European Journal of Mechanics B-fluids最新文献

{"title":"Lagrangian tracking of the wake vortices shedding from a wobbling bubble","authors":"Xinwei Ye ,&nbsp;Xiaojing Niu","doi":"10.1016/j.euromechflu.2025.204380","DOIUrl":"10.1016/j.euromechflu.2025.204380","url":null,"abstract":"<div><div>This study aims to elucidate the motion and the evolution of shedding vortices in the wake of a wobbling bubble based on experimental observation. Experimental observations of bubble wakes were conducted using Particle Image Velocimetry (PIV) for the ambient continuous phase and the backlight shadow imaging technique for the bubble. Vortices are detected and tracked in a Lagrangian framework based on the flow field in the vertical section. To investigate the three-dimensional structure of the flow field and to supplement the experimentally measured bubble sizes, bubbles with a diameter of 3–5 mm are numerically simulated, incorporating adaptive dynamic mesh refinement based on the bubble wake location. The study establishes a correlation between the transport velocity and swirling strength of wake vortices generated by wobbling bubbles and the bubble's parameters, facilitating more convenient predictions of wake behavior. The results indicate that the vortices trail the bubble at a transport velocity that is approximately 30 % of the bubbles’ velocity. During the vortex shedding process, the swirling strength of these vortices intensifies within a distance of 1.58 times the bubble radius and then decays with increasing distance from the bubble, following the formula of <span><math><mrow><mn>1</mn><mo>−</mo><mi>exp</mi><mrow><mo>(</mo><mrow><mo>−</mo><mn>1.75</mn><mo>/</mo><mi>x</mi></mrow><mo>)</mo></mrow></mrow></math></span>.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"115 ","pages":"Article 204380"},"PeriodicalIF":2.5,"publicationDate":"2025-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145217837","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Lseq2seq: A new reduced-order model for unsteady aerodynamic force identification","authors":"Yihua Pan ,&nbsp;Xiaomin An ,&nbsp;Yuqi Lei ,&nbsp;Xin Gao ,&nbsp;Chen Ji","doi":"10.1016/j.euromechflu.2025.204377","DOIUrl":"10.1016/j.euromechflu.2025.204377","url":null,"abstract":"<div><div>Identifying unsteady aerodynamic forces is a crucial and challenging task in aerodynamics. It is also a critical research foundation for other subjects such as aeroelasticity, aircraft design, and flight dynamics. The two mainstream methods used to identify unsteady aerodynamic forces are Computational Fluid Dynamics (CFD) and experiments. However, these methods have their limitations, such as lengthy computational expense and high resource consumption. This article proposes a new reduced-order model called Long Sequence to Sequence (Lseq2seq) based on deep sequence generation models to predict unsteady aerodynamic forces in an efficient way. The Lseq2seq model is then applied to determine the hysteresis loop for the NACA0012 airfoil and the unsteady aerodynamic force of the two-freedom oscillation of the NACA64A010 airfoil in transonic flow. The results are compared with other prevalent time-sequential networks, such as Sequence to Sequence (Seq2seq) and Gated Recurrent Unit (GRU). The proposed Lseq2seq model presents better precision and generalization ability for identification. Additionally, this article explores a combined predictor–corrector method called GRU-Lseq2seq to predict the flutter response of the NACA64A010 airfoil, and the results demonstrate that the combined model could achieve better prediction accuracy than the GRU model and could be used in flutter boundary prediction.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"115 ","pages":"Article 204377"},"PeriodicalIF":2.5,"publicationDate":"2025-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145155625","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Stability of hydromagnetic Couette flow in an anisotropic porous medium with oblique principal axes and constant wall transpiration","authors":"Cédric Gervais Njingang Ketchate ,&nbsp;Alain Dika ,&nbsp;Pascalin Tiam Kapen ,&nbsp;Didier Fokwa","doi":"10.1016/j.euromechflu.2025.204376","DOIUrl":"10.1016/j.euromechflu.2025.204376","url":null,"abstract":"<div><div>Understanding and controlling transitions in wall-bounded flows through porous substrates are essential for designing and improving engineering systems. This study examines the linear stability of electrically conducting plane Couette flow within a Brinkman porous layer that is mechanically anisotropic and bounded by permeable walls with uniform cross-flow (injection at the lower wall, suction at the upper wall) under an applied magnetic field. A normal-mode linearisation leads to a modified Orr-Sommerfeld eigenvalue problem, which is solved using Chebyshev spectral collocation to identify neutral curves and growth-rate patterns