Pub Date : 2025-08-16DOI: 10.1016/j.euromechflu.2025.204347
Tao Wang, Hongyu Gao, Dahai Luo, Bingxiao Lu
This study explores the performance of barchan dune-shaped vortex generators (BDVGs) as a passive flow control device on a circular cylinder at a Reynolds number of 3900. Using large eddy simulations (LES), the flow field around the cylinder, with BDVGs mounted symmetrically on its upper and lower surfaces, is analyzed. Two geometric configurations of BDVGs—slender (type I) and stubby (type II)—are compared to assess their effects on drag and lift coefficients across varying installation heights. The results demonstrate that BDVGs effectively reduce both the drag coefficient and the amplitude of aerodynamic force fluctuations. Notably, type II BDVGs outperform type I, achieving a maximum drag reduction of 6.17 %. Furthermore, BDVGs decrease the maximum amplitude of lift coefficient oscillations to 35.37 % of that observed for a smooth cylinder. These findings underscore the potential of BDVGs as practical and efficient solutions for aerodynamic flow control.
{"title":"Large eddy simulation of a circular cylinder mounted with barchan dune-shaped vortex generators","authors":"Tao Wang, Hongyu Gao, Dahai Luo, Bingxiao Lu","doi":"10.1016/j.euromechflu.2025.204347","DOIUrl":"10.1016/j.euromechflu.2025.204347","url":null,"abstract":"<div><div>This study explores the performance of barchan dune-shaped vortex generators (BDVGs) as a passive flow control device on a circular cylinder at a Reynolds number of 3900. Using large eddy simulations (LES), the flow field around the cylinder, with BDVGs mounted symmetrically on its upper and lower surfaces, is analyzed. Two geometric configurations of BDVGs—slender (type I) and stubby (type II)—are compared to assess their effects on drag and lift coefficients across varying installation heights. The results demonstrate that BDVGs effectively reduce both the drag coefficient and the amplitude of aerodynamic force fluctuations. Notably, type II BDVGs outperform type I, achieving a maximum drag reduction of 6.17 %. Furthermore, BDVGs decrease the maximum amplitude of lift coefficient oscillations to 35.37 % of that observed for a smooth cylinder. These findings underscore the potential of BDVGs as practical and efficient solutions for aerodynamic flow control.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"114 ","pages":"Article 204347"},"PeriodicalIF":2.5,"publicationDate":"2025-08-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144858551","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 : 2025-08-14DOI: 10.1016/j.euromechflu.2025.204349
Giovanni B. Ferreri
Several practical applications require a big number of pipes to be calculated a great many times in a short time. In such cases, an explicit formula for determination of the friction factor of the Darcy-Weisbach formula is advisable for noticeably shortening the computation time, with respect to a trial-and-error solution of the Colebrook-White (C-W) formula. In the present paper, unlike previous studies, an explicit formula is obtained based on the result by Colebrook himself that the deviation, here named δ, between the reciprocals of the square roots of the actual friction factor and that relating to a fully turbulent flow in the same pipe is a function of the friction Reynolds number only, Re*. To this aim, a criterion for better estimating the limit Re* value up to which a transitional regime can occur is also given, a limit value that can differ very much from the usual value 70. The explicit formula was achieved by processing a dataset, consisting of a big number of dyads (Re*, δ) generated over a wide range of relative roughnesses and, for each of the latter, over the Re* range where a transitional regime can occur, the latter range reaching the “new” limits for transitional flow as assumed here. The simple formula gives acceptable accuracy for practical engineering purposes.
