Fluids

21 pages, 5290 KB

Open AccessArticle

Unsteady Modelling of the Mixing Efficiency, Species Transport, and Flow Structure in a Novel Photochemical Reactor

by Zakaria Mansouri, Richard Jefferson-Loveday, Stephen J. Pickering and Michael W. George

Fluids 2026, 11(2), 45; https://doi.org/10.3390/fluids11020045 - 5 Feb 2026

This paper deals with computational fluid dynamics (CFD) to improve the design of a new scalable photochemical reactor which uses the Taylor–Couette flow principle. This study aims to investigate the ways to improve the mixing efficiency (M_eff) within the reactor, as [...] Read more.

This paper deals with computational fluid dynamics (CFD) to improve the design of a new scalable photochemical reactor which uses the Taylor–Couette flow principle. This study aims to investigate the ways to improve the mixing efficiency (M_eff) within the reactor, as it is a key parameter to increase the productivity and inform the future scale-up of the novel reactor. The investigated design parameters are the gap size (d) between the reactor cylinders, the rotational speed (Ω) of the inner cylinder, the flow rate of the reagent (

\dot{V}

), and the dynamic viscosity of the mixture (μ). For all the investigated cases, the results show that the temporal evolution of the M_eff increases and then becomes steady after a maximum level is reached. The point of the maximum M_eff is called the equilibration time. It is revealed that the M_eff is mainly affected by the flow rate increase as it contracts the Taylor vortices and consequently the mixing deteriorates. Full article

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

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15 pages, 5071 KB

Open AccessArticle

Investigation of the Mass Transfer Ratio in a Bubble Column Operated with Various Organic Liquids and Mixtures Under Ambient Conditions

by Stoyan Nedeltchev

Fluids 2026, 11(2), 44; https://doi.org/10.3390/fluids11020044 - 4 Feb 2026

Abstract

In this work, for the first time, the dependence of the mass transfer (MT) ratio (k_La coefficient to overall gas holdup) as a function of the superficial gas velocity U_G in seven organic liquids was studied. The volumetric liquid-phase [...] Read more.

In this work, for the first time, the dependence of the mass transfer (MT) ratio (k_La coefficient to overall gas holdup) as a function of the superficial gas velocity U_G in seven organic liquids was studied. The volumetric liquid-phase MT coefficients k_La were recorded (by means of a polarographic oxygen electrode) in a bubble column (0.095 m in ID) equipped with a single tube (∅3.0 mm in ID) as a gas sparger. It was found that the MT ratio decreases monotonically through all main flow regimes. Both the constant and the exponent of the empirical correlation between the MT ratio and U_G were analyzed, and it was found that they depended in a complicated fashion on the Schmidt number, Sc. In three different regions of the Sc number, potential new correlations were discussed. The main conclusion from this work is that the MT ratio is not constant in the heterogeneous regime as reported previously by other researchers. In the case of four binary mixtures between benzene and cyclohexane, it was also found that the MT ratio decreased monotonically as a function of the superficial gas velocity, U_G. The effects of both liquid viscosity and surface tension on the MT ratio were also investigated. Full article

(This article belongs to the Special Issue Mass Transfer in Multiphase Reactors)

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35 pages, 10624 KB

Open AccessArticle

Advancing CFD Simulations Through Machine-Learning-Enabled Mesh Refinement Analysis

by Charles Patrick Bounds and Mesbah Uddin

Fluids 2026, 11(2), 43; https://doi.org/10.3390/fluids11020043 - 30 Jan 2026

Abstract

As computational fluid dynamics (CFD) has become more mainstream in production engineering workflows, new demands have been introduced that require high-quality meshes to accurately capture the complex geometries. This evolution has created the need for mesh generation frameworks that help engineers design optimized [...] Read more.

