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 20.8 days after submission; acceptance to publication is undertaken in 2.9 days (median values for papers published in this journal in the second half of 2025).
- 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 (2024);
5-Year Impact Factor:
1.9 (2024)
Latest Articles
Reverse Steady Streaming Induced by a Freely Moving Wavy Wall
Fluids 2026, 11(1), 27; https://doi.org/10.3390/fluids11010027 - 20 Jan 2026
Abstract
In this work, we present a theoretical and experimental investigation of the fluid–structure interaction between a freely moving wall and an oscillatory flow. Our objective is to elucidate the coupling mechanism between the fluid and the oscillating body that gives rise to reverse
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In this work, we present a theoretical and experimental investigation of the fluid–structure interaction between a freely moving wall and an oscillatory flow. Our objective is to elucidate the coupling mechanism between the fluid and the oscillating body that gives rise to reverse streaming, that is, the reversal in the rotation direction of the resulting steady vortices, and to apply this analysis to the case of a freely moving wavy wall. The flow is analyzed theoretically based on a two-dimensional model and an analytical solution is obtained using a perturbation method. Experimental results based on Particle Image Velocimetry are also presented, where an oscillatory flow generated by an electromagnetic force in an electrolyte layer drives a wavy wall floating on the surface. The results confirm the occurrence of reverse streaming and demonstrate that the flow dynamics depend on the density ratio between the freely moving solid and the fluid. The analytical solution qualitatively captures the streaming reversal observed in the experiments.
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(This article belongs to the Special Issue 10th Anniversary of Fluids—Recent Advances in Fluid Mechanics)
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Open AccessArticle
Three-Dimensional CFD Simulations of the Flow Around an Infinitely Long Cylinder from Subcritical to Postcritical Reynolds Regimes Using DES
by
Marielle de Oliveira, Fábio Saltara, Adrian Jackson, Mark Parsons and Bruno S. Carmo
Fluids 2026, 11(1), 26; https://doi.org/10.3390/fluids11010026 - 20 Jan 2026
Abstract
The flow around circular cylinders is a classic problem in fluid mechanics with significant implications for offshore engineering. While extensive numerical and experimental research has focused on the subcritical and critical Reynolds regimes, the supercritical and postcritical regimes remain challenging and relatively unexplored,
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The flow around circular cylinders is a classic problem in fluid mechanics with significant implications for offshore engineering. While extensive numerical and experimental research has focused on the subcritical and critical Reynolds regimes, the supercritical and postcritical regimes remain challenging and relatively unexplored, primarily due to the complex nature of turbulence and the high computational requirements. In this study, we perform three-dimensional detached eddy simulations using the finite volume method in OpenFOAM v1906, employing Menter’s k- SST turbulence model, to systematically investigate the flow past an infinitely long smooth cylinder from the subcritical through the postcritical regimes. The numerical setup ensures accurate near-wall resolution and reliable representation of unsteady flow features. We present a detailed analysis of vortex shedding patterns, wake evolution, and statistical properties of lift and drag coefficients for selected Reynolds numbers representative of each regime. The simulation results are benchmarked against experimental data from the literature, demonstrating good agreement for Strouhal number and mean drag. Special emphasis is placed on the evolution of wake topology and force coefficients as the flow transitions from laminar to fully turbulent conditions. The findings contribute to the limited numerical literature on flow around circular cylinders across subcritical, critical, supercritical, and postcritical Reynolds number regimes, providing insights that are fundamentally relevant to the broader scope of understanding vortex shedding phenomena.
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(This article belongs to the Section Mathematical and Computational Fluid Mechanics)
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Open AccessArticle
Viscoelastic Properties of Organosilicon Fluid Interlayer at Low-Frequency Shear Deformations
by
Tuyana Dembelova, Badma Badmaev, Aleksandr Mashanov, Dari Dembelova, Michael I. Ojovan and Migmar Darmaev
Fluids 2026, 11(1), 25; https://doi.org/10.3390/fluids11010025 - 19 Jan 2026
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The present work explores the viscoelastic properties of a homologous series of organosilicon fluids (polymethylsiloxane fluids) using the acoustic resonant method at a frequency of shear vibrations of approximately 100 kHz. The resonant method is based on investigating the influence of additional binding
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The present work explores the viscoelastic properties of a homologous series of organosilicon fluids (polymethylsiloxane fluids) using the acoustic resonant method at a frequency of shear vibrations of approximately 100 kHz. The resonant method is based on investigating the influence of additional binding forces on the resonant characteristics of the oscillatory system. The fluid under study was placed between a piezoelectric quartz crystal that performs tangential oscillations and a solid cover plate. Standing shear waves were established in the fluid. The thickness of the liquid layer was much smaller than the length of the shear wavelength, and low-amplitude deformations allowed for the determination of the complex shear modulus G* in the linear region, where the shear modulus has a constant value. The studies demonstrated the presence of a viscoelastic relaxation process at the experimental frequency, which is several orders of magnitude lower than the known high-frequency relaxation in liquids. In this work, the relaxation frequency of the viscoelastic process in the studied fluids and the effective viscosity were calculated, and the lengths of the shear wave and the attenuation coefficients were determined.
