European Journal of Mechanics B-fluids最新文献

{"title":"Wake characteristics at the fin tip streamwise cross-section of a manta robot","authors":"Tian Bao ,&nbsp;Ya Zhang ,&nbsp;Qiaogao Huang","doi":"10.1016/j.euromechflu.2026.204472","DOIUrl":"10.1016/j.euromechflu.2026.204472","url":null,"abstract":"<div><div>Mantas exhibit significant deformation at the fin tip during swimming, which results in remarkable hydrodynamic performance. To investigate the wake characteristics at the streamwise tip cross-section of a manta robot, we have developed an experimental platform that utilizes a Particle Image Velocimetry (PIV) system. The physical and geometric characteristics of the wake vortex at the fin tip are analyzed when varying motion parameters and flow velocity conditions. Results indicate that the vortex flux in the wake decreases over time, with attenuation exceeding 50 % by the fifth vortex, while the vortex core area initially increases, reaching a peak at a characteristic length of 3.0 with a 35 % increase before subsequently decreasing. Moreover, only the first two vortices contribute to propulsion momentum. Similarly, the propulsion performance of the single-bone fins is comparable to that of the double-bone designs. Furthermore, the Strouhal number (St) significantly influences the wake dynamics: when St is within [0.2, 0.4], effective wake jets develop, and efficient propulsion appears with St located in [0.37, 0.44], where the jet angle and momentum angle align, thus optimizing hydrodynamic performance. Sensitivity analysis further confirms that amplitude and frequency are the most influential parameters on vortex momentum, while phase difference plays a key role on propulsion efficiency.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"118 ","pages":"Article 204472"},"PeriodicalIF":2.5,"publicationDate":"2026-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146035435","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":"SQG point vortex dynamics with order Rossby corrections","authors":"Mac Lee ,&nbsp;Stefan G. Llewellyn Smith","doi":"10.1016/j.euromechflu.2026.204467","DOIUrl":"10.1016/j.euromechflu.2026.204467","url":null,"abstract":"<div><div>Quasi-geostrophic flow is an asymptotic theory for flows in rotating systems that are in geostrophic balance to leading order. It is characterised by the conservation of (quasi-geostrophic) potential vorticity and weak vertical flows. Surface quasigeostrophy (SQG) is the special case when the flow is driven by temperature anomalies at a horizontal boundary. The next-order correction to QG, QG+, takes into account ageostrophic effects. We investigate point vortex dynamics in SQG+, building on the work of Weiss (2022). The conservation laws for SQG point vortices that parallel the 2D Euler case no longer exist when ageostrophic effects are included. The trajectories of point vortices are obtained explicitly for the general two-vortex case in SQG and SQG+. For the three-vortex case, exact solutions are found for rigidly rotating and stationary equilibria consisting of regular polygons and collinear configurations. As in the 2D case, only certain collinear vortex configurations are rigid equilibria. Trajectories of passive tracers advected by point vortex systems are studied numerically, in particular their vertical excursions, which are non-zero because of ageostrophic effects. Surface trajectories can manifest local horizontal divergence even though the underlying fluid equations are incompressible.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"118 ","pages":"Article 204467"},"PeriodicalIF":2.5,"publicationDate":"2026-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146035437","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 research on 2D wall-driven cavity flows: A review for Hopf bifurcation and steady vortical structures","authors":"B. An ,&nbsp;K.D. Chen ,&nbsp;P.H. Song ,&nbsp;Y.K. Guan ,&nbsp;X. Hu","doi":"10.1016/j.euromechflu.2026.204471","DOIUrl":"10.1016/j.euromechflu.2026.204471","url":null,"abstract":"<div><div>The study of Hopf bifurcation and vortex evolution of cavity flows represents a critical frontier in fluid dynamics, with broad implications for both fundamental science and engineering applications. A comprehensive review on the cavity flows regarding the flow instability, flow patterns, and vortical evolution is performed in the present study, which is focused on the analysis of fluid mechanism induced by the onset of flow instability, explaining the corresponding flow phenomena. Through an extensive literature review and a thorough comparison study, based on the authors’ numerical studies, we have revealed the complex influence of the cavity geometries and driving conditions on the critical Reynolds numbers of Hopf bifurcation and steady vortical structures of two-dimensional wall-driven cavity flows. The summaries in this paper are of great significance for a comprehensive and in-depth understanding of the nature of the shear-driven confined internal flows, underlying the complex interplay of turbulence, flow separation, vortex dynamics, and secondary flows within confined enclosures. It serves as important theoretical foundation of engineering applications and the validations of novel advanced mathematical model and numerical algorithms for the entire scientific community.