Pub Date : 2025-02-13DOI: 10.1016/j.euromechflu.2025.01.013
Ibrahim Mert Hakligor, Gokturk M. Ozkan, Huseyin Akilli
The flow structure in the wake of circular screen cylinders was investigated experimentally by dye visualization and high-image density Particle Image Velocimetry (PIV) technique in shallow water. The effect of permeability was analyzed for four permeability ratios across varying Reynolds numbers. Results showed that permeability significantly influences the wake flow dynamics. Jet-like flow structures and Kelvin-Helmholtz instabilities with pulsating behavior were observed at minimum permeability, i.e., β = 0.4. As permeability increases, these structures extend downstream (β = 0.5), weaken (β = 0.6), or completely disappear for β = 0.7. Velocity deficits were found to be highest at β = 0.4 and decreased with greater permeability values. Turbulent fluctuations are dominant along shear layers that diminish with increasing permeability. Two-point spatial correlations revealed strong vortical interactions for β ≤ 0.5 that diminish for β ≥ 0.6. These findings highlight the critical role of permeability in the wake characteristics of circular screen cylinders, providing insights for relevant engineering applications.
{"title":"Flow structures in the near wake of permeable circular cylinders in shallow water","authors":"Ibrahim Mert Hakligor, Gokturk M. Ozkan, Huseyin Akilli","doi":"10.1016/j.euromechflu.2025.01.013","DOIUrl":"10.1016/j.euromechflu.2025.01.013","url":null,"abstract":"<div><div>The flow structure in the wake of circular screen cylinders was investigated experimentally by dye visualization and high-image density Particle Image Velocimetry (PIV) technique in shallow water. The effect of permeability was analyzed for four permeability ratios across varying Reynolds numbers. Results showed that permeability significantly influences the wake flow dynamics. Jet-like flow structures and Kelvin-Helmholtz instabilities with pulsating behavior were observed at minimum permeability, i.e., <em>β</em> = 0.4. As permeability increases, these structures extend downstream (<em>β</em> = 0.5), weaken (<em>β</em> = 0.6), or completely disappear for <em>β</em> = 0.7. Velocity deficits were found to be highest at <em>β</em> = 0.4 and decreased with greater permeability values. Turbulent fluctuations are dominant along shear layers that diminish with increasing permeability. Two-point spatial correlations revealed strong vortical interactions for <em>β</em> ≤ 0.5 that diminish for <em>β</em> ≥ 0.6. These findings highlight the critical role of permeability in the wake characteristics of circular screen cylinders, providing insights for relevant engineering applications.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"111 ","pages":"Pages 295-307"},"PeriodicalIF":2.5,"publicationDate":"2025-02-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143396088","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 : 2025-02-11DOI: 10.1016/j.euromechflu.2025.02.003
Kangfu Sun , Siying Zhang , Nuo Shi , Shaoqing Peng , Jingguo Cao , Jiao Sun , Wenyi Chen
We present an experimental study of synthetic jet vortex rings flowing through a honeycomb. A free synthetic jet generated by piston-cylinder apparatus is used to make a vortex, obtaining turbulence at Taylor Reynolds number Reλ ∼ 294. We sketch a conceptual picture of the passive control of the flow field by honeycomb. By choosing a length-to-cell ratio Φ = 2.1, we clearly show how the honeycomb affects the evolution of vortical structure flowing through a honeycomb. The mechanism associated with vorticity cancellation is that the finger-type jets shaping downstream of the honeycomb will reorganize into a transmitted vortex ring in the downstream flow. We chose three length-to-cell ratios (Φ = 3.7, 6.3, and 12.5) with a constant length of honeycomb to examine the effect of their geometry on the flow characteristic. We find that honeycomb redistributes the flow field and enhances the uniformity of the flow field. In addition, the selection of the length-to-cell ratio of honeycomb should correspond to the given experimental conditions, because the turbulence reduction and isotropy are not mutually beneficial. The results of velocity triple-decomposition show that the honeycomb can effectively reduce the periodic and random velocity fluctuation, revealing the mechanism of a relaminarization.
