Pub Date : 2026-01-17DOI: 10.1016/j.euromechflu.2026.204465
Michael Gerard Connolly, Alojz Ivankovic, Malachy J. O’Rourke
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.
{"title":"On road determination of vehicle drag coefficient using the new constant power plate method","authors":"Michael Gerard Connolly, Alojz Ivankovic, 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":"2026-01-17","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}
Pub Date : 2026-01-17DOI: 10.1016/j.euromechflu.2026.204472
Tian Bao , Ya Zhang , Qiaogao Huang
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.
{"title":"Wake characteristics at the fin tip streamwise cross-section of a manta robot","authors":"Tian Bao , Ya Zhang , 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":"2026-01-17","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}
Pub Date : 2026-01-17DOI: 10.1016/j.euromechflu.2026.204471
B. An , K.D. Chen , P.H. Song , Y.K. Guan , X. Hu
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.
{"title":"Numerical research on 2D wall-driven cavity flows: A review for Hopf bifurcation and steady vortical structures","authors":"B. An , K.D. Chen , P.H. Song , Y.K. Guan , 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":"2026-01-17","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}
The yarn in the pneumatic guiding tube has high fineness and considerable flexibility. As a result, it undergoes complex deformations under the airflow, making the fluid–structure interaction (FSI) between the yarn and airflow difficult to simulate. This study develops a weakly coupled numerical simulation framework to address this issue. The airflow and the fine yarn are modeled separately. The flow velocity is obtained using an upstream sampling method and applied to the yarn model. The yarn dynamics model is advanced using the implicit method. After updating the yarn position, the flow field is updated via force projection, thereby realizing a two-way FSI simulation. The kinematic and dynamic characteristics of yarn under pneumatic guiding tube control are systematically investigated through the framework. In yarn conveying process, the yarn quality flow stability and distribution concentration are found to increase first and then decrease with the increase of the input flow velocity. For the yarn tensioning process, the tension and vibration of the yarn continuously increase as the input velocity rises. The simulation framework is validated through experimental comparisons. Based on the simulation results and experimental data, the allowable ranges and optimal intervals of input velocity under different operating conditions are determined.
{"title":"Yarn dynamics in a pneumatic guiding tube: Numerical simulation and experimental validation","authors":"Tianbo Liu, Qitao Huang, Yuliang Yan, Tianyi Wang, Jiahui Wang, Hongguang Xu","doi":"10.1016/j.euromechflu.2026.204464","DOIUrl":"10.1016/j.euromechflu.2026.204464","url":null,"abstract":"<div><div>The yarn in the pneumatic guiding tube has high fineness and considerable flexibility. As a result, it undergoes complex deformations under the airflow, making the fluid–structure interaction (FSI) between the yarn and airflow difficult to simulate. This study develops a weakly coupled numerical simulation framework to address this issue. The airflow and the fine yarn are modeled separately. The flow velocity is obtained using an upstream sampling method and applied to the yarn model. The yarn dynamics model is advanced using the implicit method. After updating the yarn position, the flow field is updated via force projection, thereby realizing a two-way FSI simulation. The kinematic and dynamic characteristics of yarn under pneumatic guiding tube control are systematically investigated through the framework. In yarn conveying process, the yarn quality flow stability and distribution concentration are found to increase first and then decrease with the increase of the input flow velocity. For the yarn tensioning process, the tension and vibration of the yarn continuously increase as the input velocity rises. The simulation framework is validated through experimental comparisons. Based on the simulation results and experimental data, the allowable ranges and optimal intervals of input velocity under different operating conditions are determined.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"118 ","pages":"Article 204464"},"PeriodicalIF":2.5,"publicationDate":"2026-01-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146074605","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}
Pub Date : 2026-01-14DOI: 10.1016/j.euromechflu.2026.204470
Zafar Hayat Khan , Waqar Ahmed Khan , Alexander Trounev , Li-Bin Liu
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 () using the unsteady incompressible Navier–Stokes equations solved through the finite element method (FEM) implemented in Wolfram Mathematica. 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 ( at ), slightly lower than that of a canonical circular cylinder (). In contrast, the asymmetric Siegel disk fractal generates a strong negative lift ( at ) and achieves further drag reduction () at higher Reynolds numbers, accompanied by intensified wake unsteadiness and an increased pressure loss ( at ). A distinct transitional regime occurs between and , followed by partial recovery of steady flow for the Siegel disk fractal at . 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.