As computational fluid dynamics (CFD) has become more mainstream in production engineering workflows, new demands have been introduced that require high-quality meshes to accurately capture the complex geometries. This evolution has created the need for mesh generation frameworks that help engineers design optimized meshing structures for each new geometry. However, many simulation workflows rely on the experience and intuition of senior engineers rather than systematic frameworks. In this paper, a novel technique for determining mesh convergence is created using machine learning (ML). This method seeks to provide process engineers with a visual feedback mechanism of flow regions that require mesh refinement. The work was accomplished by creating three grid sensitivity studies on various geometries: zero-pressure-gradient flat plate, bump in channel, and axisymmetric free jet. The cases were then simulated using the Reynolds Averaged Navier-Stokes (RANS) models in OpenFOAM (v2306) and had the ML method applied post-hoc using Python (v3.12.6). To apply the method to each case, the flow field was regionalized and clustered using an unsupervised ML model. The ML clustering results were then converted into a similarity score, which compares two grid levels to inform the user whether the region of the flow had converged. To prove this framework, the similarity scores were compared to flow field probes used to determine mesh convergence at key points in the flow. The method was found to be in agreement with the flow field probes on the level of mesh refinement that created convergence. The approach was also seen to provide refinement region recommendations in regions of the flow that align with human intuition of the physics of the flow. Full article

(This article belongs to the Special Issue Machine Learning and Artificial Intelligence in Fluid Mechanics, 2nd Edition)

25 pages, 8004 KB

Open AccessArticle

Effects of Discharge and Tailwater Depth on Local Scour of Multi-Grain Beds by Circular Wall Jets

by Amir H. Azimi and Homero Hernandez

Fluids 2026, 11(2), 42; https://doi.org/10.3390/fluids11020042 - 30 Jan 2026

Abstract

The scour process of sand particles and multi-grain size and density particles were studied to investigate the segregation process of different particles in a confined channel. The effects of jet intensity and submergence as two controlling parameters were studied, and scour characteristics and [...] Read more.

The scour process of sand particles and multi-grain size and density particles were studied to investigate the segregation process of different particles in a confined channel. The effects of jet intensity and submergence as two controlling parameters were studied, and scour characteristics and profiles were measured. The time history of the scouring process was measured and the results were compared with the scour process in a uniform sand bed as benchmark tests. Experimental data revealed that the eroded area of different particle types increased with the jet intensity, but the erosion of relatively heavier particles was limited due to jet diffusion. The local erosion was affected by the level of submergence and more erosion occurred near the nozzle at low submergence. Increasing the jet Froude number increased the area of deposition, while submergence reduced the overall area of deposition. As submergence increased from 4 to 12, the area of sand particles reduced by more than 50% while the jet intensity was constant. In shallow submergence, increasing jet intensity from 1.46 to 2.11 increased the area of lead balls by 120%, whereas in relatively deep submergence, incrementing jet intensity increased the area of lead balls by more than five times. The effect of flow intensity on variations of scour dimensions was quantified by the densimetric Froude number. While a densimetric Froude number based on mean particle size, D₅₀, was found to be suitable to estimate maximum scour bed in uniform sand beds, experimental data indicated that the best fit is achievable to predict maximum scour depth in multi-grain size and density once D₉₅ is used. Semi-empirical models were proposed to predict scour dimensions as a function of the densimetric Froude number. Full article

(This article belongs to the Topic Advances in Environmental Hydraulics, 2nd Edition)

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17 pages, 5075 KB

Open AccessArticle

Hydrodynamic Performance and Cavitation Characteristics of an Integrated Pump-Gate

by Yiming Li, Zhengwen Tang, Qiqing Chen, Deyang Liu, Jinxin Zou, David Yang, Xiangrong Luo and Yun Long

Fluids 2026, 11(2), 41; https://doi.org/10.3390/fluids11020041 - 30 Jan 2026

Abstract

The integrated pump-gate is a hydraulic facility that integrates a pumping station and a gate, playing a vital role in urban drainage systems, flood control, and other scenarios. Although integrated pump-gates are widely used, their internal flow presents different forms depending on the [...] Read more.