{"title":"Explicit approximation of the Colebrook-White formula based on the friction Reynolds number","authors":"Giovanni B. Ferreri","doi":"10.1016/j.euromechflu.2025.204349","DOIUrl":"10.1016/j.euromechflu.2025.204349","url":null,"abstract":"<div><div>Several practical applications require a big number of pipes to be calculated a great many times in a short time. In such cases, an explicit formula for determination of the friction factor of the Darcy-Weisbach formula is advisable for noticeably shortening the computation time, with respect to a trial-and-error solution of the Colebrook-White (C-W) formula. In the present paper, unlike previous studies, an explicit formula is obtained based on the result by Colebrook himself that the deviation, here named <em>δ</em>, between the reciprocals of the square roots of the actual friction factor and that relating to a fully turbulent flow in the same pipe is a function of the friction Reynolds number only, <em>Re</em>*. To this aim, a criterion for better estimating the limit <em>Re</em>* value up to which a transitional regime can occur is also given, a limit value that can differ very much from the usual value 70. The explicit formula was achieved by processing a dataset, consisting of a big number of dyads (<em>Re</em>*, <em>δ</em>) generated over a wide range of relative roughnesses and, for each of the latter, over the <em>Re</em>* range where a transitional regime can occur, the latter range reaching the “new” limits for transitional flow as assumed here. The simple formula gives acceptable accuracy for practical engineering purposes.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"114 ","pages":"Article 204349"},"PeriodicalIF":2.5,"publicationDate":"2025-08-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144885638","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 : 2025-08-14DOI: 10.1016/j.euromechflu.2025.204340
Ahmed Aboelezz , Wei-Chung Su , Mohammad Rezaee , Pedram Roghanchi
The resurgence of black lung disease among miners underscores the pressing need to enhance our understanding of respirable dust deposition mechanisms. This paper critically evaluates the widespread practice of simplifying bronchioles geometries in dust deposition studies, a method commonly employed but often without adequate consideration of its impact on particle–wall interactions and subsequent deposition calculations. Through the integration of experimental setups with computational simulations, this study investigates the behavior of respirable coal dust using Particle Image Velocimetry (PIV) and a specially designed dust wind tunnel equipped with both complex and simplified bronchioles models. Further, this research employs Computational Fluid Dynamics-Discrete Phase Model (CFD-DPM) simulations within ANSYS Fluent, incorporating these diverse models to assess the ramifications of geometrical simplification. A bronchioles wall observing model was introduced to enhance the simulation’s realism by more accurately representing the dynamic interactions between dust particles and bronchioles wall surfaces. The complex model showed about 1.5×higher dust deposition compared to the simplified model. This difference was partially attributed to its larger surface area, with a surface area ratio of approximately 1.92. A correction factor based on this ratio was proposed to enhance the predictive capability of simplified models. This approach not only sheds light on the significant influences of particle size and airway geometry on dust deposition but also challenges the reliability of simplified models in replicating these complex processes. This work contributes valuable insights into improving occupational health safety measures in mining and related industries, highlighting the need for careful consideration of model selection and its implications in environmental health research.
{"title":"Evaluating the effects of bronchioles simplification on respirable dust deposition: A combined experimental and CFD-DPM analysis approach","authors":"Ahmed Aboelezz , Wei-Chung Su , Mohammad Rezaee , Pedram Roghanchi","doi":"10.1016/j.euromechflu.2025.204340","DOIUrl":"10.1016/j.euromechflu.2025.204340","url":null,"abstract":"<div><div>The resurgence of black lung disease among miners underscores the pressing need to enhance our understanding of respirable dust deposition mechanisms. This paper critically evaluates the widespread practice of simplifying bronchioles geometries in dust deposition studies, a method commonly employed but often without adequate consideration of its impact on particle–wall interactions and subsequent deposition calculations. Through the integration of experimental setups with computational simulations, this study investigates the behavior of respirable coal dust using Particle Image Velocimetry (PIV) and a specially designed dust wind tunnel equipped with both complex and simplified bronchioles models. Further, this research employs Computational Fluid Dynamics-Discrete Phase Model (CFD-DPM) simulations within ANSYS Fluent, incorporating these diverse models to assess the ramifications of geometrical simplification. A bronchioles wall observing model was introduced to enhance the simulation’s realism by more accurately representing the dynamic interactions between dust particles and bronchioles wall surfaces. The complex model showed about 1.5×higher dust deposition compared to the simplified model. This difference was partially attributed to its larger surface area, with a surface area ratio of approximately 1.92. A correction factor based on this ratio was proposed to enhance the predictive capability of simplified models. This approach not only sheds light on the significant influences of particle size and airway geometry on dust deposition but also challenges the reliability of simplified models in replicating these complex processes. This work contributes valuable insights into improving occupational health safety measures in mining and related industries, highlighting the need for careful consideration of model selection and its implications in environmental health research.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"114 ","pages":"Article 204340"},"PeriodicalIF":2.5,"publicationDate":"2025-08-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144852745","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}
In this work, a further study on turbulence states and structures in horizontal and vertical channels for liquid lead with unstable stratification by buoyancy is carried out based on the latest published high-fidelity direct numerical simulation (DNS) database. The mixed flow in horizontal and vertical channel conditions at , , and , 0.25, 0.5, 1 are considered. The turbulence states of liquid lead with different buoyant effects are studied with Lumley triangle. The results indicate that different buoyant effects have a remarkable impact on turbulence states, in which the collapse of invariant trajectories in outer region suggests similarity. Large-scale organized motions and large-scale thermal structures are identified through instantaneous fields and quantitatively analyzed using one-dimensional premultiplied wavenumber spectra. The typical spanwise wavelengths of large-scale organized motions and large-scale thermal structures induced by buoyancy are approximately and , respectively, where is channel half-width. Detailed analyses with intuitive instantaneous fields and quantitative premultiplied wavenumber spectra are performed to investigate physical mechanisms in mixed channel flows with different buoyant effects for liquid lead. It is expected that this study would give insights into mean flow characteristics in mixed horizontal and vertical channel flows with unstable stratification for liquid lead.