{"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 , Waqar Ahmed Khan , Alexander Trounev , 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":"2026-01-14","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}
Pub Date : 2026-01-13DOI: 10.1016/j.euromechflu.2026.204466
D. Matuz , F. Méndez , J. Arcos , O. Bautista , R. Baños
In this study, we examine the oscillatory squeeze flow of a viscoelastic fluid confined between two hydrophobic spheres of differing radii. The fluid flow is generated by the harmonic motion of an upper sphere, while the lower sphere remains stationary. We have considered that the gap between the spheres is much smaller than their radii and that the oscillation amplitude of the moving sphere is small compared to this gap. Under these conditions, the curved surfaces can be approximated by quadratic functions of the radial coordinate . A dynamic slip law is used to model slippage at the fluid–solid interface, which incorporates interfacial memory effects through the slip-relaxation time, together with the slip-yield Spikes–Granick condition, in which interfacial slippage arises when the fluid shear stress exceeds a critical value; otherwise, a non-slip region persists. Given the dominance of viscous over inertial effects, the convective terms in the momentum equation were neglected, and the analysis was carried out in a strictly periodic regimen. An analytical solution of the governing equations is derived, where the following parameters control the phenomenon: the Deborah number , the Womersley number , the Navier slip length , the slip relaxation number and the critical shear stress at the fluid–solid interface . Our findings indicate that, relative to flat surfaces, when curved surfaces are assumed, the zone of the non-slip region decreases. Additionally, incorporating viscoelastic fluids results in a diminished compression force, and lower mechanical power is consumed by implementing hydrophobic surfaces, high oscillation frequencies, and viscoelastic fluids.
{"title":"Influence of slip-yield stress model on the oscillatory squeeze flow of a viscoelastic fluid confined between two spheres","authors":"D. Matuz , F. Méndez , J. Arcos , O. Bautista , R. Baños","doi":"10.1016/j.euromechflu.2026.204466","DOIUrl":"10.1016/j.euromechflu.2026.204466","url":null,"abstract":"<div><div>In this study, we examine the oscillatory squeeze flow of a viscoelastic fluid confined between two hydrophobic spheres of differing radii. The fluid flow is generated by the harmonic motion of an upper sphere, while the lower sphere remains stationary. We have considered that the gap between the spheres is much smaller than their radii and that the oscillation amplitude of the moving sphere is small compared to this gap. Under these conditions, the curved surfaces can be approximated by quadratic functions of the radial coordinate <span><math><mi>r</mi></math></span>. A dynamic slip law is used to model slippage at the fluid–solid interface, which incorporates interfacial memory effects through the slip-relaxation time, together with the slip-yield Spikes–Granick condition, in which interfacial slippage arises when the fluid shear stress exceeds a critical value; otherwise, a non-slip region persists. Given the dominance of viscous over inertial effects, the convective terms in the momentum equation were neglected, and the analysis was carried out in a strictly periodic regimen. An analytical solution of the governing equations is derived, where the following parameters control the phenomenon: the Deborah number <span><math><mtext>De</mtext></math></span>, the Womersley number <span><math><mi>α</mi></math></span>, the Navier slip length <span><math><mover><mrow><mi>λ</mi></mrow><mrow><mo>̃</mo></mrow></mover></math></span>, the slip relaxation number <span><math><msub><mrow><mtext>De</mtext></mrow><mrow><mi>s</mi></mrow></msub></math></span> and the critical shear stress at the fluid–solid interface <span><math><msub><mrow><mover><mrow><mi>τ</mi></mrow><mrow><mo>̃</mo></mrow></mover></mrow><mrow><mi>c</mi></mrow></msub></math></span>. Our findings indicate that, relative to flat surfaces, when curved surfaces are assumed, the zone of the non-slip region decreases. Additionally, incorporating viscoelastic fluids results in a diminished compression force, and lower mechanical power is consumed by implementing hydrophobic surfaces, high oscillation frequencies, and viscoelastic fluids.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"118 ","pages":"Article 204466"},"PeriodicalIF":2.5,"publicationDate":"2026-01-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145974617","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}
Pub Date : 2026-01-08DOI: 10.1016/j.euromechflu.2026.204463
Xishuai Yu, Jianxi Zhou, Yong Li
This study investigates the effectiveness of leading-edge serrations as a passive noise control strategy for tandem airfoils across different angles of attack. Far-field noise measurements indicate that applying leading-edge serrations to the front airfoil significantly reduces wake turbulence interaction noise at 5° and 10° angles of attack; however, the reduction effect weakens as the angle of attack increases. At an angle of attack of 17°, the leading-edge serrations no longer reduce the peak wake turbulence interaction noise. Furthermore, neither the application of leading-edge serrations nor changes in the airfoil angle of attack affect the noise directivity. Flow field analyses based on Particle Image Velocimetry (PIV) reveal that the serrated leading edge markedly attenuates turbulence and vortex shedding in the wake of the front airfoil. Notably, as the angle of attack increases, the influence of vortex shedding and vortex–solid interference between the front and rear airfoils on the overall noise decreases. The intensity of the front airfoil wake turbulence and the extent of its interaction with the rear airfoil are identified as the dominant factors governing the interaction noise in tandem airfoils. Therefore, the application of leading-edge serrations in tandem airfoils is recommended only for low angles of attack. These findings may offer practical guidance for noise reduction in airfoil arrays of rotating machinery, such as guide vane rows, fan blade rows, and turbine blade rows.
