European Journal of Mechanics B-fluids最新文献

{"title":"Linear and nonlinear stability analysis of thermotactic bioconvection","authors":"Keshav Singh ,&nbsp;Y.D. Sharma ,&nbsp;Sanjalee Maheshwari","doi":"10.1016/j.euromechflu.2026.204481","DOIUrl":"10.1016/j.euromechflu.2026.204481","url":null,"abstract":"<div><div>Thermotactic microorganisms are motile organisms that migrate in response to temperature gradients, exhibiting movement toward heat sources. Understanding thermotaxis is vital for advancements in biotechnology, wastewater treatment, and medical microbiology. In this study, the onset of bioconvection in a fluid layer containing thermotactic microorganisms is investigated through both linear and nonlinear stability analysis under free–free boundary conditions. The linear stability analysis is carried out by introducing infinitesimal perturbations and applying the normal mode technique, resulting in an eigenvalue problem. For the nonlinear analysis, an energy method is employed. A variational formulation is developed, which is further used to derive an eigenvalue problem. The obtained eigenvalue problems is finally solved using the Galerkin technique. A comparative study between the linear and nonlinear results is performed to highlight the differences in critical thresholds. The findings indicate that the Péclet number destabilizes the system, and as its value increases, the subcritical region of instability decreases. Furthermore, stronger thermal effects lead to an earlier onset of bioconvection, characterized by a reduction in the critical bioconvection Rayleigh number. These insights can aid in the practical design and control of bioconvective systems in bioengineering, environmental treatment processes, and industrial fluid technologies.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"118 ","pages":"Article 204481"},"PeriodicalIF":2.5,"publicationDate":"2026-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146074606","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 road determination of vehicle drag coefficient using the new constant power plate method","authors":"Michael Gerard Connolly,&nbsp;Alojz Ivankovic,&nbsp;Malachy J. O’Rourke","doi":"10.1016/j.euromechflu.2026.204465","DOIUrl":"10.1016/j.euromechflu.2026.204465","url":null,"abstract":"<div><div>This paper presents a novel on-road method for determining a vehicle’s aerodynamic drag coefficient using a constant power approach with a towbar-mounted drag plate. The technique involves fixing the throttle pedal and measuring the vehicle’s equilibrium speeds in two configurations: baseline and with the added drag plate. From these speeds, the vehicle’s baseline drag coefficient can be calculated. Two formulations are introduced — one for an idealised plate with negligible self and interference drag, and another for practical setups where the support structure introduces additional self-drag and interference. The method was applied to a Citroen Berlingo van using an aluminium plate and stand, yielding a measured drag coefficient of 0.416. Validation against traditional coastdown testing showed a close agreement, with only a 6.1% difference. A sensitivity analysis demonstrated that the new method is less dependent on variables such as vehicle mass, air density and rolling resistance compared to coastdown testing. The potential to extend the method to estimate a vehicle’s rolling resistance is discussed, though limited by current GPS accuracy. Overall, the new constant power plate method offers a simple, robust alternative to coastdown testing and demonstrates strong potential for its usage in future aerodynamic assessment and vehicle development.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"118 ","pages":"Article 204465"},"PeriodicalIF":2.5,"publicationDate":"2026-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146035443","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":"Effect of bend radius on gas slug formation mechanisms in air–water two-phase flow within a horizontal minichannel T-junction","authors":"Untung Surya Dharma ,&nbsp;Syaiful Tambah Putra Ahmad ,&nbsp;Indarto ,&nbsp;Deendarlianto","doi":"10.1016/j.euromechflu.2026.204475","DOIUrl":"10.1016/j.euromechflu.2026.204475","url":null,"abstract":"<div><div>The bend radius of a T-junction significantly affects local flow dynamics by altering the velocity distribution downstream of the junction. A larger bend radius reduces local vortices, accelerates uniform flow development, and modifies the mechanism of initial gas slug formation. This study investigates the influence of bend radius on initial gas slug formation in a rectangular acrylic T-junction minichannel with a hydraulic diameter (<em>D</em>_<em>h</em>) of 1.6 mm, and