{"title":"Mean flow characteristics in horizontal and vertical channels with unstable stratification by buoyancy for liquid lead","authors":"Xingguang Zhou , Dalin Zhang , Xinyu Li , Wentao Guo , Hongxing Yu , Wenxi Tian , Suizheng Qiu , Guanghui Su","doi":"10.1016/j.euromechflu.2025.204344","DOIUrl":"10.1016/j.euromechflu.2025.204344","url":null,"abstract":"<div><div>In this work, a further study on turbulence states and structures in horizontal and vertical channels for liquid lead with unstable stratification by buoyancy is carried out based on the latest published high-fidelity direct numerical simulation (DNS) database. The mixed flow in horizontal and vertical channel conditions at <span><math><mrow><mi>R</mi><msub><mrow><mi>e</mi></mrow><mrow><mi>τ</mi></mrow></msub><mo>=</mo><mn>150</mn></mrow></math></span>, <span><math><mrow><mi>P</mi><mi>r</mi><mo>=</mo><mn>0</mn><mo>.</mo><mn>025</mn></mrow></math></span>, and <span><math><mrow><mi>R</mi><mi>i</mi><mo>=</mo><mn>0</mn></mrow></math></span>, 0.25, 0.5, 1 are considered. The turbulence states of liquid lead with different buoyant effects are studied with Lumley triangle. The results indicate that different buoyant effects have a remarkable impact on turbulence states, in which the collapse of invariant trajectories in outer region suggests similarity. Large-scale organized motions and large-scale thermal structures are identified through instantaneous fields and quantitatively analyzed using one-dimensional premultiplied wavenumber spectra. The typical spanwise wavelengths of large-scale organized motions and large-scale thermal structures induced by buoyancy are approximately <span><math><mrow><mn>3</mn><mi>δ</mi></mrow></math></span> and <span><math><mrow><mn>2</mn><mi>π</mi><mi>δ</mi></mrow></math></span>, respectively, where <span><math><mi>δ</mi></math></span> is channel half-width. Detailed analyses with intuitive instantaneous fields and quantitative premultiplied wavenumber spectra are performed to investigate physical mechanisms in mixed channel flows with different buoyant effects for liquid lead. It is expected that this study would give insights into mean flow characteristics in mixed horizontal and vertical channel flows with unstable stratification for liquid lead.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"114 ","pages":"Article 204344"},"PeriodicalIF":2.5,"publicationDate":"2025-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144840715","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 : 2025-08-12DOI: 10.1016/j.euromechflu.2025.204346
Lu Liu , Zhihua Liu , Fantai Meng , Teng Wang , Tai Wang , Xinyu Dong
The research on droplet impact has always focused on rigid solid surfaces. In the past two decades, the study of droplet impact dynamics on soft substrates, represented by PDMS, has received increasing attention, mainly driven by the development of flexible electronic technology. However, research on the dynamics of droplet impact on liquid metal surfaces is still relatively insufficient. Compared with PDMS, liquid metals exhibit higher surface tension and lower viscoelasticity, indicating that their droplet impact dynamic behavior will be significantly different. This paper reports the experiments for ethanol droplets impact heated copper surfaces and liquid gallium surfaces, and the effects of the Weber number (We) and surface temperature were analyzed. The results show that the patterns of droplet impact heated copper surfaces and liquid gallium surfaces can be divided into reflection rebound, central jetting, rebound rotation, jetting with horizontal splashing, and breakup. The impact dynamics of droplets on copper surfaces mainly depend on We, while the impact dynamics of droplets on liquid gallium surfaces are related to both We and surface temperature. As the surface temperature of liquid gallium increases, droplet rotation and splashing are suppressed, and the droplet maximum spreading diameter Dmax decreases. A semi-empirical model for the maximum spreading diameter of droplets was established by introducing surface temperature correction to consider energy dissipation caused by surface deformation and viscoelasticity. The research results contribute to understanding the influences of surface deformation and viscoelasticity on droplet dynamics.
