, offering significant potential for performance analysis in aerostatic systems. However, research on gas resistance remains in an early stage. This study investigates pipe gas resistance and its series [...] Read more.

The principle of electro-analogy analysis treats a gas path structure as analogous to a circuit, offering significant potential for performance analysis in aerostatic systems. However, research on gas resistance remains in an early stage. This study investigates pipe gas resistance and its series characteristics using a slender circular pipe as the subject. First, gas resistance is redefined based on a derivation of the Bernoulli equation, resulting in formulas covering low and high speeds and a calculation model for series gas resistance. Simulations are conducted to model the pipe, focusing on the coefficient of frictional resistance at low speeds. The results provide insights into the gas resistance of pipes with varying inner diameters and related series connections. An experiment is conducted to validate predictions, indicating that, at low speeds, the defined and determined gas resistance values for pipelines with inner diameters ranging from 1 to 6 mm are largely consistent. Both gas and series gas resistances decrease as the pressure difference between the two pipe ends increases. Relative errors below 5% are typically regarded as very good, especially when dealing with complex systems. The maximum relative error between the experimentally measured single gas resistance, based on the defining formula and the simulation value, is 3.1%. Furthermore, the maximum relative errors for the measured single and series gas resistance values are 5% and 3.8%, respectively, according to the defining and determining formulas. The theoretical model is effective and reliable, providing valuable theoretical support for impedance analysis of aerostatic systems. Full article

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19 pages, 3372 KiB

Open AccessReview

A Comprehensive Review of Biomass Gasification Characteristics in Fluidized Bed Reactors: Progress, Challenges, and Future Directions

by Lu Wang, Tuo Zhou, Bo Hou, Hairui Yang, Nan Hu and Man Zhang

Fluids 2025, 10(6), 147; https://doi.org/10.3390/fluids10060147 - 1 Jun 2025

Cited by 1 | Viewed by 1629

Abstract

Biomass fluidized bed gasification technology has attracted significant attention due to its high efficiency and clean energy conversion capabilities. However, its industrial application has been limited by insufficient technological maturity. This paper systematically reviews the research progress on biomass fluidized bed gasification characteristics; [...] Read more.

Biomass fluidized bed gasification technology has attracted significant attention due to its high efficiency and clean energy conversion capabilities. However, its industrial application has been limited by insufficient technological maturity. This paper systematically reviews the research progress on biomass fluidized bed gasification characteristics; compares the applicability of bubbling fluidized beds (BFBs), circulating fluidized beds (CFBs), and dual fluidized beds (DFBs); and highlights the comprehensive advantages of CFBs in large-scale production and tar control. The gas–solid flow characteristics within CFB reactors are highly complex, with factors such as fluidization velocity, gas–solid mixing homogeneity, gas residence time, and particle size distribution directly affecting syngas composition. However, experimental studies have predominantly focused on small-scale setups, failing to characterize the impact of flow dynamics on gasification reactions. Therefore, numerical simulation has become essential for in-depth exploration. Additionally, this study analyzes the influence of different gasification agents (air, oxygen-enriched, oxygen–steam, etc.) on syngas quality. The results demonstrate that oxygen–steam gasification eliminates nitrogen dilution, optimizes reaction kinetics, and significantly enhances syngas quality and hydrogen yield, providing favorable conditions for downstream processes such as green methanol synthesis. Based on the current research landscape, this paper employs numerical simulation to investigate oxygen–steam CFB gasification at a pilot scale (500 kg/h biomass throughput). The results reveal that under conditions of O₂/H₂O = 0.25 and 800 °C, the syngas H₂ volume fraction reaches 43.7%, with a carbon conversion rate exceeding 90%. These findings provide theoretical support for the industrial application of oxygen–steam CFB gasification technology. Full article

(This article belongs to the Special Issue Feature Reviews for Fluids 2025–2026)

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18 pages, 6982 KiB

Open AccessArticle

Digital Twins: A Solution Under the Standard k-ε Model in Industrial CFD, to Predict Ideal Conditions in a Sugar Dryer

by Verónica Guerrero-Hernández, Guillermo Reyes-Morales, Violeta Alejandra Bastián Lima, Jorge Ortega-Moody, Quelbis Román Quintero Bertel, Gerardo Aguila Rodríguez, Blanca Estela González Sánchez, Claudia Ceballos-Díaz and Luis Carlos Sandoval Herazo

Fluids 2025, 10(6), 146; https://doi.org/10.3390/fluids10060146 - 1 Jun 2025

Viewed by 807

Abstract

Currently, emerging technologies such as digital twins, through the application of frontier techniques, have achieved physics-based simulations that reduce time and costs. Hence, its application is of the utmost importance in the industry, mainly in the sugar drying process of sugar mills for [...] Read more.