three bend radius ratios (<em>r/D</em>_<em>h</em> = 0.5, 0.7, and 1.0). Air and water were used as working fluids. Water superficial velocity (<em>J</em>_<em>l</em>) ranged from 0.626 to 3.186 m·s⁻¹, and air superficial velocity (<em>J</em>_<em>g</em>) from 0.593 to 2.371 m·s⁻¹. Flow formation was analysed using high-speed imaging at 15,000 frames per second, and pressure fluctuations were recorded at 15,000 Hz. Three distinct regimes were identified: shearing (SR), shearing–dripping (SDR), and squeezing (SQR), each characterised by unique stage sequences and pressure fluctuation patterns. In SR and SDR, the formation time (<em>T</em>_<em>s</em>) consists of necking, filling, and pinch-off; in SQR, <em>T</em>_<em>s</em> comprises pressure build-up, filling, and squeezing. Results show that increasing <em>r/D</em>_<em>h</em> enhances gas slug growth velocity (<em>U</em>_<em>s</em>) and frequency (<em>f</em>_<em>r</em>) while reducing gas slug length (<em>L</em>_<em>s</em>). The proposed non-dimensional <em>U</em>_<em>s</em><em>/Jₗ</em> correlation predicts experimental results with a Mean Absolute Percentage Error (MAPE) of ±5 %. In addition, the <em>f</em>_<em>r</em> is generalised using the Strouhal number (<em>St</em>)–Capillary number (<em>Ca</em>) framework, which highlights the combined effects of viscous–capillary dynamics and geometrical control on gas slug formation. Flow pattern maps, constructed from experimental observations and artificial neural network (ANN) predictions, showed up to 91.5 % agreement across all <em>r/Dₕ</em>. This work provides experimental evidence that bend radius governs gas slug initiation dynamics, offering design guidelines for multiphase flow control in chemical and biomedical applications.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"118 ","pages":"Article 204475"},"PeriodicalIF":2.5,"publicationDate":"2026-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146035441","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 on friction factor of rectangular mini-channel with staggered Pin-Fin: Effects of pitch geometry","authors":"Armanto Pardamean Simanjuntak,&nbsp;Ahn Taemin,&nbsp;Joohan Bae,&nbsp;Jae Young Lee","doi":"10.1016/j.euromechflu.2026.204482","DOIUrl":"10.1016/j.euromechflu.2026.204482","url":null,"abstract":"<div><div>This study presents a comprehensive numerical investigation of friction-factor behavior in staggered square pin-fin minichannels across a wide Reynolds-number range (30 ≤ <em>Re</em> ≤7000). Three geometric configurations defined by the spacing ratio <em>SH/S</em>= 0.5, 1, 2 were evaluated to quantify the influence of pin spacing on pressure drop, flow development, and turbulence onset. The simulations employed the <em>k-ε</em> model with enhanced wall treatment, with near-wall resolution verified through y + analysis and a mesh-independence assessment supported by the Grid Convergence Index. Results show that all geometries exhibit a smooth, monotonic transition from laminar to turbulent flow without a distinct transition point, owing to the strong disturbance induced by the staggered pin arrangement. Flow visualization confirms attached flow at low Reynolds numbers and progressively stronger recirculation and vortex structures as inertia increases, with the densest spacing (<em>SH/S</em>=0.5)producing the highest turbulence intensity and hydraulic resistance. Based on the numerical database, a new friction-factor correlation was developed. Regime-specific expressions were first obtained for laminar, transitional, and turbulent regions, after which the geometric effects were generalized through a power-law dependence on <em>SH/S</em>. These expressions were consolidated into a single unified correlation using a maximum-based blending approach. Validation against CFD data demonstrates deviations below 10 % across all spacing ratios and flow regimes. The proposed correlation provides an accurate and practical predictive tool for pressure-loss estimation in compact heat exchangers and thermal management systems employing staggered square pin-fin structures.