{"title":"Experimental study on impact dynamics of droplet on heated copper surfaces and liquid gallium surfaces","authors":"Lu Liu , Zhihua Liu , Fantai Meng , Teng Wang , Tai Wang , Xinyu Dong","doi":"10.1016/j.euromechflu.2025.204346","DOIUrl":"10.1016/j.euromechflu.2025.204346","url":null,"abstract":"<div><div>The research on droplet impact has always focused on rigid solid surfaces. In the past two decades, the study of droplet impact dynamics on soft substrates, represented by PDMS, has received increasing attention, mainly driven by the development of flexible electronic technology. However, research on the dynamics of droplet impact on liquid metal surfaces is still relatively insufficient. Compared with PDMS, liquid metals exhibit higher surface tension and lower viscoelasticity, indicating that their droplet impact dynamic behavior will be significantly different. This paper reports the experiments for ethanol droplets impact heated copper surfaces and liquid gallium surfaces, and the effects of the Weber number (<em>We</em>) and surface temperature were analyzed. The results show that the patterns of droplet impact heated copper surfaces and liquid gallium surfaces can be divided into reflection rebound, central jetting, rebound rotation, jetting with horizontal splashing, and breakup. The impact dynamics of droplets on copper surfaces mainly depend on <em>We</em>, while the impact dynamics of droplets on liquid gallium surfaces are related to both <em>We</em> and surface temperature. As the surface temperature of liquid gallium increases, droplet rotation and splashing are suppressed, and the droplet maximum spreading diameter <em>D</em><sub>max</sub> decreases. A semi-empirical model for the maximum spreading diameter of droplets was established by introducing surface temperature correction to consider energy dissipation caused by surface deformation and viscoelasticity. The research results contribute to understanding the influences of surface deformation and viscoelasticity on droplet dynamics.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"114 ","pages":"Article 204346"},"PeriodicalIF":2.5,"publicationDate":"2025-08-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144852746","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 : 2025-08-05DOI: 10.1016/j.euromechflu.2025.204337
Souhail Souai , Mahadul Islam , Samrat Hansda , Soraya Trabelsi , Sabrine Garrouri , Mamun Molla , Ezeddine Sediki
<div><div>Optimizing the geometry of cooling systems is vital for achieving the best thermal performance, ensuring energy efficiency, and supporting sustainability. This study introduces a novel approach by exploring the potential of a non-toxic hybrid nanofluid, an 80:20 water-propylene glycol blend combined with multi-walled carbon nanotubes (MWCNT) and iron oxide (Fe₃O₄) nanoparticles, within an innovative n-shaped heat exchanger. The research focuses on the impact of heat and mass sources on magnetohydrodynamic double-diffusive mixed convection (MHD-DDMC), emphasizing the intricate interactions between porous media, nanoparticle dynamics, cross-diffusion effects, and magnetic fields. Numerical simulations are conducted using the lattice Boltzmann method (LBM) to analyze the system's behavior. A sensitivity analysis, supported by Response Surface Methodology (RSM) and Analysis of Variance (ANOVA), quantifies the effects of various parameters on heat and mass transfer, establishing correlations for the average Nusselt number (<span><math><mrow><mover><mrow><mi>Nu</mi></mrow><mo>̅</mo></mover></mrow></math></span>) and Sherwood number (<span><math><mrow><mover><mrow><mi>Sh</mi></mrow><mo>̅</mo></mover></mrow></math></span>). Various dimensionless variables, including porosity (ε), nanoparticles volume fraction (ϕ), source size (a), Lewis number (Le), Richardson number (Ri), buoyancy ratio (Br), Darcy number (Da), Hartmann number (Ha), Soret number (S<sub>r</sub>), and Du<sub><em>f</em></sub>our number ( D<sub><em>f</em></sub>), were evaluated to understand their effect on fluid structure, heat, and mass transfer. The results show that as Le increases, <span><math><mrow><mover><mrow><mi>Nu</mi></mrow><mo>̅</mo></mover></mrow></math></span> decreases by 23 % at a= 0.1, while the average <span><math><mrow><mover><mrow><mi>Sh</mi></mrow><mo>̅</mo></mover></mrow></math></span> increases by 81 % at a= 0.3. Rising Ha from 0 to 90 causes <span><math><mrow><mover><mrow><mi>Nu</mi></mrow><mo>̅</mo></mover></mrow></math></span> to decrease by 58 %, and <span><math><mrow><mover><mrow><mi>Sh</mi></mrow><mo>̅</mo></mover></mrow></math></span> to decrease by 58 % at a= 0.3. Furthermore, reducing Da from 10⁻¹ to 10⁻⁵ results in the highest increase in <span><math><mrow><mover><mrow><mi>Nu</mi></mrow><mo>̅</mo></mover></mrow></math></span> by 56 %, and the largest rise in <span><math><mrow><mover><mrow><mi>Sh</mi></mrow><mo>̅</mo></mover></mrow></math></span> by 67 % at a= 0.3. Sensitivity analysis revealed that the ϕ, D<sub><em>f</em></sub>, and parameters Br, S<sub><em>r</em></sub>, and Ri are among the most influential parameters, with their effects on heat and mass transfer being statistically significant according to ANOVA results. At high concentrations, ϕ enhances heat transfer, while D<sub><em>f</em></sub> significantly improves mass transfer. Additionally, <span><math><mi>a</mi></math></span>, Br, S<sub><em>r</em></sub>, and ϕ positively contribute to b