The integrated pump-gate is a hydraulic facility that integrates a pumping station and a gate, playing a vital role in urban drainage systems, flood control, and other scenarios. Although integrated pump-gates are widely used, their internal flow presents different forms depending on the application scenarios, such as backflow, vortices, and cavitation. These effects markedly influence the pump’s hydraulic performance, operational stability, and overall reliability. This study investigates the cavitation characteristics and internal flow fields within the complex geometry of the integrated pump-gate and numerically simulates the cavitation phenomenon using the SST turbulence model. Specifically, the influence of the impeller, guide vanes, and structural supports on the cavitation performance and internal flow state was analyzed. The results show that the geometric characteristics of the impeller’s leading edge significantly influence the cavitation structure. Regarding cavitation performance, NPSH_c was determined to be 5.3 m. At the leading edge of the guide vanes, cavitation usually occurs at the axial diffusion position of the flow channel, and the degree of cavitation is affected by the relative position of the guide vanes and the impeller blades. The structural supports and protrusions significantly affect the vortex structures in the flow field, with protrusion-induced vortex clusters dominating the guide vane region. Full article

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24 pages, 11871 KB

Open AccessArticle

MCV-Driven Effective Viscosity Modulation and Its Hemodynamic Impact in an Idealized Carotid Bifurcation: A Computational Fluid Dynamics Study

by Arif Çutay, Hakan Bayrakcı, Özdeş Çermik and Muharrem İmal

Fluids 2026, 11(2), 40; https://doi.org/10.3390/fluids11020040 - 29 Jan 2026

Abstract

Mean corpuscular volume (

M C V

) is a routinely measured hematological parameter that influences blood viscosity by altering red blood cell volume and packing density. Although

M C V

is physiologically linked to hemorheological behavior, to the authors’ knowledge, its direct [...] Read more.

Mean corpuscular volume (

M C V

) is a routinely measured hematological parameter that influences blood viscosity by altering red blood cell volume and packing density. Although

M C V

is physiologically linked to hemorheological behavior, to the authors’ knowledge, its direct role in modulating large-artery hemodynamics has not been systematically quantified. This study introduces an

M C V

-driven effective Newtonian viscosity mode to evaluate the first-order impact of

M C V

variation on carotid bifurcation flow. Rather than employing shear-dependent constitutive laws, blood viscosity was scaled through an

M C V

-based formulation, yielding three Newtonian fluids corresponding to clinically relevant

M C V

levels of 70, 90, and 110 fL. Pulsatile CFD simulations were performed in four idealized carotid bifurcation geometries (40°, 50°, 65°, and 100°) to assess the combined influence of vascular geometry and

M C V

-dependent viscosity variation. Hemodynamic indices including time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), and relative residence time (RRT) were quantified, and a two-way analysis of variance (ANOVA) was employed to distinguish the relative contributions of geometric configuration and

M C V

. Across the investigated

M C V

range, increasing

M C V

produced a geometry-dependent modulation of shear-based indices, with TAWSS increasing by up to approximately 11%, while OSI and RRT decreased by about 20–25% and 10%, respectively, particularly in geometries exhibiting pronounced flow separation. Although vascular geometry remained the dominant determinant of overall hemodynamic patterns,

M C V

-induced viscosity scaling significantly modulated low-shear and recirculation regions. These findings suggest that

M C V

-dependent viscosity scaling can complement patient-specific hemodynamic assessments and provide a rational baseline for future shear-dependent and personalized rheological modeling frameworks. Full article

(This article belongs to the Special Issue Advances in Computational Mechanics of Non-Newtonian Fluids, 2nd Edition)

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29 pages, 24358 KB

Open AccessArticle

Study on Fluid–Structure Interaction Characteristics of Reed Valves in a Reciprocating Refrigeration Compressor

by Ying Zhao, Tao Wang, He Xu, Qixiang Zheng and Fengyu Fan

Fluids 2026, 11(2), 39; https://doi.org/10.3390/fluids11020039 - 29 Jan 2026

Abstract

The suction and discharge reed valves are critical components of reciprocating refrigeration compressors, as their dynamic behavior strongly affects the compressor performance. This study investigates the interaction mechanism between unsteady flow characteristics and valve dynamics in a reciprocating refrigeration compressor. A 3D fluid–structure [...] Read more.