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"118 ","pages":"Article 204482"},"PeriodicalIF":2.5,"publicationDate":"2026-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146185040","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":"Instability of plane Couette flow under competing effects of viscoelasticity and vertical throughflow","authors":"B.M. Shankar ,&nbsp;I.S. Shivakumara","doi":"10.1016/j.euromechflu.2026.204477","DOIUrl":"10.1016/j.euromechflu.2026.204477","url":null,"abstract":"<div><div>The linear instability of plane laminar flow of a Navier–Stokes–Voigt fluid between parallel plates in relative motion with a uniform vertical throughflow is analysed. The validity of Squire’s theorem is established, thereby justifying restriction to two-dimensional spanwise-independent perturbations. The resulting continuous eigenvalue problem is discretized using the Chebyshev collocation method, yielding a generalized matrix eigenvalue problem that is solved numerically to determine the stability thresholds. The critical Reynolds number marking the onset of instability is computed for different values of the throughflow-dependent Reynolds number and the Kelvin–Voigt viscoelastic parameter. A key finding of the analysis is the appearance of bimodal neutral stability curves within limited parameter ranges, accompanied by branch-to-branch transitions in which the dominant instability changes identity—a feature absent when either mechanism acts in isolation. The results further reveal that throughflow may be stabilizing, destabilizing, or even produce mixed behavior, depending strongly on the strength of viscoelastic effects. Streamline visualizations at criticality uncover the formation of complex, spatially structured flow fields, highlighting the intricate dynamics driven by the interplay between viscoelasticity and throughflow.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"118 ","pages":"Article 204477"},"PeriodicalIF":2.5,"publicationDate":"2026-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146185041","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":"Droplet transport, merging and splitting based on combined wettability-confined tracks","authors":"Xiaojin Fu ,&nbsp;Da Xu ,&nbsp;Junxiong Zeng ,&nbsp;Guangtao Zhai","doi":"10.1016/j.euromechflu.2026.204476","DOIUrl":"10.1016/j.euromechflu.2026.204476","url":null,"abstract":"<div><div>Wettability-confined tracks enable rapid spontaneous droplet transport, providing an effective manipulation platform for open-surface microfluidic systems. In this study, a series of combined wettability-confined tracks is designed to achieve complex droplet manipulation, including long-distance transport, merging and splitting. The lattice Boltzmann method is used to study the droplet dynamic behaviors. First, the validity of the model has been verified by simulating the dynamic partial wetting process and coalescence of adjacent stationary droplets. Then, the droplet spreading behaviors on the designed surfaces are systematically investigated. Serial tracks enable the long-distance transportation of droplets, and the constriction ratio at the junction regions serves as the critical factor determining the feasibility of sustained long-range transport. Both T-shaped tracks and combined parallel tracks are designed to achieve droplet merging effectively, and the morphological evolution of droplets during the merging process is revealed. The centrally symmetrical track pattern can realize the droplet splitting in equal volumes to eliminate the cross-contamination of reagents. These designs offer a versatile strategy for advanced droplet-based operations.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"118 ","pages":"Article 204476"},"PeriodicalIF":2.5,"publicationDate":"2026-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146035442","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":"Lattice Boltzmann modeling of gas-liquid absorption reactions in a microchannel","authors":"Mingyuan Wang ,&nbsp;Ning Zhang ,&nbsp;Hong Zhang ,&nbsp;Wei Zhang ,&nbsp;Wenjin Zhou ,&nbsp;Muxuan Qin","doi":"10.1016/j.euromechflu.2026.204487","DOIUrl":"10.1016/j.euromechflu.2026.204487","url":null,"abstract":"<div><div>The Lattice Boltzmann Method (LBM) offers distinct advantages in simulating multiphase fluid flows at mesoscales, especially for microchannel applications. This paper establishes a multiphase flow model with thermodynamic consistency and independently adjustable surface tension under large density ratios. Based on this, the LBM multiphase multicomponent flow model is combined with the CST-LBM mass transfer model and the Arrhenius-format reaction source term to achieve an accurate description of the complex mass transfer behavior at phase interfaces during gas-liquid absorption reactions. The accuracy of the LBM model is validated through theoretical analysis based on Laplace's law and the convection-diffusion-reaction equations. The model was applied to simulate the reaction process of ethanolamine solution absorbing carbon disulfide in a microchannel, and the influence patterns of gas flow rate, droplet radius, and channel width on the reaction were investigated. The results indicate that the LBM model established in this study can accurately simulate the absorption reaction process of multi-phase, multi-component fluids in microchannels, providing an effective numerical simulation model for green chemical absorption research in microreactors.