as variables such as the Darcy number, Hartmann number, mechanical anisotropy, perturbation wavenumber, phase angle, cross-flow Reynolds number, and the orientation of the principal permeability axis are varied. Results show that increasing the Darcy number and Hartmann number stabilizes the flow, while a higher perturbation wavenumber reduces amplification, meaning disturbances grow most at longer wavelengths. Mechanical anisotropy consistently destabilizes the flow, increasing peak growth rates, whereas changes in the orientation angle have little effect. The phase angle has a slight influence on stability at low wavenumbers but tends to stabilize the flow at higher wavenumbers. Meanwhile, the cross-flow Reynolds number causes only minor shifts in the neutral curves. These findings suggest practical methods for flow control in anisotropic porous magnetohydrodynamic systems, highlighting the stabilizing effects of magnetic damping and porous-matrix diffusion, as well as the destabilizing impact of strong anisotropy.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"115 ","pages":"Article 204376"},"PeriodicalIF":2.5,"publicationDate":"2025-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145217836","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Numerical investigation of two plane parallel turbulent buoyant jets: Effects of jet spacing and Richardson number on flow interaction and thermal transport","authors":"Sameer Kumar Sanu,&nbsp;Tanmoy Mondal","doi":"10.1016/j.euromechflu.2025.204373","DOIUrl":"10.1016/j.euromechflu.2025.204373","url":null,"abstract":"<div><div>This study presents a numerical investigation of two plane parallel turbulent buoyant jets (TPBJ) to examine the combined effects of jet spacing and buoyancy on flow interaction and thermal transport. Steady-state simulations are conducted by solving the Reynolds-averaged Navier–Stokes equations using the standard <span><math><mrow><mi>k</mi><mo>−</mo><mi>ϵ</mi></mrow></math></span> turbulence model with the Boussinesq approximation. The analysis considers jet spacing ratios (<span><math><mrow><mi>s</mi><mo>/</mo><mi>d</mi><mo>=</mo><mn>3</mn></mrow></math></span> to 11), where <span><math><mi>s</mi></math></span> is the centre-to-centre jet spacing and <span><math><mi>d</mi></math></span> is the nozzle width, and Richardson numbers (<span><math><mrow><mi>R</mi><mi>i</mi><mo>=</mo><mn>0</mn></mrow></math></span> to 1/2) to represent varying buoyancy levels. Results indicate that narrower spacing enhances jet interaction, strengthens entrainment, and leads to earlier merging, while wider spacing delays interaction and weakens vertical momentum. Buoyancy significantly alters the flow structure by accelerating jet convergence, increasing centreline velocity, and confining both velocity and thermal plumes. Three characteristic axial locations, namely, the merging point (MP), combined point (CP), and maximum velocity point (MVP), are identified and correlated with <span><math><mrow><mi>s</mi><mo>/</mo><mi>d</mi></mrow></math></span> and <span><math><mrow><mi>R</mi><mi>i</mi></mrow></math></span>. In the far field, the lateral growth of velocity and thermal widths becomes approximately linear, though spreading rates decrease with increasing buoyancy. The centreline velocity and temperature exhibit decay consistent with power-law behaviour, influenced by buoyancy strength. Empirical correlations are proposed to predict the axial positions of MP, CP, and MVP with high accuracy. These correlations can be directly applied in engineering design and environmental applications, including the optimization of jet-based cooling configurations, ventilation layouts, and buoyant discharge systems, where a rapid yet reliable estimation of jet interaction characteristics is essential. Compared to isothermal jets (<span><math><mrow><mi>R</mi><mi>i</mi><mo>=</mo><mn>0</mn></mrow></math></span>), buoyant jets show enhanced centreline velocities, stronger recirculation, and reduced lateral dispersion. These findings provide new insights into the coupled momentum and thermal dynamics of TPBJ systems and offer predictive tools for applications in thermal management and environmental jet discharge.