The suction and discharge reed valves are critical components of reciprocating refrigeration compressors, as their dynamic behavior strongly affects the compressor performance. This study investigates the interaction mechanism between unsteady flow characteristics and valve dynamics in a reciprocating refrigeration compressor. A 3D fluid–structure interaction (FSI) simulation model was developed, and its reliability was validated by comparing the simulated in-cylinder pressure and suction valve lift with the corresponding experimental measurements. The validated model was subsequently utilized to analyze the evolution of unsteady flow characteristics and valve deformations. Furthermore, a series of FSI simulations was performed to examine the influence of suction pressure, rotational speed, clearance volume ratio, suction valve plate thickness, and discharge valve plate thickness on valve dynamics and compressor performance. The results indicated that suction pressure, rotational speed, and clearance volume ratio all exerted a significant influence on the dynamics of both the suction and discharge valves. Variations in suction valve plate thickness exhibited a minor influence on the dynamic behavior and flow resistance of the discharge valve, whereas adjustments to discharge valve plate thickness had almost no impact on those of the suction valve. This weak coupling characteristic provides flexibility for the independent optimization of the suction and discharge reed valves. The findings of this study lay a solid foundation for optimizing valve design and improving compressor performance. Full article

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

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11 pages, 5975 KB

Open AccessArticle

Rheological Characterization of Cerebrospinal Fluid Under Different Temperature Conditions

by Thessa-Carina Bauer, Elke Bradt, Sabine Hild, Andreas Gruber, Tobias Rossmann, Francisco Ruiz-Navarro, Johannes Oberndorfer, Harald Stefanits and Milan Kracalik

Fluids 2026, 11(2), 38; https://doi.org/10.3390/fluids11020038 - 28 Jan 2026

Abstract

The flow behavior of fluids can be characterized by rheology and is especially used in the field of polymeric materials. This study focused on characterizing cerebrospinal fluid (CSF) of patients who developed hydrocephalus after subarachnoid hemorrhage (SAH) with rheology. Samples were drawn from [...] Read more.

The flow behavior of fluids can be characterized by rheology and is especially used in the field of polymeric materials. This study focused on characterizing cerebrospinal fluid (CSF) of patients who developed hydrocephalus after subarachnoid hemorrhage (SAH) with rheology. Samples were drawn from an external ventricular drainage (EVD) at four pre-defined time points after the initial hemorrhage. The CSF samples were analyzed using a rotational rheometer with a double gap geometry. In addition to the characterization of viscoelastic parameters, the cumulative storage factor was calculated to determine the interactions in the fluid. In order to investigate the temperature dependence of the CSF properties, the oscillatory measurements were implemented at certain temperatures that simulated specific conditions, such as 5 °C, at which temperature the CSF samples were stored; 35 °C for hypothermic conditions; 37 °C for physiologic conditions; and 40 °C for elevated body temperature. The overall goal was to evaluate whether rheology-based parameters may help in the prediction of shunt dependence for post-hemorrhagic hydrocephalus patients. For this aim, rheological parameters were correlated to certain laboratory parameters, such as erythrocyte and leukocyte count, glucose, lactate, and total protein concentration. Full article

(This article belongs to the Section Non-Newtonian and Complex Fluids)

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8 pages, 188 KB

Open AccessEditorial

Advances in Pipe and Channel Flow Modeling

by Kamil Urbanowicz

Fluids 2026, 11(2), 37; https://doi.org/10.3390/fluids11020037 - 28 Jan 2026

Abstract

The fluid flow within confined conduits (pipes and channels) remains a cornerstone of hydraulic engineering, underpinning the design, analysis and safe operation of countless industrial, environmental and infrastructural systems [...] Full article

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

19 pages, 6272 KB

Open AccessArticle

Numerical Study on the Aerodynamic Performance and Noise of Composite Bionic Airfoils

by Shunlong Su, Shenwei Xin, Xuemin Ye and Chunxi Li

Fluids 2026, 11(2), 36; https://doi.org/10.3390/fluids11020036 - 28 Jan 2026

Abstract

Bionic airfoils are an effective method to improve aerodynamic performance and reduce the noise of wind turbine blades. To explore the impact of the lower surface of bird wing airfoils on the aerodynamic performance and noise of blades, this study combines the upper [...] Read more.