Currently, emerging technologies such as digital twins, through the application of frontier techniques, have achieved physics-based simulations that reduce time and costs. Hence, its application is of the utmost importance in the industry, mainly in the sugar drying process of sugar mills for an updated version of the process. Sugar mills lack process control, leading to unexpected issues. Sugar mills with poor process control cause operational problems. This article presents significant innovation in the field of industrial process optimisation through the integration of digital twins with the k-ε standard model in computational fluid dynamics (CFD). The primary objective of this publication is to predict the ideal conditions of a centrifugal sugar dryer using CFD through the k-ε standard model to analyse the aerodynamic behaviour of the ambient air by applying heat through heat exchangers to obtain a suitable mass flow. The mathematical model was carried out under an energy balance to the thermodynamic system to study the behaviour through a simulation in MATLAB R2017 and an air-fluid simulation of drying with software CFD 2015. The results proved that the model of the thermal system and frontier conditions, when applying CFD, carried our simulation and remained stable. The ideal operating conditions of the centrifugal sugar dryer can be predicted effectively, with an energy saving of 4.25%. Full article

(This article belongs to the Special Issue Industrial CFD and Fluid Modelling in Engineering, 3rd Edition)

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18 pages, 3596 KiB

Open AccessArticle

Boundary Layer Separation from a Curved Backward-Facing Step Using Improved Delayed Detached-Eddy Simulation

by Matthew R. McConnell, Jason Knight and James M. Buick

Fluids 2025, 10(6), 145; https://doi.org/10.3390/fluids10060145 - 31 May 2025

Viewed by 902

Abstract

Curved surfaces are a feature of many engineering applications, and as such, the accurate prediction of separation and reattachment from a curved surface is of great engineering importance. In this study, improved delayed detached eddy simulation (IDDES) is used, in conjunction with synthetic [...] Read more.

Curved surfaces are a feature of many engineering applications, and as such, the accurate prediction of separation and reattachment from a curved surface is of great engineering importance. In this study, improved delayed detached eddy simulation (IDDES) is used, in conjunction with synthetic turbulence injection using the synthetic eddy method (SEM), to investigate the boundary layer separation from a curved backward-facing step for which large eddy simulation (LES) results are available. The commercial code Star CCM+ was used with the k-ω shear stress transport (SST) variation of the IDDES model to assess the accuracy of the code for this class of problem. The IDDES model predicted the separation length within 10.4% of the LES value for the finest mesh and 25.5% for the coarsest mesh, compared to 36.2% for the RANS simulation. Good agreement between the IDDES and LES was also found in terms of the distribution of skin friction, velocity, and Reynolds stress, demonstrating an acceptable level of accuracy, as has the prediction of the separation and reattachment location. The model has, however, found it difficult to capture the pressure coefficient accurately in the region of separation and reattachment. Overall, the IDDES model has performed well against a type of geometry that is typically a challenge to the hybrid RANS-LES method (HRLM). Full article

(This article belongs to the Special Issue Industrial CFD and Fluid Modelling in Engineering, 3rd Edition)

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13 pages, 1910 KiB

Open AccessArticle

Excellent Superhydrophobic Cone-Array Surfaces with Low Contact Time of Droplet Pancake Bouncing Under Various Conditions

by Yuanjie Chen, Yucai Lin, Shile Feng and Yongmei Zheng

Fluids 2025, 10(6), 144; https://doi.org/10.3390/fluids10060144 - 28 May 2025

Viewed by 468

Abstract

Superhydrophobic surfaces with a low liquid–solid contact time have huge application prospects in anti-icing, corrosion-resistant, self-cleaning, etc. Significant attempts have been devoted to reducing the contact time through altering the hydrodynamics of the process through which the droplet contacts the superhydrophobic surface. However, [...] Read more.