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Open AccessArticle
Premixed Flame Passage Through a Perforated Barrier in a Hele-Shaw Channel
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Sergey Yakush, Sergey Rashkovskiy, Maxim Alexeev and Oleg Semenov
Fluids 2026, 11(1), 24; https://doi.org/10.3390/fluids11010024 - 19 Jan 2026
Abstract
The passage of a premixed stoichiometric methane-air flame through a hole in an internal barrier in a Hele-Shaw channel with one end closed was studied experimentally. It was found that for the same initial conditions, a flame propagating from the closed channel end
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The passage of a premixed stoichiometric methane-air flame through a hole in an internal barrier in a Hele-Shaw channel with one end closed was studied experimentally. It was found that for the same initial conditions, a flame propagating from the closed channel end can either pass through the hole in the barrier or be extinguished. The passage probability dependence on the hole width was found to be non-monotonic, with a sharp maximum at small hole sizes, followed by a minimum at intermediate sizes and a gradual increase as the blockage ratio tends to zero. The nature of this non-monotonic behavior of flame passage probability was analyzed by analyzing the flame front histories leading to flame passage or extinction at the same experimental parameters. A likely cause of this behavior is the development of an alternating-direction gas jet blowing from the hole due to the pressure difference between the channel compartments. Cooling of hot combustion products with cold channel walls can cause a pressure drop in the closed channel part and development of a reverse (open-to-closed compartment) gas jet affecting the approaching flame. Therefore, flame passage or extinguishment is a feature of the whole two-chamber system, rather than an intrinsic flame property.
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(This article belongs to the Section Heat and Mass Transfer)
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Open AccessArticle
Turbulent Flow Analysis of a Representative Low-Height Urban Landscape in Mexico
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Cecilia Ibarra-Hernández, Luis Hernández-García, Rodolfo Nájera-Sanchez, Enriqueta Arriaga-Gomez, Sergio Martínez-Delgadillo, Diana Medellín-Salazar and Alejandro Alonzo García
Fluids 2026, 11(1), 23; https://doi.org/10.3390/fluids11010023 - 16 Jan 2026
Abstract
This article analyzes the applications of computational fluid dynamics (CFD) in addressing the issue of flow patterns in a realistic urban landscape, specifically in the Metropolitan Area of Monterrey. CFD enables the simulation of physical phenomena such as turbulence, which is useful for
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This article analyzes the applications of computational fluid dynamics (CFD) in addressing the issue of flow patterns in a realistic urban landscape, specifically in the Metropolitan Area of Monterrey. CFD enables the simulation of physical phenomena such as turbulence, which is useful for studying the transport behavior of pollutants in urban environments. The computational model was obtained from satellite imaging and covered a surface of about 1.134 km × 1.227 km. It was composed of 173 urban blocks, representing around 3570 houses, including hospitals, schools, recreation centers and other gathering places. The population of the urban landscape was estimated at around 11,400 inhabitants. Three velocity scenarios, low, average, and high (air gusts), were simulated, using data from a local weather station. The Reynolds numbers (Re) ranged from 1.9 × 106 to 21.2 × 106, falling within the fully developed turbulence regime, which was modeled using the renormalization group (RNG) k–ε turbulence model. Results showed that the mean velocity patterns were preserved independent of the Reynolds number (Re) and were characterized by regions of high velocity in the main avenues, as well as other regions of low velocity between urban blocks. This methodology may also be applicable for understanding the flow patterns of similar urban regions composed of irregularly arranged low-rise blocks.
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(This article belongs to the Special Issue CFD Applications in Environmental Engineering)
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Open AccessReview
Advancements in Synthetic Jet for Flow Control and Heat Transfer: A Comprehensive Review
by
Jangyadatta Pasa, Md. Mahbub Alam, Venugopal Arumuru, Huaying Chen and Tinghai Cheng
Fluids 2026, 11(1), 22; https://doi.org/10.3390/fluids11010022 - 14 Jan 2026
Abstract
Synthetic jets, generated through the periodic suction and ejection of fluid without net mass addition, offer distinct benefits, such as compactness, ease of integration, and independence from external fluid sources. These characteristics make them well-suited for flow control and convective heat transfer applications.