Bionic airfoils are an effective method to improve aerodynamic performance and reduce the noise of wind turbine blades. To explore the impact of the lower surface of bird wing airfoils on the aerodynamic performance and noise of blades, this study combines the upper surface of the NACA0018 airfoil with the lower surfaces of the teal, long-eared owl, and sparrowhawk (CBA-T, CBA-O, CBA-S) to create three new composite bionic airfoils (CBAs). The aerodynamic performance of these airfoils is evaluated, and the CBA-O airfoil is identified as having the best aerodynamic characteristics. A comparison of the noise and vortex structures of the CBA-O, owl wing airfoil, and NACA0018 is conducted, and the mechanisms behind the CBA-O airfoil performance improvement and noise reduction are explored. The results indicate that the CBAs enhance the aerodynamic performance of the airfoils. Before stall, the aerodynamic performance of the CBA-O improves the lift-to-drag ratio by 12.7% and 119.7% compared to the owl and NACA0018 airfoils, with its average SPL significantly lower than that of the NACA0018. The CBA-O has smaller vortex sizes at the trailing-edge, and the wake vortex develops more stably, effectively reducing both surface radiation noise and wake noise. Full article

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

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24 pages, 5259 KB

Open AccessArticle

Design Methodology and Experimental Verification of a Novel Orifice Plate Rectifier

by Zhe Li, Guixiang Lu, Yan Li, Yanhua Lai, Zhen Dong and Mingxin Lyu

Fluids 2026, 11(2), 35; https://doi.org/10.3390/fluids11020035 - 28 Jan 2026

Abstract

Optimizing the rectification and pressure loss controlled by the aperture structure is challenging, with particular attention paid to the problem of precisely modeling the rectification process of multilayer wire mesh in pulse tube cryocoolers. This work offers a rectifier design method based on [...] Read more.

Optimizing the rectification and pressure loss controlled by the aperture structure is challenging, with particular attention paid to the problem of precisely modeling the rectification process of multilayer wire mesh in pulse tube cryocoolers. This work offers a rectifier design method based on the regularized orifice plate. A novel rectifier that reduces flow resistance and shows rectification performance comparable to a woven wire mesh is created by analyzing its effects on the flow using numerical simulation. Flow uniformity and pressure loss are selected as evaluation metrics. Point flow velocity calibration is performed under fully developed flow conditions to derive a quantitative equation relating voltage to flow velocity. A multi-cross-section radial flow velocity distribution test platform is set up. The experimental results show that the uniformity of woven wire mesh reaches 0.9670 under low-flow conditions and 0.9629 for the novel eight-ring rectifier, but the pressure drop reduction reaches 57.64%; the uniformity of the novel eight-ring rectifier is improved by 0.91~1.94% compared to that of woven wire mesh under high-flow conditions, and the pressure drop is reduced by 87.74~89.09%. The rectifier features uniformly distributed apertures, facilitating modeling and machining. Full article

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

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24 pages, 5943 KB

Open AccessArticle

A Fully Implicit Model of Compressible Capillary Flows

by Jean-Paul Caltagirone

Fluids 2026, 11(2), 34; https://doi.org/10.3390/fluids11020034 - 27 Jan 2026

Abstract

Small-scale two-phase flows are subject to intense capillary accelerations that must be treated with care in order to avoid artifacts often associated with the numerical methodologies used, such as excessive fragmentation of structures. This analysis proposes a formulation of capillary actions for compressible [...] Read more.