{"title":"Assessment of heat and mass transfer in a porous n-shaped heat exchanger using hybrid nanofluid under cross-diffusion and magnetic effects","authors":"Souhail Souai , Mahadul Islam , Samrat Hansda , Soraya Trabelsi , Sabrine Garrouri , Mamun Molla , Ezeddine Sediki","doi":"10.1016/j.euromechflu.2025.204337","DOIUrl":"10.1016/j.euromechflu.2025.204337","url":null,"abstract":"<div><div>Optimizing the geometry of cooling systems is vital for achieving the best thermal performance, ensuring energy efficiency, and supporting sustainability. This study introduces a novel approach by exploring the potential of a non-toxic hybrid nanofluid, an 80:20 water-propylene glycol blend combined with multi-walled carbon nanotubes (MWCNT) and iron oxide (Fe₃O₄) nanoparticles, within an innovative n-shaped heat exchanger. The research focuses on the impact of heat and mass sources on magnetohydrodynamic double-diffusive mixed convection (MHD-DDMC), emphasizing the intricate interactions between porous media, nanoparticle dynamics, cross-diffusion effects, and magnetic fields. Numerical simulations are conducted using the lattice Boltzmann method (LBM) to analyze the system's behavior. A sensitivity analysis, supported by Response Surface Methodology (RSM) and Analysis of Variance (ANOVA), quantifies the effects of various parameters on heat and mass transfer, establishing correlations for the average Nusselt number (<span><math><mrow><mover><mrow><mi>Nu</mi></mrow><mo>̅</mo></mover></mrow></math></span>) and Sherwood number (<span><math><mrow><mover><mrow><mi>Sh</mi></mrow><mo>̅</mo></mover></mrow></math></span>). Various dimensionless variables, including porosity (ε), nanoparticles volume fraction (ϕ), source size (a), Lewis number (Le), Richardson number (Ri), buoyancy ratio (Br), Darcy number (Da), Hartmann number (Ha), Soret number (S<sub>r</sub>), and Du<sub><em>f</em></sub>our number ( D<sub><em>f</em></sub>), were evaluated to understand their effect on fluid structure, heat, and mass transfer. The results show that as Le increases, <span><math><mrow><mover><mrow><mi>Nu</mi></mrow><mo>̅</mo></mover></mrow></math></span> decreases by 23 % at a= 0.1, while the average <span><math><mrow><mover><mrow><mi>Sh</mi></mrow><mo>̅</mo></mover></mrow></math></span> increases by 81 % at a= 0.3. Rising Ha from 0 to 90 causes <span><math><mrow><mover><mrow><mi>Nu</mi></mrow><mo>̅</mo></mover></mrow></math></span> to decrease by 58 %, and <span><math><mrow><mover><mrow><mi>Sh</mi></mrow><mo>̅</mo></mover></mrow></math></span> to decrease by 58 % at a= 0.3. Furthermore, reducing Da from 10⁻¹ to 10⁻⁵ results in the highest increase in <span><math><mrow><mover><mrow><mi>Nu</mi></mrow><mo>̅</mo></mover></mrow></math></span> by 56 %, and the largest rise in <span><math><mrow><mover><mrow><mi>Sh</mi></mrow><mo>̅</mo></mover></mrow></math></span> by 67 % at a= 0.3. Sensitivity analysis revealed that the ϕ, D<sub><em>f</em></sub>, and parameters Br, S<sub><em>r</em></sub>, and Ri are among the most influential parameters, with their effects on heat and mass transfer being statistically significant according to ANOVA results. At high concentrations, ϕ enhances heat transfer, while D<sub><em>f</em></sub> significantly improves mass transfer. Additionally, <span><math><mi>a</mi></math></span>, Br, S<sub><em>r</em></sub>, and ϕ positively contribute to b","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"114 ","pages":"Article 204337"},"PeriodicalIF":2.5,"publicationDate":"2025-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144772120","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 : 2025-08-05DOI: 10.1016/j.euromechflu.2025.204335
G.L. Huang, A. Wang, X. Chen, G.H. Tu, J.Q. Chen
An investigation of effects of the localized steady uniform blowing (LSUB) on stationary Görtler vortices in a Mach 6.5 flow over a concave wall was carried out by solving two dimensional spatial eigenvalue problem (BiGlobal) and plane-marching parabolized stability equations (PSE3D) with help of direct numerical simulations (DNS). In the simulations, Görtler vortices are excited with spanwise wavelengths of 3 mm (1.5, is the thickness of boundary layer at = 80 mm where the concave wall starts). No-slip and adiabatic conditions are prescribed at the wall. The flow visualization reveals prominent sinuous perturbations in the transition process. When the LSUB is applied to the wall, the boundary layer becomes thicker. With the increase in the amplitude of the LSUB within an appropriate range, Görtler streaks keep more regular and do not break down even at the end of the model when the amplitude of the LSUB is 0.01 of the free-stream velocity. Subsequent stability analyses based on BiGlobal and PSE3D confirm that sinuous secondary instability modes are the most unstable, responsible for the breakdown of Görtler vortices, and the growth rates of the dominant sinuous mode decrease significantly with increasing the amplitude of the LSUB. Further analysis indicates that the LSUB remarkably delays the growth of Görtler vortices, thus reducing the spanwise gradient of the streamwise velocity, which results in the decreases of energy production of the spanwise velocity shear. Therefore, the sinuous secondary instability is stabilized, leading to the delay of boundary layer transition. Our work suggests an appealing transition control strategy for high-speed flows dominated by Görtler vortices.