{"title":"Influence of front airfoil leading-edge serrations on turbulence interaction noise characteristics of tandem airfoils at different angles of attack","authors":"Xishuai Yu, Jianxi Zhou, Yong Li","doi":"10.1016/j.euromechflu.2026.204463","DOIUrl":"10.1016/j.euromechflu.2026.204463","url":null,"abstract":"<div><div>This study investigates the effectiveness of leading-edge serrations as a passive noise control strategy for tandem airfoils across different angles of attack. Far-field noise measurements indicate that applying leading-edge serrations to the front airfoil significantly reduces wake turbulence interaction noise at 5° and 10° angles of attack; however, the reduction effect weakens as the angle of attack increases. At an angle of attack of 17°, the leading-edge serrations no longer reduce the peak wake turbulence interaction noise. Furthermore, neither the application of leading-edge serrations nor changes in the airfoil angle of attack affect the noise directivity. Flow field analyses based on Particle Image Velocimetry (PIV) reveal that the serrated leading edge markedly attenuates turbulence and vortex shedding in the wake of the front airfoil. Notably, as the angle of attack increases, the influence of vortex shedding and vortex–solid interference between the front and rear airfoils on the overall noise decreases. The intensity of the front airfoil wake turbulence and the extent of its interaction with the rear airfoil are identified as the dominant factors governing the interaction noise in tandem airfoils. Therefore, the application of leading-edge serrations in tandem airfoils is recommended only for low angles of attack. These findings may offer practical guidance for noise reduction in airfoil arrays of rotating machinery, such as guide vane rows, fan blade rows, and turbine blade rows.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"118 ","pages":"Article 204463"},"PeriodicalIF":2.5,"publicationDate":"2026-01-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145974619","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}
Pub Date : 2026-01-08DOI: 10.1016/j.euromechflu.2026.204462
Prathamesh Banda, Mayank Verma , D.V.G. Prasad, Ashoke De
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.
本文研究了不同阵列几何形状下VAWT簇的气动性能。研究了垂直轴风力涡轮机（VAWTs）的交错v形集群，以评估紧凑风电场布局中的气动相互作用。配置使用六个UNH-RVAT参考涡轮机，在集群角度，流向间距和涡轮机计数的变化。采用改进的Xcompact3D求解器进行了高保真作动线大涡模拟（LES）。对六涡轮集群进行了分析，集群角度为20°，30°和45°，流向间距为2D和3D（两个或三个转子直径）。结果与减少的五涡轮集群进行了比较。簇角对尾迹重叠和功率捕获有很大影响。在窄角（20°）时，尾流屏蔽严重，下游输出降低，而广角（45°）可以改善尾流恢复，但会降低上游协同。中间角度（30°）通过平衡这些影响产生最高的整体阵列性能。增加的流向间距（3D vs 2D）显著提高了尾迹恢复，并显著提高了下游涡轮效率。将涡轮数量从6台减少到5台进一步减轻了尾迹损失，从而提高了平均功率系数和更均匀的流入。流场诊断（速度、涡度、动能亏损）证实了这些趋势。这些结果为设计提供了指导：优化簇角、间距和涡轮数量可以大大提高高密度VAWT阵列的效率和鲁棒性。
{"title":"High-fidelity actuator line large eddy simulations of multi-turbine VAWT clusters under varying geometric configurations","authors":"Prathamesh Banda, Mayank Verma , D.V.G. Prasad, 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":"2026-01-08","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}
Pub Date : 2026-01-07DOI: 10.1016/j.euromechflu.2025.204452
Yutaro Motoori, Hideki Murahata, Susumu Goto
We visualise the hierarchy of coherent vortices generated by a freely swimming dolphin, obtained from direct numerical simulations at a high Reynolds number. The visualisations are based on isosurfaces of the second invariant of the velocity gradient tensor evaluated from scale-decomposed velocity fields. We describe in detail the scale-decomposition procedure and the polygon-based visualisation, which enables the rendering of the data despite their large size. We also emphasise that visualising the hierarchy of coherent vortices clarifies the physical mechanism of dolphin propulsion, and more generally, provides physical insight into turbulence around swimming and flying organisms.
