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Indoor Air Quality Control for Airborne Diseases: A Review on Portable UV Air Purifiers
Simulating River Morphology Evolution Under Floodplain Vegetation Influence
An Analysis and Comparison of the Hydrodynamic Behavior of Ships Using Mesh-Based and Meshless Computational Fluid Dynamics Simulations
Literature Review on Single and Twin-Screw Extruders Design for Polymerization Using CFD Simulation
Fokker-Planck Central Moment Lattice Boltzmann Method for Effective Fluid Flow Simulations

Journal Description

Fluids

Fluids is an international, peer-reviewed, open access journal on all aspects of fluids, published monthly online by MDPI. The Portuguese Society of Rheology (SPR) is affiliated with Fluids and its members receive discounts on the article processing charges.

Open Access— free for readers, with article processing charges (APC) paid by authors or their institutions.
High Visibility: indexed within Scopus, ESCI (Web of Science), Inspec, CAPlus / SciFinder, and other databases.
Journal Rank: CiteScore - Q2 (Mechanical Engineering)
Rapid Publication: manuscripts are peer-reviewed and a first decision is provided to authors approximately 21.1 days after submission; acceptance to publication is undertaken in 3.6 days (median values for papers published in this journal in the second half of 2024).
Recognition of Reviewers: reviewers who provide timely, thorough peer-review reports receive vouchers entitling them to a discount on the APC of their next publication in any MDPI journal, in appreciation of the work done.

Impact Factor: 1.8 (2023); 5-Year Impact Factor: 1.8 (2023)

Imprint Information Journal Flyer Open Access ISSN: 2311-5521

Latest Articles

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 (registering DOI) - 4 Apr 2025

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)

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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 (registering DOI) - 3 Apr 2025

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)

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35 pages, 3651 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 (registering DOI) - 3 Apr 2025

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)

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

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

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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

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

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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

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)

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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

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)

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Graphical abstract

48 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

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

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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

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)

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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

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)

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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

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)

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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

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)

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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

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)

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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

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)

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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

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)

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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

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

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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

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

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)

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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

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

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12 pages, 1440 KiB

Open AccessArticle

Shear Number as a Practical Tool for Flow Regime Evaluation and Education

by Kazys Almenas, Stasys Gasiūnas, Marijus Šeporaitis and Raimondas Pabarčius

Fluids 2025, 10(4), 76; https://doi.org/10.3390/fluids10040076 - 22 Mar 2025

Turbulence is a complex and challenging concept, often simplified for students through the use of the Reynolds Number (Re), used to indicate when flow transitions from laminar to turbulent occurs. However, the Re number focus on the ratio of inertial to viscous forces [...] Read more.

Turbulence is a complex and challenging concept, often simplified for students through the use of the Reynolds Number (Re), used to indicate when flow transitions from laminar to turbulent occurs. However, the Re number focus on the ratio of inertial to viscous forces limits its ability to explain the physical mechanisms driving turbulence, particularly in cases involving different flow boundaries or two-phase stratified flows including flows with phase change. This article presents the development and reasoning of the Shear number (Sn) as a new turbulence indicator, based on the ratio of shear to viscous forces, which provides a more intuitive and accurate representation of turbulence initiation. By comparing Sn to Re, this study demonstrates how the Sn number enhances the understanding of turbulent flow and offers a more accessible tool for both teaching and practical applications in fluid dynamics. Full article

(This article belongs to the Section Turbulence)

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