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"118 ","pages":"Article 204487"},"PeriodicalIF":2.5,"publicationDate":"2026-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146184959","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":"Vorticity-dependent and symmetry-preserving LES models","authors":"Oscar Cosserat ,&nbsp;Dina Razafindralandy ,&nbsp;Can Selçuk","doi":"10.1016/j.euromechflu.2026.204478","DOIUrl":"10.1016/j.euromechflu.2026.204478","url":null,"abstract":"<div><div>Within the Large Eddy Simulation framework, we propose a methodology based on the Lie theory to derive symmetry-preserving turbulence models. We apply this methodology to the incompressible Navier–Stokes equations. These models explicitly depend on both the filtered strain-rate tensor and the filtered vorticity tensor. Particular emphasis is placed on models that additionally ensure stability.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"118 ","pages":"Article 204478"},"PeriodicalIF":2.5,"publicationDate":"2026-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146074604","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":"Comments about Davey et al. [1] A two-experiment approach to hydraulic jump scaling","authors":"Valentin Heller","doi":"10.1016/j.euromechflu.2026.204479","DOIUrl":"10.1016/j.euromechflu.2026.204479","url":null,"abstract":"<div><div>These Comments address the paper by K. Davey, A. Al-Tarmoom, H. Sadeghi, A two-experiment approach to hydraulic jump scaling, Eur. J. Mech. B Fluids, 111(3) (2025) 215–228 [1], from the perspective of practical hydraulics. The modelling and scaling of complex fluid flows at reduced size, including hydraulic jumps, are explained in more detail. Particular attention is given to the Froude scaling laws, which correspond to some of the scaling relations derived in Ref. [1]. The discussion then extends to alternative theoretical and empirical approaches to address scale effects in hydraulics, in addition to the finite similitude scaling theory [1]. These include precise Froude scaling, one-parameter Lie group point-scaling transformations, Reynolds number invariance, numerical quantification of scale effects and the scale series method. Finally, possible future research paths, building upon the work in Ref. [1], are outlined.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"118 ","pages":"Article 204479"},"PeriodicalIF":2.5,"publicationDate":"2026-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146074607","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":"High-fidelity actuator line large eddy simulations of multi-turbine VAWT clusters under varying geometric configurations","authors":"Prathamesh Banda,&nbsp;Mayank Verma ,&nbsp;D.V.G. Prasad,&nbsp;Ashoke De","doi":"10.1016/j.euromechflu.2026.204462","DOIUrl":"10.1016/j.euromechflu.2026.204462","url":null,"abstract":"<div><div>This study investigates the aerodynamic performance of VAWT clusters under varying array geometries. Staggered V-shaped clusters of vertical-axis wind turbines (VAWTs) are examined to assess aerodynamic interactions in compact wind farm layouts. Configurations use six UNH-RVAT reference turbines, with variations in cluster angle, streamwise spacing, and turbine count. High-fidelity actuator-line large-eddy simulations (LES) are performed using a modified Xcompact3D solver. A six-turbine cluster is analyzed for cluster angles of 20°, 30°, and 45° and streamwise spacings of 2D and 3D (two or three rotor diameters). Results are compared to a reduced five-turbine cluster. Cluster angle strongly affects wake overlap and power capture. At a narrow angle (20°), wake shielding is severe and downstream output is lowered, whereas a wide angle (45°) improves wake recovery but reduces upstream synergy. The intermediate angle (30°) yields the highest overall array performance by balancing these effects. Increased streamwise spacing (3D vs 2D) markedly enhances wake recovery and significantly raises downstream turbine efficiency. Reducing the turbine count from six to five further alleviates wake losses, resulting in higher average power coefficients and more uniform inflow. Flow-field diagnostics (velocity, vorticity, kinetic energy deficit) confirm these trends. These results provide design guidelines: optimizing cluster angle, spacing, and turbine count can substantially improve the efficiency and robustness of high-density VAWT arrays.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"118 ","pages":"Article 204462"},"PeriodicalIF":2.5,"publicationDate":"2026-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145974734","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}