Superhydrophobic surfaces with a low liquid–solid contact time have huge application prospects in anti-icing, corrosion-resistant, self-cleaning, etc. Significant attempts have been devoted to reducing the contact time through altering the hydrodynamics of the process through which the droplet contacts the superhydrophobic surface. However, these works are rarely considered to be related to the influence of environmental conditions (e.g., the pH of the droplet, salinity of the droplet, droplet viscosity, and supercooled droplet impact). Here, we report various superhydrophobic cone arrays (SCAs) with low droplet impact contact times under various conditions (pH of the droplet, salinity of the droplet, droplet viscosity, droplet temperature, etc.). We demonstrate that the low contact time of the droplet impacting cone-arrays can be optimized via the critical Weber number, pillar-to-pillar spacing, and pillar height (e.g., 11.1, 350 μm, and 300 μm, respectively). The lowest droplet contact time of ~6 ms, which is reduced by more than 60% compared to conventional bouncing, can be achieved. In addition, directional pancake bouncing behaviors can achieve the largest horizontal displacement (85% of the droplet size, ~3 mm) on a tilted SCA with optimal tilt angles. These findings offer insights into the interface effect for controlling wetting that would extend the practical applications, e.g., liquid repellency, anti-corrosion, anti-icing, heat transfer, etc. Full article

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

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22 pages, 7959 KiB

Open AccessArticle

Numerical Investigation of Transitional Oscillatory Boundary Layers: Turbulence Quantities

by Selman Baysal and V. S. Ozgur Kirca

Fluids 2025, 10(6), 143; https://doi.org/10.3390/fluids10060143 - 28 May 2025

Viewed by 822

Abstract

This study investigates the organized flow structures and turbulence quantities in a transitional oscillatory boundary-layer flow over a smooth bed using a DNS model set up by the open-source framework Nektar++ (v5.2.0). The present model was validated against the results of a previous [...] Read more.

This study investigates the organized flow structures and turbulence quantities in a transitional oscillatory boundary-layer flow over a smooth bed using a DNS model set up by the open-source framework Nektar++ (v5.2.0). The present model was validated against the results of a previous study involving a bypass transition mechanism in the intermittently turbulent regime. To trigger the initial perturbations, a roughness element was placed on the bed and removed at the very moment a two-dimensional vortex tube, caused by an inflectional-point shear-layer instability, was observed on it. Then, the turbulent spots where the flow experienced intense fluctuations in an otherwise laminar boundary layer were identified from the bed shear-stress distribution on the bed, which served as a reliable indicator of turbulence. These flow features emerged as the first sign of the initiation of turbulence. Several measurement points were selected to follow the bed shear-stress variations and to observe the spatial and temporal development of turbulent spots at a low-wave Reynolds number,

R e = 1.8 \times 10^{5}

. Along with these observations, phase-resolved turbulence quantities were also investigated over successive half-cycles for the first time in the literature to understand how turbulence develops and spreads over the flow domain. The results show that the turbulence generated in the near-bed region becomes stronger in the deceleration stage due to the adverse pressure gradient and diffuses away from the bed during the subsequent phases of the developing oscillatory boundary-layer flow. The findings related to the turbulence quantities also indicate that the turbulence gradually evolves and spreads into the fluid domain in successive half-cycles. Full article

(This article belongs to the Section Turbulence)

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18 pages, 3611 KiB

Open AccessArticle

Development of an Anisotropic Porous Model of a Single Cow for Numerical Barn Simulations—A Numerical Study

by Julian Hartje

Fluids 2025, 10(6), 142; https://doi.org/10.3390/fluids10060142 - 27 May 2025

Viewed by 847

Abstract

Computational fluid dynamics (CFD) can be used to analyze the airflow patterns within a naturally ventilated cattle barn in detail, taking into account the influence of the animals. Typically, animals are modelled either as solid obstacles or as a porous block representing the [...] Read more.