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"118 ","pages":"Article 204471"},"PeriodicalIF":2.5,"publicationDate":"2026-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146035445","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":"Continuum or individual models for suspensions of swimming micro-organisms?","authors":"T.J. Pedley","doi":"10.1016/j.euromechflu.2026.204484","DOIUrl":"10.1016/j.euromechflu.2026.204484","url":null,"abstract":"<div><div>This article will track the fluid mechanics of collective behaviour in suspensions of swimming microorganisms from the beginning of the author’s collaboration with the late John Kessler in 1984, concentrating exclusively on motile algae, especially those that are bottom-heavy, so they swim upwards, and denser than water. Kessler’s laboratory experiments revealed bioconvection patterns in shallow chambers, and population focussing on the axis of downward pipeflow due to gyrotaxis. We developed a continuum model to explain the observations and this proved qualitatively and to some extent quantitatively, very satisfactory. However, the model incorporates a number of simplifying assumptions, which will be questioned and those that need to be modified (or abandoned) will be identified. In particular, when a suspension is not dilute, so that hydrodynamic cell–cell interactions are significant, the continuum model must be replaced by an individual-based model, and when applying a model to a suspension of real microorganisms in the presence of rigid boundaries, we need to enquire what boundary conditions should be applied to individual swimmers as well as collections of them. Recent results that will be discussed include (a) the prediction of negative apparent viscosity in suspensions of upswimming, bottom-heavy puller squirmers (not pushers) and (b) the observation that certain algal cells respond to the presence of a wall when they appear to be too far from it for contact, or even hydrodynamic interaction, to be possible.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"118 ","pages":"Article 204484"},"PeriodicalIF":2.5,"publicationDate":"2026-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146184960","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":"Sensitivity analysis of Navier–Stokes equations with heat transfer using the first-order polynomial chaos method and FEV discretization","authors":"N. Nouaime ,&nbsp;B. Després ,&nbsp;M.A. Puscas ,&nbsp;C. Fiorini","doi":"10.1016/j.euromechflu.2025.204430","DOIUrl":"10.1016/j.euromechflu.2025.204430","url":null,"abstract":"<div><div>This paper uses the intrusive polynomial chaos method (IPCM) to analyze sensitivity in heat transfer problems governed by the Navier–Stokes equations with heat transfer. The intrusive polynomial chaos method incorporates uncertain variables as combinations of orthogonal polynomials, known as polynomial chaos expansions (PCEs), directly into the governing equations. This transformation turns the original deterministic PDEs into coupled deterministic equations for the PCE coefficients. We apply first-order IPCM and propose a decoupling approach for state and sensitivity systems. We discretize the state equations and their sensitivity using the Finite Element-Volume (FEV) method. We establish a stability estimate for the continuous and discrete state and sensibility equations.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"118 ","pages":"Article 204430"},"PeriodicalIF":2.5,"publicationDate":"2026-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145923772","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":"Finite element analysis of viscous flow around Julia fractals based on comparative study of San Marco and Siegel disk geometries","authors":"Zafar Hayat Khan ,&nbsp;Waqar Ahmed Khan ,&nbsp;Alexander Trounev ,&nbsp;Li-Bin Liu","doi":"10.1016/j.euromechflu.2026.204470","DOIUrl":"10.1016/j.euromechflu.2026.204470","url":null,"abstract":"<div><div>This study presents a finite element investigation of laminar viscous flow around two Julia-set-based fractals: the San Marco and the Siegel disk. The analysis focuses on the influence of multi-scale boundary complexity on aerodynamic behavior. Simulations are conducted for Reynolds numbers (<span><math><mrow><mi>Re</mi><mo>=</mo><mn>20</mn><mtext>-</mtext><mn>260</mn></mrow></math></span>) using the unsteady incompressible Navier–Stokes equations solved through the finite element method (FEM) implemented in <em>Wolfram Mathematica</em>. Flow visualization and quantitative analysis reveal significant differences in wake topology between the two fractal configurations. The symmetric San Marco fractal exhibits a stabilized wake and a moderate drag coefficient (<span><math><mrow><msub><mrow><mi>C</mi></mrow><mrow><mi>D</mi></mrow></msub><mo>≈</mo><mn>5.01</mn></mrow></math></span> at <span><math><mrow><mi>Re</mi><mo>=</mo><mn>20</mn></mrow></math></span>), slightly lower than that of a canonical circular cylinder (<span><math><mrow><msub><mrow><mi>C</mi></mrow><mrow><mi>D</mi></mrow></msub><mo>≈</mo><mn>5.57</mn><mtext>-</mtext><mn>5.59</mn></mrow></math></span>). In contrast, the asymmetric Siegel disk fractal generates a strong negative lift (<span><math><mrow><msub><mrow><mi>C</mi></mrow><mrow><mi>L</mi></mrow></msub><mo>≈</mo><mo>−</mo><mn>2.52</mn></mrow></math></span> at <span><math><mrow><mi>Re</mi><mo>=</mo><mn>240</mn></mrow></math></span>) and achieves further drag reduction (<span><math><mrow><msub><mrow><mi>C</mi></mrow><mrow><mi>D</mi></mrow></msub><mo>≈</mo><mn>2.58</mn></mrow></math></span>) at higher Reynolds numbers, accompanied by intensified wake unsteadiness and an increased pressure loss (<span><math><mrow><mi>Δ</mi><mi>p</mi><mo>≈</mo><mn>13.98</mn></mrow></math></span> at <span><math><mrow><mi>Re</mi><mo>=</mo><mn>260</mn></mrow></math></span>). A distinct transitional regime occurs between <span><math><mrow><mi>Re</mi><mo>=</mo><mn>60</mn><mspace></mspace></mrow></math></span> and <span><math><mrow><mi>Re</mi><mo>=</mo><mn>100</mn></mrow></math></span>, followed by partial recovery of steady flow for the Siegel disk fractal at <span><math><mrow><mi>Re</mi><mo>=</mo><mn>200</mn><mtext>-</mtext><mn>220</mn></mrow></math></span>. These findings demonstrate that fractal-induced multi-scale boundaries modulate shear layers, suppress vortex shedding, and alter drag–lift characteristics, offering new design strategies for passive flow control in laminar and transitional regimes.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"118 ","pages":"Article 204470"},"PeriodicalIF":2.5,"publicationDate":"2026-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146035444","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 bubble rising behavior in viscoelastic fluids via smoothed particle hydrodynamics","authors":"Xiaoyang Xu ,&nbsp;Erdi Wang ,&nbsp;Sai Peng ,&nbsp;Peng Yu","doi":"10.1016/j.euromechflu.2026.204480","DOIUrl":"10.1016/j.euromechflu.2026.204480","url":null,"abstract":"<div><div>This article presents an improved smoothed particle hydrodynamics (SPH) method for investigating the rising behavior of bubbles in viscoelastic fluids, where the viscoelastic characteristic is described by a branched polymer melt model. To enhance the computational accuracy of the SPH method, a kernel gradient correction algorithm is implemented. A particle shifting technique is employed to maintain uniform particle distribution. An interfacial repulsion force is added to ensure numerical stability and accurate representation of phase interface. The proposed SPH method is first validated using two benchmark cases: the rise of a single bubble in a Newtonian fluid and the impact of a viscoelastic droplet on a solid wall. Comparisons between the SPH results and those from other numerical methods reveal good agreement. The method is then extended to simulate the rise of a single bubble in a viscoelastic fluid, with its convergence evaluated using three different particle sizes. The effects of the Reynolds number, Weissenberg number, polymer-to-solvent viscosity ratio, and other parameters on bubble rising behavior are further analyzed. Finally, the method is applied to simulate the rising dynamics of dual bubbles in viscoelastic fluids. The simulation results show that the proposed SPH method is accurate and stable and can investigate the complex dynamics of single and dual bubbles in viscoelastic fluids across a broad range of physical parameters, thereby elucidating the interplay between fluid elasticity and bubble motion.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"118 ","pages":"Article 204480"},"PeriodicalIF":2.5,"publicationDate":"2026-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146185038","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":"Parametric hydrodynamic analysis of ventilated supercavity dynamics under free-surface interaction: Combined effects of submergence depth, Froude number, and air entrainment","authors":"Mohammad-Reza Erfanian,&nbsp;Ali-Akbar Moltani,&nbsp;Mahmood Pasandideh-Fard","doi":"10.1016/j.euromechflu.2026.204485","DOIUrl":"10.1016/j.euromechflu.2026.204485","url":null,"abstract":"<div><div>Ventilated supercavitation involves enveloping a submerged high-speed body within an artificially generated air supercavity to drastically reduce hydrodynamic resistance. Investigating such flows near the free surface is essential due to the interaction between supercavity dynamics and free surface condition at different flow specifications. This work numerically studies the effect of the submergence depth, Froude number, and ventilation rate on the flow characteristics of a disk-cavitator body in ventilated cavitating flow. The simulation is executed using the finite volume-based commercial package ANSYS CFX 15, and accuracy of the simulation predictions are validated by comparison with corresponding experimental data. The results indicate that, unlike typical surface bodies where drag decreases with depth, the drag coefficient of the model with a disk-shaped cavitator under ventilated supercavitation increases with depth. Supercavity shape analyses further show that proximity to the free surface leads to shorter and wider cavities, while deeper submergence results in longer and more slender cavity forms. Moreover, the drag coefficient decreases with increasing Froude number, reflecting reduced wave-making effects. Higher ventilation rates also produce larger supercavities in both length and diameter, with more pronounced effects at lower depths.