Small-scale two-phase flows are subject to intense capillary accelerations that must be treated with care in order to avoid artifacts often associated with the numerical methodologies used, such as excessive fragmentation of structures. This analysis proposes a formulation of capillary actions for compressible viscous two-phase flows within the framework of discrete mechanics, where the concept of mass is abandoned in favor of a law of motion that describes the conservation of accelerations, one related to inertia and the other to external actions. With the introduction of the capillary term, the sum of a capillary potential gradient and the dual curl of a vector potential is consistent with the other terms of the law of motion, a formal Helmholtz–Hodge decomposition. This fully compressible formulation reproduces the capillary waves generated by the source terms and the contact and shock discontinuities in the two immiscible fluids. This methodology completely eliminates parasitic currents due mainly to the presence of residual curl in the capillary source terms. Several classic examples demonstrate the validity of this approach. Full article

(This article belongs to the Special Issue Multiphase Simulations with the Volume-of-Fluid (VOF) Approach)

21 pages, 4251 KB

Open AccessArticle

Comparative Analysis of Unsteady Natural Convection and Thermal Performance in Rectangular and Square Cavities Filled with Stratified Air

by Syed Mehedi Hassan Shaon, Md. Mahafujur Rahaman, Suvash C. Saha and Sidhartha Bhowmick

Fluids 2026, 11(2), 33; https://doi.org/10.3390/fluids11020033 - 27 Jan 2026

Abstract

A comprehensive numerical analysis has been conducted to investigate unsteady natural convection (UNC), bifurcation behavior, and heat transfer (HT) in a rectangular enclosure containing thermally stratified air. The enclosure comprises a uniformly heated bottom wall, thermally stratified vertical sidewalls, and a cooled top [...] Read more.

A comprehensive numerical analysis has been conducted to investigate unsteady natural convection (UNC), bifurcation behavior, and heat transfer (HT) in a rectangular enclosure containing thermally stratified air. The enclosure comprises a uniformly heated bottom wall, thermally stratified vertical sidewalls, and a cooled top wall. To assess thermal performance, square and rectangular cavities with identical boundary conditions and working fluid are considered. The finite volume method (FVM) is used to solve the governing equations over a wide range of Rayleigh numbers (Ra = 10¹ to 10⁹) for air with a Prandtl number (Pr) of 0.71. Flow dynamics and thermal performance are analyzed using temperature time series (TTS), limit point–limit cycle behavior, average Nusselt number (Nu_avg), average entropy generation (S_avg), average Bejan number (Be_avg), and the ecological coefficient of performance (ECOP). In the rectangular cavity, the transition from steady to chaotic flow exhibits three bifurcations: a pitchfork bifurcation at Ra = 3 × 10⁴–4 × 10⁴, a Hopf bifurcation at Ra = 3 × 10⁶–4 × 10⁶, and the onset of chaotic flow at Ra = 9 × 10⁷–2 × 10⁸. The comparative analysis indicates that Nu_avg remains nearly identical for both cavities within Ra = 10⁵ to 10⁷. However, at Ra = 10⁸, the HT rate in the rectangular cavity is 29.84% higher than that of the square cavity, while S_avg and Be_avg differ by 39.32% and 37.50%, respectively. Despite higher HT and S_avg in the rectangular enclosure, the square cavity demonstrates superior overall thermal performance by 13.52% at Ra = 10⁸. These results offer significant insights for optimizing cavity geometries in thermal system design based on energy efficiency and entropy considerations. Full article

(This article belongs to the Special Issue Convective Flows and Heat Transfer)

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3 pages, 143 KB

Open AccessEditorial

Editorial: Rarefied Gas Flows—From Micro–Nano Scale to the Hypersonic Regime

by Ehsan Roohi

Fluids 2026, 11(2), 32; https://doi.org/10.3390/fluids11020032 - 26 Jan 2026

Abstract

Rarefied gas dynamics spans a wide spectrum of applications: micro–nano devices where the mean free path becomes comparable to characteristic lengths, vacuum and porous systems where Knudsen diffusion emerges, and high-speed (including hypersonic) flows where non-equilibrium effects shape transport and surface interactions [...] [...] Read more.