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Synthetic jets, generated through the periodic suction and ejection of fluid without net mass addition, offer distinct benefits, such as compactness, ease of integration, and independence from external fluid sources. These characteristics make them well-suited for flow control and convective heat transfer applications. However, conventional single-actuator configurations are constrained by limited jet formation, narrow surface coverage, and diminished effectiveness in the far field. This review critically evaluates the key limitations and explores four advanced configurations developed to mitigate them: dual-cavity synthetic jets, single-actuator multi-orifice jets, coaxial synthetic jets, and synthetic jet arrays. Dual-cavity synthetic jets enhance volume flow rate and surface coverage by generating multiple vortices and enabling jet vectoring, though they remain constrained by downstream vortex diffusion. Single-actuator multi-orifice designs enhance near-field heat transfer through multiple interacting vortices, yet far-field performance remains an issue. Coaxial synthetic jets improve vortex dynamics and overall performance but face challenges at high Reynolds numbers. Synthetic jet arrays with independently controlled actuators offer the greatest potential, enabling jet vectoring and focusing to enhance entrainment, expand spanwise coverage, and improve far-field performance. By examining key limitations and technological advances, this review lays the foundation for expanded use of synthetic jets in practical engineering applications.
Full article
(This article belongs to the Special Issue Feature Reviews for Fluids 2025–2026)
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Open AccessArticle
High-Speed Microprocessor-Based Optical Instrumentation for the Detection and Analysis of Hydrodynamic Cavitation Downstream of an Additively Manufactured Nozzle
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Luís Gustavo Macêdo West, André Jackson Ramos Simões, Leandro do Rozário Teixeira, Lucas Ramalho Oliveira, Juliane Grasiela de Carvalho Gomes, Igor Silva Moreira dos Anjos, Antonio Samuel Bacelar de Freitas Devesa, Leonardo Rafael Teixeira Cotrim Gomes, Lucas Gomes Pereira, Iran Eduardo Lima Neto, Júlio Cesar de Souza Inácio Gonçalves, Luiz Carlos Simões Soares Junior, Germano Pinto Guedes, Geydison Gonzaga Demetino, Marcus Vinícius Santos da Silva, Vitor Leão Filardi, Vitor Pinheiro Ferreira, André Luiz Andrade Simões, Luciano Matos Queiroz and Iuri Muniz Pepe
Fluids 2026, 11(1), 21; https://doi.org/10.3390/fluids11010021 - 14 Jan 2026
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This study presents the development and validation of a high-speed optical data acquisition system for detecting and characterizing hydrodynamic cavitation downstream of a triangular nozzle. The system integrates a PIN photodiode, a transimpedance amplifier, and a high-sampling-rate microcontroller. Its performance was first evaluated
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This study presents the development and validation of a high-speed optical data acquisition system for detecting and characterizing hydrodynamic cavitation downstream of a triangular nozzle. The system integrates a PIN photodiode, a transimpedance amplifier, and a high-sampling-rate microcontroller. Its performance was first evaluated using controlled sinusoidal signals, and statistical stability was assessed as a function of the number of acquired samples. Experiments were subsequently conducted in a converging–diverging conduit under biphasic flow conditions, where mean irradiance, standard deviation, and frequency spectra were analyzed downstream of the nozzle. The optical signal distributions revealed transitions in flow behavior associated with cavitation development, which were quantified through statistical metrics and spectral features. The Strouhal number was estimated from dominant frequencies extracted from the spectra, exhibiting a non-monotonic dependence on the Reynolds number, consistent with changes in flow structure and turbulence intensity. Spectral analysis further indicated frequency bands associated with energy transfer across turbulent scales and bubble dynamics. Overall, the results demonstrate that the proposed optical system constitutes a viable and non-intrusive methodology for detecting and characterizing cavitation intensity in a way that complements other optical and acoustic methods.
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Open AccessArticle
Ideas on New Fluid Dynamic Theory Based on the Liutex Rigid Rotation Definition
by
Kuncan Zheng, Zhi Pan, You Fan, Yiting Liu, Dapeng Zhang and Yonghong Niu
Fluids 2026, 11(1), 20; https://doi.org/10.3390/fluids11010020 - 12 Jan 2026
Abstract
In recent years, a novel decomposition of fluid motion has been proposed, which mathematically defines a type of fluid rigid rotation distinct from vorticity, termed the Liutex quantity. Since its introduction, Liutex has been successfully applied to describe fluid vortices and has emerged
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In recent years, a novel decomposition of fluid motion has been proposed, which mathematically defines a type of fluid rigid rotation distinct from vorticity, termed the Liutex quantity. Since its introduction, Liutex has been successfully applied to describe fluid vortices and has emerged as an internationally recognized third-generation vortex identification method. This new motion decomposition undoubtedly leads to a revised description of rotational and deformational motions, thereby necessitating a new description of dynamics. Therefore, based on the Stokes assumption and the novel Liutex decomposition, this paper constructs a new constitutive equation and derives a new set of fluid dynamic equations. The research findings reveal two key insights: first, the new shear stress in the fluid is no longer symmetric; second, in addition to traditional forces such as body force, pressure, and viscous force, an additional force induced by Liutex-based rigid rotation is identified. Furthermore, the new dynamic framework encompasses traditional fluid dynamics, with the latter being a special case when Liutex equals the traditional vorticity. It is anticipated that the proposed equations will find significant applications in the study of fluid vortices and turbulence and will undoubtedly stimulate research interest in the field of fluid mechanics.