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"115 ","pages":"Article 204373"},"PeriodicalIF":2.5,"publicationDate":"2025-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145217833","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Density jump in high-speed Hele-Shaw flows","authors":"Oleg A. Logvinov ,&nbsp;Isabel M. Irurzun","doi":"10.1016/j.euromechflu.2025.204374","DOIUrl":"10.1016/j.euromechflu.2025.204374","url":null,"abstract":"<div><div>We considered the high-speed displacement of fluids from a Hele-Shaw cell where jumps on the interface in both viscosity and density drive the instability and the generation of viscous fingers. Mathematically, the density is a prior factor in the inertial nonlinear terms in the full–averaged Navier–Stokes–Darcy model. Therefore, we investigated the influence of inertial effects on the fingering process. We performed linear stability analysis and numerical simulations by finite–difference method considering dependences on two dimensionless parameters: density ratio and Reynolds number. Two main conclusions could be drawn. The first is that as the Reynolds number increases, the interface becomes more stable in the initial phase of displacement. The second is that the displacement of a denser fluid by a less dense one is more unstable than the opposite case, where a denser fluid displaces a less dense one. We also performed nonlinear simulations that also showed pronounced viscous bubble formation even when the viscosity ratio was relatively small.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"115 ","pages":"Article 204374"},"PeriodicalIF":2.5,"publicationDate":"2025-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145106559","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A physics-embedded Transformer-CNN architecture for data-driven turbulence prediction and surrogate modeling of high-fidelity fluid dynamics","authors":"Sukanta Ghosh ,&nbsp;Vinod Kumar Shukla ,&nbsp;Amar Singh ,&nbsp;Jayanta Chanda","doi":"10.1016/j.euromechflu.2025.204372","DOIUrl":"10.1016/j.euromechflu.2025.204372","url":null,"abstract":"<div><div>Turbulence modeling poses significant challenges due to its nonlinear, multiscale nature. Classical methods like Reynolds-Averaged Navier–Stokes and Large Eddy Simulation often rely on empirical closures, which limit their accuracy in complex flows. This study aims to propose a hybrid model that integrates convolutional neural networks for capturing local spatial patterns with Transformer-based attention modules to model long-range dependencies. The architecture is informed by the Navier–Stokes equations and incorporates divergence-free constraints to preserve physical fidelity. The model is trained and evaluated on direct numerical simulation datasets representing 2D turbulence and turbulent channel flows. The model achieved up to 40 % reduction in prediction error compared to CNN and RNN baselines. It accurately reproduced key flow structures and energy spectra, showing strong agreement with DNS outputs. The hybrid architecture demonstrated stable long-term predictions and matched statistical flow properties over extended time horizons. For steady flows, it corrected RANS-predicted biases in mean velocity profiles with near-exact reconstruction. The results validate the effectiveness of combining physics-informed learning with deep neural architectures. The proposed framework offers a computationally efficient alternative to traditional turbulence models while retaining accuracy, marking a promising advancement in data-driven fluid mechanics.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"115 ","pages":"Article 204372"},"PeriodicalIF":2.5,"publicationDate":"2025-09-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145106556","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"On the stable convection in a differentially spot-heated loop near the temperature of maximum density","authors":"Alexey E. Rastegin","doi":"10.1016/j.euromechflu.2025.204366","DOIUrl":"10.1016/j.euromechflu.2025.204366","url":null,"abstract":"<div><div>Welander’s approach to study convective motions in a differentially spot-heated loop is reformulated for the case of fluid near the temperature of maximum density. The existence of this temperature is of great importance to understand dynamics of temperate lakes. The key character of the case of interest is that heat exchange takes place only within small spots at the bottom and the top of the loop. This study aims to reveal what happens with convective motions when fluid is near a state with the zero coefficient of thermal expansion. A somehow surprising conclusion is that steady regimes of convection, when they exist, turn out to be stable. This outcome differs from the case when heat exchange with the environment in line with Newton’s law of cooling takes place in a whole range of the loop. The findings of theoretical analysis are supported by the results of numerical studies. The reported outcomes allow us to estimate peculiarities of building more complex models of thermal convection. In particular, the role of spot-heated character of exchange with the environment is demonstrated. This feature should be kept in mind in attempts to simulate natural convection on the base of idealized models.