Rarefied gas dynamics spans a wide spectrum of applications: micro–nano devices where the mean free path becomes comparable to characteristic lengths, vacuum and porous systems where Knudsen diffusion emerges, and high-speed (including hypersonic) flows where non-equilibrium effects shape transport and surface interactions [...] Full article

(This article belongs to the Special Issue Rarefied Gas Flows: From Micro-Nano Scale to Hypersonic Regime)

17 pages, 10638 KB

Open AccessArticle

Numerical Investigation of Noise Generation from a Variable-Pitch Propeller at Various Flight Conditions

by Mateus Grassano Lattari, Victor Henrique Pereira da Rosa, Filipe Dutra da Silva and César José Deschamps

Fluids 2026, 11(2), 31; https://doi.org/10.3390/fluids11020031 - 26 Jan 2026

Abstract

The advent of electric propulsion for new aircraft designs necessitates the optimization of propeller aerodynamic performance and the reduction of acoustic signatures. Variable-pitch propellers present a promising solution, offering the flexibility to adjust blade angles in response to different flight conditions. The study [...] Read more.

The advent of electric propulsion for new aircraft designs necessitates the optimization of propeller aerodynamic performance and the reduction of acoustic signatures. Variable-pitch propellers present a promising solution, offering the flexibility to adjust blade angles in response to different flight conditions. The study investigates the performance of blade pitch configurations tailored to specific flight conditions. Rather than a dynamic pitch change, the research evaluates discrete pitch settings coupled with corresponding advance ratios to identify optimal operating points. Findings show that increasing collective pitch in response to a higher advance ratio (forward flight) successfully maintains aerodynamic efficiency and thrust, with an expected increase in torque. While this adjustment leads to an anticipated rise in noise due to higher aerodynamic loading, results reveal that a collective pitch increment of

+ 5 °

actively suppresses broadband noise at frequencies above 2 kHz. Analysis of the flow field and surface pressure fluctuations indicates this suppression is directly attributed to the mitigation of outboard propeller stall. Ultimately, this work demonstrates the feasibility of using collective pitch adjustments not only to enhance flight performance but also to actively control and suppress components of the propeller noise signature, such as the broadband noise. Full article

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

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16 pages, 1117 KB

Open AccessArticle

Algebraic Prediction of Pressure and Lift for High-Angle-of-Attack Supersonic Asymmetric Delta Wings Based on Geometric Similarity

by Xue-Ying Wang, Jie Peng and Zi-Niu Wu

Fluids 2026, 11(2), 30; https://doi.org/10.3390/fluids11020030 - 24 Jan 2026

Abstract

In this paper, we explore the feasibility of deriving a simple, physically meaningful, and compact formulation for the pressure distribution and lift of an asymmetric delta wing at high angles of attack with an attached shock wave. Such a model would be valuable [...] Read more.

In this paper, we explore the feasibility of deriving a simple, physically meaningful, and compact formulation for the pressure distribution and lift of an asymmetric delta wing at high angles of attack with an attached shock wave. Such a model would be valuable for rapid engineering analysis. Our approach begins with a compact pressure approximation in the linear regime, which is then extended to the nonlinear case through a geometric transformation and the assumption of functional similarity between linear and nonlinear solutions. This method bridges the solution in the central nonuniform flow region to the exact solutions in the uniform flow regions near the leading-edge shock waves, in a manner analogous to methods used for supersonic starting flow. The model is shown to reproduce existing results for both symmetric and yawed delta wings within an acceptable error margin, providing a compact explicit expression for the normal force coefficient as a weighted average of pressure coefficients from the two uniform flow regions. Additionally, we outline how the approach may be extended to the upper surface, where the uniform flow is described by swept Prandtl–Meyer relations. Full article

(This article belongs to the Special Issue High-Speed Processes in Continuous Media)

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27 pages, 3203 KB

Open AccessArticle

Machine Learning and Physics-Informed Neural Networks for Thermal Behavior Prediction in Porous TPMS Metals

by Mohammed Yahya and Mohamad Ziad Saghir

Fluids 2026, 11(2), 29; https://doi.org/10.3390/fluids11020029 - 23 Jan 2026

Abstract

Triply periodic minimal surface (TPMS) structures provide high surface area to volume ratios and tunable conduction pathways, but predicting their thermal behavior across different metallic materials remains challenging because multi-material experimentation is costly and full-scale simulations require extremely fine meshes to resolve the [...] Read more.