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(This article belongs to the Special Issue Vortex Definition and Identification)
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Open AccessArticle
Turbulence After a Time-Periodic Change of Observer
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Arturo A. Arosemena, Rohith Jayaram and Jannike Solsvik
Fluids 2026, 11(1), 19; https://doi.org/10.3390/fluids11010019 - 10 Jan 2026
Abstract
Objectivity or material frame indifference is the indifference of material behavior to a Euclidean transformation (a general change of observer). This paper considers the objectivity of turbulent fields under a time-periodic change of the observer. At a given phase, the fluctuating velocity and
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Objectivity or material frame indifference is the indifference of material behavior to a Euclidean transformation (a general change of observer). This paper considers the objectivity of turbulent fields under a time-periodic change of the observer. At a given phase, the fluctuating velocity and Reynolds stress tensor fields are shown to be objective. This is further illustrated by presenting one-point statistics of two canonical flows: homogeneous isotropic turbulence and turbulent channel flow. The results also highlight that statistical symmetries such as homogeneity and stationarity found in the objective fields are carried over after a change of observer. The paper concludes with some final thoughts on objectivity and its usefulness for the advancement of turbulent theory.
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(This article belongs to the Section Turbulence)
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Spatial and Energetic Organization of Coherent Structures in Couette–Poiseuille Turbulent Channels
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Sergio Gandía-Barberá and Sergio Hoyas
Fluids 2026, 11(1), 18; https://doi.org/10.3390/fluids11010018 - 8 Jan 2026
Abstract
Coherent structures play a pivotal role in wall-bounded turbulence, serving as primary carriers of momentum, energy, and scalar quantities across the flow. This study examines coherent structures, specifically streamwise streaks and intense Reynolds stress regions (Q structures), within a novel DNS dataset capturing
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Coherent structures play a pivotal role in wall-bounded turbulence, serving as primary carriers of momentum, energy, and scalar quantities across the flow. This study examines coherent structures, specifically streamwise streaks and intense Reynolds stress regions (Q structures), within a novel DNS dataset capturing a stepped transition from pure Poiseuille flow to pure Couette flow at , based on the stationary wall. Structures are identified using a percolation algorithm to ensure well-defined boundaries, followed by three-dimensional clustering in Cartesian coordinates. They are further classified as wall-attached or wall-detached based on their proximity to the domain walls. Intense Reynolds stress structures are categorized into quadrants according to the signs of their averaged velocity components. The statistical properties of these structures—encompassing geometric characteristics, energy content, and spatial distribution—are thoroughly analyzed. Particular emphasis is placed on how these properties evolve across the transition from Poiseuille to Couette flow. The results reveal that increasing mean shear in Couette-like cases significantly influences the energy content and spatial distribution of the structures while their geometric characteristics remain relatively consistent across the dataset. This spatial distribution is closely linked to the large-scale structures of the streamwise velocity component in Couette flow, confirming that these structures are genuine physical features rather than artificial artifacts of the flow.
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(This article belongs to the Special Issue Modelling Flows in Pipes and Channels)
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Open AccessArticle
Solid–Liquid Flow Analysis Using Simultaneous Two-Phase PIV in a Stirred Tank Bioreactor
by
Mohamad Madani, Angélique Delafosse, Sébastien Calvo and Dominique Toye
Fluids 2026, 11(1), 17; https://doi.org/10.3390/fluids11010017 - 8 Jan 2026
Abstract
Solid–liquid stirred tanks are widely used in multiphase processes, including bioreactors for mesenchymal stem cell (MSC) culture, yet simultaneous experimental data for both dispersed and carrier phases remain limited. Here, a refractive index-matched (RIM) suspension of PMMA microparticles (
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Solid–liquid stirred tanks are widely used in multiphase processes, including bioreactors for mesenchymal stem cell (MSC) culture, yet simultaneous experimental data for both dispersed and carrier phases remain limited. Here, a refractive index-matched (RIM) suspension of PMMA microparticles ( , ) in an NH4SCN solution is studied at an intermediate Reynolds number ( ), low Stokes number ( ), and particle volume fractions v%. This system was previously established and studied for the effect of addition of particles on the carrier phase. In this work, a dual-camera PIV set-up provides simultaneous velocity fields of the liquid and particle phases in a stirred tank equipped with a three-blade down-pumping HTPGD impeller. The liquid mean flow and circulation loop remained essentially unchanged with particle loading, whereas particle mean velocities were lower than single-phase and liquid-phase values in the impeller discharge. Turbulence levels diverged between phases: liquid-phase turbulent kinetic energy (TKE) in the impeller region increased modestly with , while solid-phase TKE was attenuated. Slip velocity maps showed that particles lagged the fluid in the impeller jet and deviated faster from the wall in the upward flow, with slip magnitudes increasing with . An approximate axial force balance indicated that drag dominates over lift in the impeller and wall regions, while the balance is approximately satisfied in the tank bulk, providing an experimental benchmark for refining drag and lift models in this class of stirred tanks.