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"115 ","pages":"Article 204366"},"PeriodicalIF":2.5,"publicationDate":"2025-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145106558","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Thermohydraulic performance of twisted circular tube (TCT) retrofitted with twisted strip (TS) insert","authors":"Janhavi K. Devnikar,&nbsp;Jayraj M. Chapare,&nbsp;Om M. Butle,&nbsp;P.W. Deshmukh,&nbsp;Pravin R. Kubade,&nbsp;Lalit K. Toke","doi":"10.1016/j.euromechflu.2025.204367","DOIUrl":"10.1016/j.euromechflu.2025.204367","url":null,"abstract":"<div><div>Augmentation of heat transfer plays a crucial role in energy-saving options in modern thermal systems. These enhancement methods are passive with no external power source, and another is an active method where an external energy source is essential. The passive methods are more popular and the best energy-saving option, making the system more effective and efficient. The recent advancement in passive methods is a compound method consisting of alterations in the fluid containers and obstructions in fluid passages. In the prevailing study, the round tube is formed in the profile of a twisted tube, within which a twisted strip is placed. The twisted tube causes a reduction in the temperature and velocity gradients near the tube surface due to the twisting motion of the fluid at that region, whereas the central core portion of the fluid interacts thoroughly with the heated surface due to the presence of the twisted strip at the central portion of the twisted tube. This modified flow system enhanced heat transfer using air as a fluid in turbulent flow circumstances for Reynolds numbers ranging from 2500 to 17000. The present study indicates that the average improvement ratio, <em>Nu</em>_<em>e</em><em>/Nu</em>_<em>p</em><em>,</em> and average friction factor ratio, <em>f</em>_<em>e</em><em>/f</em>_<em>p</em>, are 1.25–3.9 and 2.0–12.0, respectively, compared with the plain tube at the same flow rate conditions.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"115 ","pages":"Article 204367"},"PeriodicalIF":2.5,"publicationDate":"2025-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145106555","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Unsteady aerodynamics of the control of three dimensional flow separation by morphing a wing surface","authors":"Aritras Roy ,&nbsp;Rinku Mukherjee","doi":"10.1016/j.euromechflu.2025.204348","DOIUrl":"10.1016/j.euromechflu.2025.204348","url":null,"abstract":"&lt;div&gt;&lt;div&gt;The ability of a morphed wing to prevent 3D flow separation when operating at high angles of attack and when the flow past it is unsteady is investigated. The wing is morphed using an external skin attached to the leading edge of the wing, which takes the shape of the suction/top surface of the wing, when not in use. When required, the external skin is deployed but with a new shape, which is a morphed version of the top surface of the wing and has the ability to prevent flow separation. The shape of the external skin is predicted using a numerical algorithm developed for this purpose that couples an Unsteady Vortex Lattice Method with another in-house steady-state Vortex Lattice Method algorithm that uses a ‘decambering’ concept to ‘correct’ the local camberline to account for flow separation. Physical wing models are then fabricated along with the numerically predicted morphed surfaces to be attached externally at the leading edge and tested in the wind tunnel. Unsteady change in angle of attack is implemented using an in-house mechanism developed for this purpose, where the rate of change of angle of attack, &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mfrac&gt;&lt;mrow&gt;&lt;mi&gt;∂&lt;/mi&gt;&lt;mi&gt;α&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;∂&lt;/mi&gt;&lt;mi&gt;t&lt;/mi&gt;&lt;/mrow&gt;&lt;/mfrac&gt;&lt;mo&gt;=&lt;/mo&gt;&lt;mover&gt;&lt;mrow&gt;&lt;mi&gt;α&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mo&gt;̇&lt;/mo&gt;&lt;/mrow&gt;&lt;/mover&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; is varied as &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mn&gt;0&lt;/mn&gt;&lt;mo&gt;.&lt;/mo&gt;&lt;mn&gt;1&lt;/mn&gt;&lt;mo&gt;°&lt;/mo&gt;&lt;mo&gt;/&lt;/mo&gt;&lt;mi&gt;s&lt;/mi&gt;&lt;mo&gt;&lt;&lt;/mo&gt;&lt;mover&gt;&lt;mrow&gt;&lt;mi&gt;α&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mo&gt;̇&lt;/mo&gt;&lt;/mrow&gt;&lt;/mover&gt;&lt;mo&gt;&lt;&lt;/mo&gt;&lt;mn&gt;1&lt;/mn&gt;&lt;mo&gt;°&lt;/mo&gt;&lt;mo&gt;/&lt;/mo&gt;&lt;mi&gt;s&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;. Unsteady aerodynamic characteristics like &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;C&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;mrow&gt;&lt;mo&gt;(&lt;/mo&gt;&lt;mi&gt;t&lt;/mi&gt;&lt;mo&gt;)&lt;/mo&gt;&lt;/mrow&gt;&lt;mo&gt;,&lt;/mo&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;C&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;D&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;mrow&gt;&lt;mo&gt;(&lt;/mo&gt;&lt;mi&gt;t&lt;/mi&gt;&lt;mo&gt;)&lt;/mo&gt;&lt;/mrow&gt;&lt;mo&gt;,&lt;/mo&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;C&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;M&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;mrow&gt;&lt;mo&gt;(&lt;/mo&gt;&lt;mi&gt;t&lt;/mi&gt;&lt;mo&gt;)&lt;/mo&gt;&lt;/mrow&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; are measured for change in Reynolds number, &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mn&gt;0&lt;/mn&gt;&lt;mo&gt;.