Computational fluid dynamics (CFD) can be used to analyze the airflow patterns within a naturally ventilated cattle barn in detail, taking into account the influence of the animals. Typically, animals are modelled either as solid obstacles or as a porous block representing the entire animal-occupied zone (AOZ). In the latter approach, extensive pre-simulations are required to determine the appropriate resistance parameters. This study developed a cow model that captures the general influence of the animals, is easy to implement without the need for extensive pre-simulations, and can be applied to various barn types and herd sizes. It is based on a porous block for a single animal. The anisotropic parameters for pressure drop and heat flux were derived from a simplified 3D cow model under different wind speeds, flow directions, cow positions, and ambient temperatures. These parameters were then incorporated into the newly developed porous cow model using regression curves. A comparison between the solid and porous modelling approaches in a randomly selected AOZ showed good agreement in terms of pressure drop and downstream temperature distribution. Full article

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

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29 pages, 10025 KiB

Open AccessArticle

A Comprehensive Numerical and Experimental Study on Improving the Thermal Performance of a Shell and Helically Coiled Heat Exchanger Utilizing Hybrid Magnetic Nanofluids and Porous Spiral-Type Fins

by Ahmet Yağız Bacak, Ataollah Khanlari, Azim Doğuş Tuncer, Adnan Sözen, Halil İbrahim Variyenli and Kambiz Vafai

Fluids 2025, 10(6), 141; https://doi.org/10.3390/fluids10060141 - 27 May 2025

Viewed by 1156

Abstract

In this work, a novel type of shell and helically coiled heat exchangers (SHCHEXs) that are used extensively in numerous applications has been numerically and experimentally studied. A low-cost and easily applicable design for enhancing the heat exchange rate in a shell and [...] Read more.

In this work, a novel type of shell and helically coiled heat exchangers (SHCHEXs) that are used extensively in numerous applications has been numerically and experimentally studied. A low-cost and easily applicable design for enhancing the heat exchange rate in a shell and helically coiled heat exchanger has been developed within the scope of this study. In this context, a SHCHEX has been developed with an internal guiding pipe and spirally formed fins with the purpose of leading the fluid in the cold loop over the coil where hot fluid flows inside it. Numerical simulations were carried out in this study for determining how the new changes including nonporous and porous spiral fins affected heat transfer in the system. In the experimental part of the current research, a heat exchanger with a guiding pipe and nonporous spiral fins has been fabricated and its thermal behavior tested at various conditions utilizing water and MnFe₂O₄-ZnFe₂O₄/water hybrid-type nanofluid. Both numerical and experimental findings of this research exhibited positive effects of using new modifications including spiral fin integration. Overall findings of this work clearly exhibited a significant effect of the spiral fin medication and MnFe₂O₄-ZnFe₂O₄/water-hybrid magnetic nanofluid utilization on the thermal performance improvement in the heat exchanger. Experimentally determined findings showed that using MnFe₂O₄-ZnFe₂O₄/water in the hot loop of the SHCHEX improved the heat transfer coefficient of the heat exchanger by an average ratio of 16.2%. In addition, mean variation between the experimentally obtained exit temperature and numerically achieved one was 3.9%. Full article

(This article belongs to the Collection Challenges and Advances in Heat and Mass Transfer)

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18 pages, 1959 KiB

Open AccessReview

Modelling Water Waves on Graphs

by André Nachbin

Fluids 2025, 10(6), 140; https://doi.org/10.3390/fluids10060140 - 24 May 2025

Viewed by 633

Abstract

Waves on graphs are a current subject of research interest. As opposed to flows on graphs, the reflection–transmission of waves at the graph’s vertex is a problem that needs to be further modelled mathematically. The literature on the reflection and transmission of waves [...] Read more.

Waves on graphs are a current subject of research interest. As opposed to flows on graphs, the reflection–transmission of waves at the graph’s vertex is a problem that needs to be further modelled mathematically. The literature on the reflection and transmission of waves at a vertex is scarce. Some articles are reviewed and discussed. Water waves are a good topic for comparing different mathematical models, from hyperbolic conservation laws to weakly nonlinear, weakly dispersive systems of partial differential equations on a two-dimensional fattened (thick) graph and the respective one-dimensional graph-model reduction. In this study, we present a particular water wave model in which junction angles are systematically included in the mathematical model. Comparing the solutions with the fattened-graph model gave rise to a more general compatibility condition at the vertex. Current research topics of interest are outlined at the end. Full article

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

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Fluids, Volume 10, Issue 6 (June 2025) – 21 articles

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