Full article
(This article belongs to the Special Issue Numerical Modeling and Experimental Studies of Two-Phase Flows, 2nd Edition)
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Modeling and Experimental Analysis of Low-Viscosity/High-Permeability Sealant Penetration Dynamics in Oil-Filled Submarine Cables
by
Zhao Zhang, Mingli Fu, Chang Cai, Linjie Zhao, Lei Jia, Baojun Hui, Shuai Hou and Ming Zhang
Fluids 2026, 11(1), 16; https://doi.org/10.3390/fluids11010016 - 5 Jan 2026
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Insulating oil leakage from oil-filled submarine cables compromised operational integrity and posed environmental risks. This study proposed a novel sealant-plugging repair technique that combines low-viscosity/high-permeability sealant permeation and high-viscosity/low-permeability sealant replacement and pressurization. The permeation process of the low-viscosity sealant, from the injection
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Insulating oil leakage from oil-filled submarine cables compromised operational integrity and posed environmental risks. This study proposed a novel sealant-plugging repair technique that combines low-viscosity/high-permeability sealant permeation and high-viscosity/low-permeability sealant replacement and pressurization. The permeation process of the low-viscosity sealant, from the injection port to the outlet, was visualized using the Volume of Fluid (VOF) method. Analysis focused on: (1) sealant volume fraction in the sealing cavity; (2) sealant leakage volume fraction along the radial gaps at outlet 2; and (3) relative velocity of the permeating sealant along the radial gaps at outlet 2. Application of 0.4 MPa of sealant pressure achieved the key balance, characterized by: (i) Completed displacement of air from the sealing cavity; (ii) Full permeation of sealant into the gaps between the armored copper strip gaps and the radial gaps; (iii) Avoidance of the excessive sealant leakage flow observed at 0.5 MPa, promoting efficient sealant usage; (iv) A short time to reach permeation and leakage steady state. This study demonstrated the feasibility of the low-viscosity sealant penetration into both the gaps between the armored copper strips and the radial gaps under 0.4 MPa injection pressure. It provided theoretical and experimental guidance for this process within the sealant plugging repair technique.
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Open AccessArticle
A Study on the Evolution of Flow Regime in a Gas-Assisted Submerged High-Pressure Water Jet
by
Hao Yan, Caixia Zhang, Wenhao Li and Ning Chen
Fluids 2026, 11(1), 15; https://doi.org/10.3390/fluids11010015 - 31 Dec 2025
Abstract
High-pressure water jet technology is widely utilized for cleaning marine artificial structures due to its portability, efficiency, and environmental friendliness, yet traditional jets underperform in submerged environments. Gas-assisted water jet technology has predominantly been applied to rock breaking—where vertical forces are prioritized—with insufficient
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High-pressure water jet technology is widely utilized for cleaning marine artificial structures due to its portability, efficiency, and environmental friendliness, yet traditional jets underperform in submerged environments. Gas-assisted water jet technology has predominantly been applied to rock breaking—where vertical forces are prioritized—with insufficient research into flow regime evolution, limiting its utility for cleaning applications. This study introduces a supercavitating high-pressure water jet aimed at improving underwater cleaning efficiency while lowering economic costs. Employing ANSYS Fluent—with the RNG k-ε turbulence model and mixture model—validated via high-speed camera experiments, we explored the flow regime evolution of both unconstrained and semi-constrained impinging jets. The key findings of this paper are as follows: The cavity evolves with a periodic “necking-bubbling” pattern, whose intensity correlates positively with gas outlet velocity and supply rate; moderate gas supply—with 120 L/min identified as optimal through orthogonal analysis—effectively delays water jet breakup. For semi-constrained jets, the wall-adjacent gas flow also exhibits “necking-bubbling”; small-angle impact (30° versus 60°) reduces near-wall shear vortices, enhancing gas cavity stability on the target plate. This study bridges the gap between gas-assisted jet technology and underwater cleaning requirements, offering theoretical insights and optimized parameters for efficient, low-cost marine structure cleaning. It thereby supports the sustainable exploitation of marine resources and the stable operation of key marine facilities.