{"title":"Visualising coherent vortices generated by a swimming dolphin","authors":"Yutaro Motoori, Hideki Murahata, Susumu Goto","doi":"10.1016/j.euromechflu.2025.204452","DOIUrl":"10.1016/j.euromechflu.2025.204452","url":null,"abstract":"<div><div>We visualise the hierarchy of coherent vortices generated by a freely swimming dolphin, obtained from direct numerical simulations at a high Reynolds number. The visualisations are based on isosurfaces of the second invariant of the velocity gradient tensor evaluated from scale-decomposed velocity fields. We describe in detail the scale-decomposition procedure and the polygon-based visualisation, which enables the rendering of the data despite their large size. We also emphasise that visualising the hierarchy of coherent vortices clarifies the physical mechanism of dolphin propulsion, and more generally, provides physical insight into turbulence around swimming and flying organisms.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"118 ","pages":"Article 204452"},"PeriodicalIF":2.5,"publicationDate":"2026-01-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145974618","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}
Pub Date : 2026-01-02DOI: 10.1016/j.euromechflu.2025.204453
G. Antar , J. El Kuweiss , K. Schneider , C. Habchi , S. Benkadda
We experimentally investigate quasi-two-dimensional (Q2D) forced shallow flows in the presence of solid boundaries and analyze the deviation from the Kolmogorov–Kraichnan (KK) theory. Complex motion is generated using a thin electrolyte subject to electromagnetic forces, and we employ particle tracking velocimetry to resolve the flow properties down to the Kolmogorov scale. Although the velocity probability distribution function closely resembles a Gaussian, deviations from Gaussianity emerge for velocity increments as scales decrease. The second-order structure function supports the onset of local anisotropy at small scales. The sign of the third-order structure function indicates the dominance of the inverse cascade in energy transfer, and the cross-correlation between longitudinal and transverse directions proves to be significant at large scales. The breakdown of local isotropy is consistent with the effect of bottom friction, which primarily affects the longitudinal motion, while leaving the perpendicular direction unaffected. This local anisotropy propagates to larger scales via the inverse energy cascade, with nonlinear interactions eventually influencing the perpendicular direction.
{"title":"On the local anisotropy of quasi-two-dimensional forced shallow flow: An experimental study","authors":"G. Antar , J. El Kuweiss , K. Schneider , C. Habchi , S. Benkadda","doi":"10.1016/j.euromechflu.2025.204453","DOIUrl":"10.1016/j.euromechflu.2025.204453","url":null,"abstract":"<div><div>We experimentally investigate quasi-two-dimensional (Q2D) forced shallow flows in the presence of solid boundaries and analyze the deviation from the Kolmogorov–Kraichnan (KK) theory. Complex motion is generated using a thin electrolyte subject to electromagnetic forces, and we employ particle tracking velocimetry to resolve the flow properties down to the Kolmogorov scale. Although the velocity probability distribution function closely resembles a Gaussian, deviations from Gaussianity emerge for velocity increments as scales decrease. The second-order structure function supports the onset of local anisotropy at small scales. The sign of the third-order structure function indicates the dominance of the inverse cascade in energy transfer, and the cross-correlation between longitudinal and transverse directions proves to be significant at large scales. The breakdown of local isotropy is consistent with the effect of bottom friction, which primarily affects the longitudinal motion, while leaving the perpendicular direction unaffected. This local anisotropy propagates to larger scales <em>via</em> the inverse energy cascade, with nonlinear interactions eventually influencing the perpendicular direction.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"118 ","pages":"Article 204453"},"PeriodicalIF":2.5,"publicationDate":"2026-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145904126","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}
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