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"118 ","pages":"Article 204485"},"PeriodicalIF":2.5,"publicationDate":"2026-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146184961","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":"Application of wall functions for investigating surface roughness effects on spreading of an impacting droplet","authors":"Arda Cetiner ,&nbsp;Mete Budakli","doi":"10.1016/j.euromechflu.2026.204468","DOIUrl":"10.1016/j.euromechflu.2026.204468","url":null,"abstract":"<div><div>The spreading dynamics of droplet impact on a solid surface is of great importance in applications such as printing, spray cooling, coating process and anti-icing. These phenomena have been studied in several investigations and aspects such as the effect of critical Weber number on droplet break-up or the air bubble entrainment phenomenon as well as the influence of surface roughness. While experimental studies using surface roughness values ranging from <span><math><mrow><msub><mrow><mi>R</mi></mrow><mrow><mi>a</mi></mrow></msub><mo>=</mo><mn>0</mn><mo>.</mo><mn>003</mn><mspace></mspace><mi>μ</mi><mi>m</mi></mrow></math></span> to <span><math><mrow><mn>25</mn><mspace></mspace><mi>μ</mi><mi>m</mi></mrow></math></span> were conducted, a few analytical approaches are available taking into account roughness effects in correlations. Contrary to this, considering roughness physically in simulations requires large calculation capability, time for geometry preparation as well as the reconstruction of varying topographical combinations is rather difficult and needs to be elaborated broadly. Therefore, the present study recommends a time-saving approach in OpenFOAM in which surface roughness is not represented physically in the domain, rather taken into account in a wall function term. The results of the study are in good agreement of <span><math><mrow><mo>±</mo><mn>10</mn><mtext>%</mtext></mrow></math></span> with the experimental data and mathematical models found in literature. Single drop impact simulations were carried out over a range of Weber number from 106 to 298 indicate that as <em>We</em> number increases, the effect of the surface roughness on the spreading process diminishes.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"118 ","pages":"Article 204468"},"PeriodicalIF":2.5,"publicationDate":"2026-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146035440","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":"Modulating cerebrospinal fluid flow by magnetohydrodynamic force","authors":"Mohammad Shamsodini Lori ,&nbsp;Seyed Farzad Maroufi ,&nbsp;Mohamad Ali Bijarchi ,&nbsp;Mark G. Luciano ,&nbsp;Zohreh Habibi ,&nbsp;Jiangtao Cheng","doi":"10.1016/j.euromechflu.2025.204424","DOIUrl":"10.1016/j.euromechflu.2025.204424","url":null,"abstract":"<div><div>Approximately one in 20,000 individuals experiences a neurological disorder each year due to disturbances in cerebrospinal fluid (CSF) flow within the brain's ventricles. Consequently, developing treatment methods to modify and regulate CSF flow is crucial for addressing these dilemmas. In this study, the effect of MagnetoHydroDynamic (MHD) force on the fluid flow characteristics of CSF inside a three-dimensional (3D) model of the Cerebral Ventricular System (CVS) is numerically investigated. Magnetic Resonance Imaging (MRI) is employed to rebuild the brain's geometry via image reconstruction software. Both invasive methods, which involve inserting electrodes and magnets into the brain, and non-invasive methods, which involve placing electrodes and magnets on the brain's surface, are studied numerically. The results of these two methods are then compared. Under MHD force, the pressure inside the third and lateral ventricles is reduced by 18 %. Additionally, there is a significant local increase in the CSF transportation speed from the third ventricle to the fourth ventricle. Furthermore, incorporating nanoparticles (NPs) strengthens the MHD force, resulting in an increased pressure differential between the third and fourth ventricles.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"117 ","pages":"Article 204424"},"PeriodicalIF":2.5,"publicationDate":"2026-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145683172","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}