Full article
(This article belongs to the Special Issue Cavitation and Bubble Dynamics, 2nd Edition)
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Open AccessReview
Recent Advances in Experimental and Numerical Studies on Cloud and Erosion Behaviors in Cavitating Jets
by
Nobuyuki Fujisawa
Fluids 2026, 11(1), 14; https://doi.org/10.3390/fluids11010014 - 31 Dec 2025
Abstract
Recent advances in experimental techniques for visualizing cloud behavior, pit formation, and erosion in cavitating jets have been reviewed. To characterize the erosion behavior of cavitating jets and clarify their erosion mechanisms, various experimental techniques—such as high-speed imaging, frame difference method, proper orthogonal
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Recent advances in experimental techniques for visualizing cloud behavior, pit formation, and erosion in cavitating jets have been reviewed. To characterize the erosion behavior of cavitating jets and clarify their erosion mechanisms, various experimental techniques—such as high-speed imaging, frame difference method, proper orthogonal decomposition (POD) analysis, pit sensors, polyvinylidene fluoride (PVDF) sensors, laser schlieren imaging, and cross schlieren imaging—have been developed. Experimental results demonstrated that the erosion mechanism of cavitating jets is highly correlated with periodic cloud behaviors, including the growth, shrinkage, and collapse, which generate impulsive pressure on the wall material. This pressure initiates random pits on the wall surface and is associated with the generation of microjets caused by the reentrant-jet mechanism during cloud collapse near the wall. Several shockwaves were generated at peak impulsive pressures when the cavitation cloud collapsed, and a microjet was formed. Some of these experimental findings were successfully reproduced in recent numerical studies; however, further numerical modeling of erosion behavior in cavitating jets is still needed. Furthermore, the behavior of cavitating jets on rough walls requires future study, as the erosion rate is significantly higher than that on smooth walls.
Full article
(This article belongs to the Special Issue Feature Reviews for Fluids 2025–2026)
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Open AccessArticle
Transient Electrophoresis in Suspensions of Charged Porous Particles
by
Wei Z. Chen and Huan J. Keh
Fluids 2026, 11(1), 13; https://doi.org/10.3390/fluids11010013 - 30 Dec 2025
Abstract
The start-up of electrophoretic motion in a suspension of uniformly charged, porous, spherical particles within an arbitrary electrolyte solution under a suddenly applied electric field is investigated. The unsteady Stokes/Brinkman equations, modified to include the electric body force, are solved for the fluid
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The start-up of electrophoretic motion in a suspension of uniformly charged, porous, spherical particles within an arbitrary electrolyte solution under a suddenly applied electric field is investigated. The unsteady Stokes/Brinkman equations, modified to include the electric body force, are solved for the fluid velocity field using a unit cell model to account for the particle-particle interactions. An explicit expression for the transient electrophoretic velocity of a porous particle in a unit cell is derived in the Laplace transform domain as a function of the key governing parameters. The transient electrophoretic velocity, when normalized by its steady-state counterpart, increases monotonically with both elapsed time and the ratio of particle radius to Debye length, with other parameters held constant. It generally increases with the ratio of particle radius to permeation length and with porosity, while decreasing monotonically with an increase in the particle-to-fluid density ratio. Similar to its steady-state value, the transient electrophoretic mobility of the suspension is typically a decreasing function of the particle volume fraction. However, under conditions of small elapsed time and large density ratio, the transient mobility may exhibit an initial increase with particle volume fraction.
Full article
(This article belongs to the Special Issue 10th Anniversary of Fluids—Recent Advances in Fluid Mechanics)
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Open AccessArticle
Characterizing the Internal Flow Behavior of Spray Pulsating Operation in Internal-Mixing Y-Jet Atomizers
by
Matheus Rover Barbieri and Udo Fritsching
Fluids 2026, 11(1), 12; https://doi.org/10.3390/fluids11010012 - 30 Dec 2025
Abstract
The production of a stable and uniform spray is a primary concern in fuel atomization applications, such as in fluid catalytic cracking reactors, directly affecting the process quality and gas emissions. However, depending on nozzle geometry and operating conditions, undesired pulsed spray behavior
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The production of a stable and uniform spray is a primary concern in fuel atomization applications, such as in fluid catalytic cracking reactors, directly affecting the process quality and gas emissions. However, depending on nozzle geometry and operating conditions, undesired pulsed spray behavior may occur. This phenomenon originates from the internal multiphase flow interaction in Y-jet nozzles and leads to unstable sprays. Understanding the formation of spray pulsations is challenging due to limited internal flow visualization in the nozzle and the fast dynamics involved. Accordingly, this work elucidates the mechanisms of the pulsed spray formation through 3D transient numerical multiphase simulations inside a mixing chamber. The model is validated against internal pressure measurements and applied to investigate the internal mixing behavior across several operating conditions. Results show that the liquid-to-gas momentum flux ratio governs the internal flow regimes. A higher liquid momentum flux obstructs the gas flow, leading to periodic spray bursts when the gas overcomes the liquid back pressure. The simulations also reveal self-sustained oscillatory flow patterns and cyclic transitions between gas penetration and liquid accumulation, which produce periodic pressure fluctuations and nozzle discharge pulsations. The findings offer valuable guidance for optimizing nozzle operation and geometry to suppress pulsation and improve atomization performance.