采用直接数值模拟（DNS）方法，通过求解二维空间特征值问题（bigglobal）和平面推进抛物稳定性方程（PSE3D），研究了6.5马赫凹壁面上局部定常均匀吹风（LSUB）对静止Görtler涡的影响。在模拟中，Görtler涡旋的激发波长为3 mm （1.5δ， δ为凹壁开始处x = 80 mm处的边界层厚度）。在壁处规定了防滑和绝热条件。流动显示显示了过渡过程中明显的弯曲扰动。当LSUB作用于壁面时，边界层变厚。在适当范围内，随着LSUB振幅的增大，Görtler条纹更加规整，即使在模型结束时，当LSUB振幅为自由流速度的0.01时，也不会击穿。随后基于bigglobal和PSE3D的稳定性分析证实，弯曲次不稳定模态是最不稳定的，导致Görtler涡旋的击破，并且随着LSUB振幅的增加，主导弯曲模态的增长率显著降低。进一步分析表明，LSUB显著地延缓了Görtler涡旋的生长，从而减小了向流速度的跨向梯度，导致向流速度切变的产能减小。因此，弯曲的二次失稳被稳定，导致边界层过渡的延迟。我们的工作提出了一种吸引人的过渡控制策略，用于Görtler涡旋主导的高速流动。
{"title":"Control of stationary Görtler vortices-induced high-speed boundary layer transition: Localized steady uniform blowing","authors":"G.L. Huang, A. Wang, X. Chen, G.H. Tu, J.Q. Chen","doi":"10.1016/j.euromechflu.2025.204335","DOIUrl":"10.1016/j.euromechflu.2025.204335","url":null,"abstract":"<div><div>An investigation of effects of the localized steady uniform blowing (LSUB) on stationary Görtler vortices in a Mach 6.5 flow over a concave wall was carried out by solving two dimensional spatial eigenvalue problem (BiGlobal) and plane-marching parabolized stability equations (PSE3D) with help of direct numerical simulations (DNS). In the simulations, Görtler vortices are excited with spanwise wavelengths of 3 mm (1.5<span><math><mi>δ</mi></math></span>, <span><math><mi>δ</mi></math></span> is the thickness of boundary layer at <span><math><mi>x</mi></math></span> = 80 mm where the concave wall starts). No-slip and adiabatic conditions are prescribed at the wall. The flow visualization reveals prominent sinuous perturbations in the transition process. When the LSUB is applied to the wall, the boundary layer becomes thicker. With the increase in the amplitude of the LSUB within an appropriate range, Görtler streaks keep more regular and do not break down even at the end of the model when the amplitude of the LSUB is 0.01 of the free-stream velocity. Subsequent stability analyses based on BiGlobal and PSE3D confirm that sinuous secondary instability modes are the most unstable, responsible for the breakdown of Görtler vortices, and the growth rates of the dominant sinuous mode decrease significantly with increasing the amplitude of the LSUB. Further analysis indicates that the LSUB remarkably delays the growth of Görtler vortices, thus reducing the spanwise gradient of the streamwise velocity, which results in the decreases of energy production of the spanwise velocity shear. Therefore, the sinuous secondary instability is stabilized, leading to the delay of boundary layer transition. Our work suggests an appealing transition control strategy for high-speed flows dominated by Görtler vortices.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"114 ","pages":"Article 204335"},"PeriodicalIF":2.5,"publicationDate":"2025-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144780838","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 : 2025-08-05DOI: 10.1016/j.euromechflu.2025.204341
Sichang Xu, Gary W. Rankin
Although various steady and unsteady working mechanisms underlying energy separation in Ranque–Hilsch vortex tubes have been investigated since the 1930s, a clear consensus has yet to be established. In the present research, unsteady energy separation mechanisms in a single-outlet vortex tube are investigated. The single vortex tube is modelled using both steady and unsteady Computational Fluid Dynamics (CFD) approaches. The unsteady CFD simulations are conducted using a Detached Eddy Simulation, and the steady simulations are performed with the Reynolds Stress Model. The experimental energy separation performance of a single-outlet vortex tube reported in the literature, with and without damping of the unsteady disturbances, is reproduced numerically. The explanation given in the original work, which describes energy separation as a result of changes in the time-averaged tangential velocity profile due to acoustic streaming, is not supported by the current numerical results. Therefore, a further investigation is made to determine other unsteady mechanisms occurring within the device. The inherent complexity of the transient three-dimensional flow field complicates the interpretation of fundamental flow structures and their associated unsteady dynamics. This is overcome by applying Spectral Proper Orthogonal Decomposition (SPOD) to the CFD dataset. Analysis of the dominant SPOD modes reveals two unsteady mechanisms within the flow field, including the radial transport and dissipation of vortical structures as well as the rotation of semi-coherent “blades” formed by Rossby vortices. An important finding of this study is that the combined effect of these mechanisms accounts for the energy separation observed in the single-outlet vortex tube.