Triply periodic minimal surface (TPMS) structures provide high surface area to volume ratios and tunable conduction pathways, but predicting their thermal behavior across different metallic materials remains challenging because multi-material experimentation is costly and full-scale simulations require extremely fine meshes to resolve the complex geometry. This study develops a physics-informed neural network (PINN) that reconstructs steady-state temperature fields in TPMS Gyroid structures using only two experimentally measured materials, Aluminum and Silver, which were tested under identical heat flux and flow conditions. The model incorporates conductivity ratio physics, Fourier-based thermal scaling, and complete spatial temperature profiles directly into the learning process to maintain physical consistency. Validation using the complete Aluminum and Silver datasets confirms excellent agreement for Aluminum and strong accuracy for Silver despite its larger temperature gradients. Once trained, the PINN can generalize the learned behavior to nine additional metals using only their conductivity ratios, without requiring new experiments or numerical simulations. A detailed heat transfer analysis is also performed for Magnesium, a lightweight material that is increasingly considered for thermal management applications. Since no published TPMS measurements for Magnesium currently exist, the predicted Nusselt numbers obtained from the PINN-generated temperature fields represent the first model-based evaluation of its convective performance. The results demonstrate that the proposed PINN provides an efficient, accurate, and scalable surrogate model for predicting thermal behavior across multiple metallic TPMS structures and supports the design and selection of materials for advanced porous heat technologies. Full article

(This article belongs to the Special Issue Machine Learning and Artificial Intelligence in Fluid Mechanics, 2nd Edition)

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19 pages, 6334 KB

Open AccessArticle

Supercavitating Bubble Dynamics near Free Surfaces and Solid Walls

by Ping Wei, Mingdeng Weng, Xiaobin Yang, Yiding Hu, Weige Liang and Shiyan Sun

Fluids 2026, 11(1), 28; https://doi.org/10.3390/fluids11010028 - 21 Jan 2026

Abstract

This study investigates the hydrodynamic characteristics of supercavitating flows near boundaries through numerical simulations, focusing on the influence of free surfaces and solid walls. A validated numerical framework combining the Realizable k-ε turbulence model with the VOF multiphase approach and Schnerr–Sauer cavitation model [...] Read more.

This study investigates the hydrodynamic characteristics of supercavitating flows near boundaries through numerical simulations, focusing on the influence of free surfaces and solid walls. A validated numerical framework combining the Realizable k-ε turbulence model with the VOF multiphase approach and Schnerr–Sauer cavitation model is employed to capture complex phase interfaces and turbulent cavitating flows. Systematic validation against existing experimental data and dedicated underwater launch tests confirms the reliability of the methodology. The results demonstrate significant boundary effects on supercavitation dynamics. Near a free surface, the cavity tail deflects away from the interface, whereas it bends toward the wall when in close proximity to a solid boundary. Simultaneous presence of both boundaries causes combined torsional deformation and deflection. The cavity interface exhibits progressive indentation toward the tail, with indentation angle following a power–law relationship to axial position. Boundary interactions create distinct effects: free surfaces suppress cavity elongation, whereas solid walls promote extension, with cavity length remaining bounded within predictable limits. A notable torque reversal phenomenon occurs at

x = D

from the cavitator tip, creating positive torque upstream (x < D) and negative torque downstream (x > D). Full article

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

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16 pages, 4488 KB

Open AccessArticle

Reverse Steady Streaming Induced by a Freely Moving Wavy Wall

by José Carlos Domínguez-Lozoya, Sebastián Gutiérrez-Juárez, David Roberto Domínguez-Lozoya, Aldo Figueroa and Sergio Cuevas

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 [...] Read more.

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. Full article

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

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