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(This article belongs to the Special Issue Spray Dynamics and Cooling)
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Open AccessArticle
Analysis of Turbulence Models to Simulate Patient-Specific Vortex Flows in Aortic Coarctation
by
Nikita Skripka, Aleksandr Khairulin and Alex G. Kuchumov
Fluids 2026, 11(1), 11; https://doi.org/10.3390/fluids11010011 - 30 Dec 2025
Abstract
Coarctation of the aorta is a localized narrowing of the aortic lumen. This pathology leads to hypertension in upper extremity vessels, left ventricular hypertrophy and to impaired perfusion of the abdominal cavity and lower extremities. Along with traditional diagnostic methods, mathematical modeling is
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Coarctation of the aorta is a localized narrowing of the aortic lumen. This pathology leads to hypertension in upper extremity vessels, left ventricular hypertrophy and to impaired perfusion of the abdominal cavity and lower extremities. Along with traditional diagnostic methods, mathematical modeling is used for risk assessment and the prediction of disease outcomes. However, when applying numerical models to describe hemodynamic parameters, the choice of turbulence model to describe swirling flow occurring in the aorta in this pathology must be justified. Thus, three turbulence models, namely k-ε, k-ω, and SST were analyzed for the description of swirling flows in the study of coarctation’s effect on hemodynamic parameters and analysis of the mechanisms leading to various cardiovascular diseases caused by altered hemodynamics. The results revealed significant differences in swirling flow patterns between the k-ε and k-ω models, while the k-ω and SST models showed consistent results over the cardiac cycle. In the peak systolic phase, average velocity rises to 1.07–1.98 m·s−1 for the k-ε model, 0.82–2.12 m·s−1 for the k-ω model, 1.22–2.12 m·s−1 for the SST model and 0.8–2.12 m·s−1 for laminar flow. WSS values increase rapidly to 11–22 Pa in k-ε, 25–50 Pa in k-ω and SST models of turbulence, and 30–55 Pa for laminar flow. Significant differences were also evident in the prediction of wall shear stress, with the k-ε model giving values more than twice as high as the k-ω and SST models. The data obtained confirm the necessity of careful model selection for accurate hemodynamic parameter estimation, especially in coarctation. The findings of this study can be used for further physics-informed neural network analysis of evaluation of treatment evaluations for congenital heart disease patients.
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(This article belongs to the Special Issue Biological Fluid Dynamics, 2nd Edition)
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Open AccessArticle
Pressure Field Estimation from 2D-PIV Measurements: A Case Study of Fish Suction-Feeding
by
Jensine C. Coggin, Duval Dickerson-Evans, Erin E. Hackett and Roi Gurka
Fluids 2026, 11(1), 10; https://doi.org/10.3390/fluids11010010 - 29 Dec 2025
Abstract
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Particle image velocimetry (PIV) flow measurements are common practice in laboratory settings in a wide variety of fields involving fluid dynamics, including biology, physics, engineering, and medicine. Dynamic fluid pressure is a notoriously difficult property to measure non-intrusively, yet its variation is a
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Particle image velocimetry (PIV) flow measurements are common practice in laboratory settings in a wide variety of fields involving fluid dynamics, including biology, physics, engineering, and medicine. Dynamic fluid pressure is a notoriously difficult property to measure non-intrusively, yet its variation is a driving flow force and critical to model correctly. Techniques have been developed to estimate the pressure from velocity and velocity gradient measurements. Here, we highlight a novel application of boundary conditions when applying such pressure estimation techniques based on two-dimensional PIV data; the novel method is especially relevant to problems with complex boundary conditions. As such, it is demonstrated with PIV measurements of in vivo fish suction-feeding, which represents a challenging flow environment. Suction-feeding is a common method for capturing prey by aquatic organisms. Suction-feeding is a complex fish–fluid interaction governed by various hydrodynamic forces and the dynamic behavior of the fish (motion and forces). This study focuses on estimating the pressure within the flow field surrounding the mouth of a Bluegill sunfish (Lepomis macrochirus) during suction-feeding utilizing two-dimensional PIV measurements. High-speed imaging was used for measurements of the fish kinematics (duration and amplitude). Through the Poisson equation, the pressure field is estimated from the PIV velocity measurements. The boundary conditions for the pressure field are determined from the integral momentum equation, separately for three phases of the suction-feeding cycle. We demonstrate the utility of the technique with this case study on fish suction-feeding by quantifying the pressure field that drives the flow towards the buccal cavity, a feeding mechanism known to be dominated by pressure spatial variations over the feeding cycle.