{"title":"Investigation of the working mechanism and unsteady effects inside a single-outlet vortex tube by implementing unsteady computational fluid dynamics and spectral proper orthogonal decomposition","authors":"Sichang Xu, Gary W. Rankin","doi":"10.1016/j.euromechflu.2025.204341","DOIUrl":"10.1016/j.euromechflu.2025.204341","url":null,"abstract":"<div><div>Although various steady and unsteady working mechanisms underlying energy separation in Ranque–Hilsch vortex tubes have been investigated since the 1930s, a clear consensus has yet to be established. In the present research, unsteady energy separation mechanisms in a single-outlet vortex tube are investigated. The single vortex tube is modelled using both steady and unsteady Computational Fluid Dynamics (CFD) approaches. The unsteady CFD simulations are conducted using a Detached Eddy Simulation, and the steady simulations are performed with the Reynolds Stress Model. The experimental energy separation performance of a single-outlet vortex tube reported in the literature, with and without damping of the unsteady disturbances, is reproduced numerically. The explanation given in the original work, which describes energy separation as a result of changes in the time-averaged tangential velocity profile due to acoustic streaming, is not supported by the current numerical results. Therefore, a further investigation is made to determine other unsteady mechanisms occurring within the device. The inherent complexity of the transient three-dimensional flow field complicates the interpretation of fundamental flow structures and their associated unsteady dynamics. This is overcome by applying Spectral Proper Orthogonal Decomposition (SPOD) to the CFD dataset. Analysis of the dominant SPOD modes reveals two unsteady mechanisms within the flow field, including the radial transport and dissipation of vortical structures as well as the rotation of semi-coherent “blades” formed by Rossby vortices. An important finding of this study is that the combined effect of these mechanisms accounts for the energy separation observed in the single-outlet vortex tube.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"114 ","pages":"Article 204341"},"PeriodicalIF":2.5,"publicationDate":"2025-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144781366","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 : 2025-07-29DOI: 10.1016/j.euromechflu.2025.204329
Michael S.H. Boutilier, Rohit G.S. Ghode
Liquid transport through membrane nanopores is often modelled as creeping flow through a finite thickness orifice plate. Experiments and molecular simulations have revealed the importance of slip in such pores, where the diameter can be orders of magnitude smaller than the slip length for materials such as carbon nanotubes and graphene. Approximate hydrodynamic resistance models considering access resistance to the pore and fully developed slip flow within the pore are sometimes applied to estimate flow rates. While this approach is very accurate without slip, it can result in large errors for long slip lengths. Even with large slip lengths, flow development in the entry/exit regions contribute significant pressure drops that should be accounted for. In this paper, we extend an infinite series formulation for no-slip creeping flow through a finite thickness orifice plate to slip flow through the same geometry. We develop an algebraic system of equations for the series coefficients that can be efficiently computed to determine the velocity and pressure fields for the selected pore aspect ratio and slip length. Accurate volume flow rates can be quickly calculated, and are tabulated for convenience. We refine the approximate hydrodynamic resistance model for this flow to include losses in the entry region and obtain a fit for the volume flow rate accurate to within 2.5% for all slip lengths and pore aspect ratios.