&lt;/mo&gt;&lt;mn&gt;045&lt;/mn&gt;&lt;mo&gt;×&lt;/mo&gt;&lt;mn&gt;1&lt;/mn&gt;&lt;msup&gt;&lt;mrow&gt;&lt;mn&gt;0&lt;/mn&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;6&lt;/mn&gt;&lt;/mrow&gt;&lt;/msup&gt;&lt;mo&gt;&lt;&lt;/mo&gt;&lt;mi&gt;R&lt;/mi&gt;&lt;mi&gt;e&lt;/mi&gt;&lt;mo&gt;&lt;&lt;/mo&gt;&lt;mn&gt;0&lt;/mn&gt;&lt;mo&gt;.&lt;/mo&gt;&lt;mn&gt;1&lt;/mn&gt;&lt;mo&gt;×&lt;/mo&gt;&lt;mn&gt;1&lt;/mn&gt;&lt;msup&gt;&lt;mrow&gt;&lt;mn&gt;0&lt;/mn&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;6&lt;/mn&gt;&lt;/mrow&gt;&lt;/msup&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;. Flow visualization using smoke is conducted in the wind tunnel. CFD is also used to study such a morphing wing at high angles of attack including at post-stall. Spectral densities of the transient load data, &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;C&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;mrow&gt;&lt;mo&gt;(&lt;/mo&gt;&lt;mi&gt;t&lt;/mi&gt;&lt;mo&gt;)&lt;/mo&gt;&lt;/mrow&gt;&lt;mo&gt;,&lt;/mo&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;C&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;D&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;mrow&gt;&lt;mo&gt;(&lt;/mo&gt;&lt;mi&gt;t&lt;/mi&gt;&lt;mo&gt;)&lt;/mo&gt;&lt;/mrow&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; and unsteady sectional lift coefficient, &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;C&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;l&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;s&lt;/mi&gt;&lt;mi&gt;e&lt;/mi&gt;&lt;mi&gt;c&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;mrow&gt;&lt;mo&gt;(&lt;/mo&gt;&lt;mi&gt;t","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"115 ","pages":"Article 204348"},"PeriodicalIF":2.5,"publicationDate":"2025-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145026327","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Role of insoluble surfactant on electrohydrodynamic stability of a two-layer plane Poiseuille flow: An asymptotic analysis","authors":"Sarita Yadav,&nbsp;Geetanjali Chattopadhyay","doi":"10.1016/j.euromechflu.2025.204356","DOIUrl":"10.1016/j.euromechflu.2025.204356","url":null,"abstract":"<div><div>The electrohydrodynamic stability of a two-layer plane Poiseuille flow has been considered under the influence of an electric field acting normally to the interface of the two viscous immiscible fluids. The two fluids considered here for the asymptotic stability analysis are leaky dielectrics. The study on the influence of a monolayer of insoluble surfactant at the fluid-fluid interface reveals that the interfacial surfactant further enhances or suppresses the electric field-induced instability. The long-wave linear stability analysis is carried out in the framework of Orr–Sommerfeld analysis for leaky dielectrics. In the context of long-wave linear stability study, the phase speed is expressed as a function of the ratio of viscosities (<span><math><mi>m</mi></math></span>), layer thicknesses (<span><math><mi>d</mi></math></span>), densities (<span><math><mi>r</mi></math></span>), permittivities (<span><math><mi>ɛ</mi></math></span>) and conductivities (<span><math><mi>l</mi></math></span>) of the two fluids. The electric field is observed to have either a destabilizing or a stabilizing effect, primarily non-monotonic, depending upon the ratios of permittivities and conductivities of the two fluids. It is found that when <span><math><mrow><mi>m</mi><mo>&gt;</mo><msup><mrow><mi>d</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math></span>, the region of instability in the <span><math><mrow><mi>ɛ</mi><mo>−</mo><mi>l</mi></mrow></math></span> plane increases with increasing Marangoni number (<span><math><mrow><mi>M</mi><mi>a</mi></mrow></math></span>); however, when <span><math><mrow><mi>m</mi><mo>&lt;</mo><msup><mrow><mi>d</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math></span>, the scenario reverses. The electrohydrodynamic interface instability among two viscous fluids with varying electrical properties in plane Poiseuille flow has applications in microfluidic devices for mixing and droplet formation. Therefore, the present study aims to propose a control mechanism for the instability occurring at the interface through the modified interface tension.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"115 ","pages":"Article 204356"},"PeriodicalIF":2.5,"publicationDate":"2025-09-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145047215","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}