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Open AccessArticle
Performance Analysis of a Novel 3D-Printed Three-Blade Savonius Wind Turbine Rotor with Pointed Deflectors
by
Edward Ang and Jaime Honra
Fluids 2026, 11(1), 9; https://doi.org/10.3390/fluids11010009 - 29 Dec 2025
Abstract
This study presents a compact, 3D-printed Savonius wind turbine rotor incorporating pointed deflectors to enhance concave-side airflow and mitigate blade-edge vortex formation. The prototype, fabricated from ABS plastic, was experimentally evaluated in an Eiffel-type wind tunnel under low-speed wind conditions (3, 4, and
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This study presents a compact, 3D-printed Savonius wind turbine rotor incorporating pointed deflectors to enhance concave-side airflow and mitigate blade-edge vortex formation. The prototype, fabricated from ABS plastic, was experimentally evaluated in an Eiffel-type wind tunnel under low-speed wind conditions (3, 4, and 5 m/s), with blockage effects taken into account. Flow visualization revealed improved airflow attachment and pressure concentration on the concave blade surfaces, increasing drag asymmetry and torque generation. Corresponding power coefficients with applied blockage ratio were observed to be 0.181, 0.185 and 0.186, while torque coefficients with applied blockage ratio were observed to be 0.385, 0.374 and 0.375 at each wind speed and optimal tip-speed ratio, respectively, and were compared with previously reported computational results. The optimal operating tip-speed ratios identified for the torque and power coefficients were remarkably close, enabling efficient torque and power generation during operation. The experimental findings validate earlier numerical predictions and underscore the importance of physical testing in assessing turbine performance. Observed deviations between predicted and experimental coefficients suggest that fabrication parameters may influence prototype performance and warrant further investigation. Overall, the results demonstrate the technical viability of 3D-printed Savonius turbines for small-scale urban energy harvesting applications in the Philippines.
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(This article belongs to the Section Mathematical and Computational Fluid Mechanics)
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Open AccessArticle
Nonlinear Temperature and Pumped Liquid Dependence in Electromagnetic Diaphragm Pump
by
Grazia Lo Sciuto, Rafał Brociek, Szymon Skupień, Paweł Kowol, Salvo Coco and Giacomo Capizzi
Fluids 2026, 11(1), 8; https://doi.org/10.3390/fluids11010008 - 28 Dec 2025
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Electromagnetic pumps are developed for industrial, medical and scientific applications, moving electrically conductive liquids and molten solder in electronics manufacturing using electromagnetism instead of mechanical parts. This study presents a comprehensive thermal analysis of an electromagnetic diaphragm pump, focusing on the influence of
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Electromagnetic pumps are developed for industrial, medical and scientific applications, moving electrically conductive liquids and molten solder in electronics manufacturing using electromagnetism instead of mechanical parts. This study presents a comprehensive thermal analysis of an electromagnetic diaphragm pump, focusing on the influence of operating current, permanent magnet switching speed, and cooling conditions on pumping performance. The pump utilizes a flexible diaphragm embedded with a permanent neodymium magnet, which interacts with time-varying magnetic fields generated by electromagnets to drive fluid motion. Temperature monitoring is conducted using a waterproof DS18B20 sensor and an uncooled FLIR A325sc infrared camera, allowing accurate mapping of thermal distribution across the pump surface. Experimental results demonstrate that higher current and increased magnet switching speed lead to faster temperature rise, impacting the volume of fluid pumped. Incorporation of an automatic cooling fan effectively reduces coil temperature and stabilizes pump performance. Polynomial regression models describe the relationship between temperature, pumped liquid volume, and magnet switching speed, providing information to optimize pump operation and cooling strategies. The novel relationship between temperature and the volume of the pumped liquid is considered as a fourth-degree polynomial. In particular the model describes a quantitative evaluation of the effect of heating on pumping efficiency. An initial increase in temperature correlates with a higher pumped volume, but excessive heating leads to efficiency saturation or even decline. Indeed, mathematical dependencies are crucial in mechanical pump engineering for analyzing physical phenomena; this is achieved by using a mathematical equation to define how different physical variables are related to each other, enabling engineers to calculate performance and optimize the pump design.
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