{"title":"Infinite series formulation for slip flow through a finite thickness orifice plate","authors":"Michael S.H. Boutilier, Rohit G.S. Ghode","doi":"10.1016/j.euromechflu.2025.204329","DOIUrl":"10.1016/j.euromechflu.2025.204329","url":null,"abstract":"<div><div>Liquid transport through membrane nanopores is often modelled as creeping flow through a finite thickness orifice plate. Experiments and molecular simulations have revealed the importance of slip in such pores, where the diameter can be orders of magnitude smaller than the slip length for materials such as carbon nanotubes and graphene. Approximate hydrodynamic resistance models considering access resistance to the pore and fully developed slip flow within the pore are sometimes applied to estimate flow rates. While this approach is very accurate without slip, it can result in large errors for long slip lengths. Even with large slip lengths, flow development in the entry/exit regions contribute significant pressure drops that should be accounted for. In this paper, we extend an infinite series formulation for no-slip creeping flow through a finite thickness orifice plate to slip flow through the same geometry. We develop an algebraic system of equations for the series coefficients that can be efficiently computed to determine the velocity and pressure fields for the selected pore aspect ratio and slip length. Accurate volume flow rates can be quickly calculated, and are tabulated for convenience. We refine the approximate hydrodynamic resistance model for this flow to include losses in the entry region and obtain a fit for the volume flow rate accurate to within 2.5% for all slip lengths and pore aspect ratios.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"114 ","pages":"Article 204329"},"PeriodicalIF":2.5,"publicationDate":"2025-07-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144852743","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 : 2025-07-28DOI: 10.1016/j.euromechflu.2025.204330
Rupam Saha , B. Hema Sundar Raju
This article explores the impact of free-stream flow orientation on the dynamics of flow past a circular cylinder under superimposed thermal buoyancy subjected to isoflux condition. It emphasizes how thermal buoyancy regulates boundary layer separation across different flow angles, offering valuable insights for optimizing thermal management in mixed convection systems. The effect caused by the fluid flow and thermal dynamics is highlighted along with entropy generation around the cylinder for various Reynolds numbers (), Richardson numbers (), and free-stream angles (). A fourth-order accurate finite difference scheme with a stable pseudo-time iterative method is developed to address the non-linear governing continuity, momentum and energy equations. The key findings reveal that the flow configuration remains symmetric along aiding and opposing flow regimes; otherwise, it becomes completely asymmetric. The superimposed thermal buoyancy controls the wake formation, which is strongly dependent upon the thermal boundary condition and flow orientation. Critical Richardson number () for suppressing the vortex shedding is evaluated for various parameters, and inter-parametric dependence of the is also disclosed under isoflux boundary condition. The rate of heat transfer increases within aiding to cross flow regime, whereas the same decreases within cross to opposing flow regime. The relative contribution of heat transfer entropy to the overall entropy, characterized by Bejan number, reduces with increasing in aiding and cross flow regime, while it increases in opposing flow regime.
{"title":"Directional dependence of fluid flow on mixed convection across an isoflux cylinder with entropy generation","authors":"Rupam Saha , B. Hema Sundar Raju","doi":"10.1016/j.euromechflu.2025.204330","DOIUrl":"10.1016/j.euromechflu.2025.204330","url":null,"abstract":"<div><div>This article explores the impact of free-stream flow orientation on the dynamics of flow past a circular cylinder under superimposed thermal buoyancy subjected to isoflux condition. It emphasizes how thermal buoyancy regulates boundary layer separation across different flow angles, offering valuable insights for optimizing thermal management in mixed convection systems. The effect caused by the fluid flow and thermal dynamics is highlighted along with entropy generation around the cylinder for various Reynolds numbers (<span><math><mrow><mn>5</mn><mo>≤</mo><mi>R</mi><mi>e</mi><mo>≤</mo><mn>40</mn></mrow></math></span>), Richardson numbers (<span><math><mrow><mn>0</mn><mo>≤</mo><mi>R</mi><mi>i</mi><mo>≤</mo><mn>1</mn><mo>.</mo><mn>5</mn></mrow></math></span>), and free-stream angles (<span><math><mrow><msup><mrow><mn>0</mn></mrow><mrow><mo>∘</mo></mrow></msup><mo>≤</mo><mi>α</mi><mo>≤</mo><mn>18</mn><msup><mrow><mn>0</mn></mrow><mrow><mo>∘</mo></mrow></msup></mrow></math></span>). A fourth-order accurate finite difference scheme with a stable pseudo-time iterative method is developed to address the non-linear governing continuity, momentum and energy equations. The key findings reveal that the flow configuration remains symmetric along aiding and opposing flow regimes; otherwise, it becomes completely asymmetric. The superimposed thermal buoyancy controls the wake formation, which is strongly dependent upon the thermal boundary condition and flow orientation. Critical Richardson number (<span><math><mrow><mi>R</mi><msub><mrow><mi>i</mi></mrow><mrow><mi>c</mi><mi>r</mi></mrow></msub></mrow></math></span>) for suppressing the vortex shedding is evaluated for various parameters, and inter-parametric dependence of the <span><math><mrow><mi>R</mi><msub><mrow><mi>i</mi></mrow><mrow><mi>c</mi><mi>r</mi></mrow></msub></mrow></math></span> is also disclosed under isoflux boundary condition. The rate of heat transfer increases within aiding to cross flow regime, whereas the same decreases within cross to opposing flow regime. The relative contribution of heat transfer entropy to the overall entropy, characterized by Bejan number, reduces with increasing <span><math><mrow><mi>R</mi><mi>i</mi></mrow></math></span> in aiding and cross flow regime, while it increases in opposing flow regime.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"114 ","pages":"Article 204330"},"PeriodicalIF":2.5,"publicationDate":"2025-07-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144713452","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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