{"title":"Experimental investigation of synthetic jet impingement upon a honeycomb","authors":"Kangfu Sun , Siying Zhang , Nuo Shi , Shaoqing Peng , Jingguo Cao , Jiao Sun , Wenyi Chen","doi":"10.1016/j.euromechflu.2025.02.003","DOIUrl":"10.1016/j.euromechflu.2025.02.003","url":null,"abstract":"<div><div>We present an experimental study of synthetic jet vortex rings flowing through a honeycomb. A free synthetic jet generated by piston-cylinder apparatus is used to make a vortex, obtaining turbulence at Taylor Reynolds number <em>Re</em><sub><em>λ</em></sub> ∼ 294. We sketch a conceptual picture of the passive control of the flow field by honeycomb. By choosing a length-to-cell ratio <em>Φ</em> = 2.1, we clearly show how the honeycomb affects the evolution of vortical structure flowing through a honeycomb. The mechanism associated with vorticity cancellation is that the finger-type jets shaping downstream of the honeycomb will reorganize into a transmitted vortex ring in the downstream flow. We chose three length-to-cell ratios (<em>Φ</em> = 3.7, 6.3, and 12.5) with a constant length of honeycomb to examine the effect of their geometry on the flow characteristic. We find that honeycomb redistributes the flow field and enhances the uniformity of the flow field. In addition, the selection of the length-to-cell ratio of honeycomb should correspond to the given experimental conditions, because the turbulence reduction and isotropy are not mutually beneficial. The results of velocity triple-decomposition show that the honeycomb can effectively reduce the periodic and random velocity fluctuation, revealing the mechanism of a relaminarization.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"111 ","pages":"Pages 319-333"},"PeriodicalIF":2.5,"publicationDate":"2025-02-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143403368","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 : 2025-02-07DOI: 10.1016/j.euromechflu.2025.01.012
N. Nouaime , B. Després , M.A. Puscas , C. Fiorini
We present a stability estimate for the sensitivity of the incompressible Navier–Stokes equations under uncertainty in model parameters such as viscosity and initial or boundary conditions. The approach employs the stochastic Galerkin method, wherein the solution is represented using a generalized polynomial chaos expansion. The governing equations are projected onto stochastic basis functions, resulting in an extended coupled equation system. These coupled equations are challenging to solve numerically. A decoupling method is proposed to simplify their numerical resolution, which, along with the stability estimates, represents one of this study’s most valuable and original aspects. Finally, we present the lid-driven cavity numerical test to evaluate the polynomial chaos method and compare the solutions with the numerical data published in the literature.
{"title":"Sensitivity analysis for incompressible Navier–Stokes equations with uncertain viscosity using polynomial chaos method","authors":"N. Nouaime , B. Després , M.A. Puscas , C. Fiorini","doi":"10.1016/j.euromechflu.2025.01.012","DOIUrl":"10.1016/j.euromechflu.2025.01.012","url":null,"abstract":"<div><div>We present a stability estimate for the sensitivity of the incompressible Navier–Stokes equations under uncertainty in model parameters such as viscosity and initial or boundary conditions. The approach employs the stochastic Galerkin method, wherein the solution is represented using a generalized polynomial chaos expansion. The governing equations are projected onto stochastic basis functions, resulting in an extended coupled equation system. These coupled equations are challenging to solve numerically. A decoupling method is proposed to simplify their numerical resolution, which, along with the stability estimates, represents one of this study’s most valuable and original aspects. Finally, we present the lid-driven cavity numerical test to evaluate the polynomial chaos method and compare the solutions with the numerical data published in the literature.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"111 ","pages":"Pages 308-318"},"PeriodicalIF":2.5,"publicationDate":"2025-02-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143396089","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 : 2025-02-04DOI: 10.1016/j.euromechflu.2025.01.010
Zhiqun Guo , Jianming Miao , Sen Liu , Zhenfeng Zhai
By modeling the unique segmented arc-shaped breakwater at the periphery of the shallow waters of Dubai’s Palm Island, this paper provides insights into the complex mechanisms of interaction between solitary waves and one cylinder surrounded by multi-segmented concentric arc-shaped outer wall. This study presents an analytical solution using the matched eigenfunction method. Matching conditions are used to determine the initially unknown potential coefficients, ensuring that boundary flux and velocity constraints are met. The numerical results show a high degree of agreement with previous studies. The study examines key factors influencing hydrodynamic loads and diffracted wave surfaces, including incident angle, radius ratio and segment spacing. The findings suggest that segmented triple arc facades with appropriate segmental spacing provide superior shielding effect compared to non-segmented arc facades and circular structures. Additionally, when the arc facade is permeable to water, segmentation has little impact on its shielding effect. The numerical findings offer valuable insights for the engineering design of segmented arc structures.
{"title":"Analytical solution for solitary wave diffraction around a cylinder surrounded by multi-segmented arc-shaped wall","authors":"Zhiqun Guo , Jianming Miao , Sen Liu , Zhenfeng Zhai","doi":"10.1016/j.euromechflu.2025.01.010","DOIUrl":"10.1016/j.euromechflu.2025.01.010","url":null,"abstract":"<div><div>By modeling the unique segmented arc-shaped breakwater at the periphery of the shallow waters of Dubai’s Palm Island, this paper provides insights into the complex mechanisms of interaction between solitary waves and one cylinder surrounded by multi-segmented concentric arc-shaped outer wall. This study presents an analytical solution using the matched eigenfunction method. Matching conditions are used to determine the initially unknown potential coefficients, ensuring that boundary flux and velocity constraints are met. The numerical results show a high degree of agreement with previous studies. The study examines key factors influencing hydrodynamic loads and diffracted wave surfaces, including incident angle, radius ratio and segment spacing. The findings suggest that segmented triple arc facades with appropriate segmental spacing provide superior shielding effect compared to non-segmented arc facades and circular structures. Additionally, when the arc facade is permeable to water, segmentation has little impact on its shielding effect. The numerical findings offer valuable insights for the engineering design of segmented arc structures.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"111 ","pages":"Pages 283-294"},"PeriodicalIF":2.5,"publicationDate":"2025-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143372938","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 : 2025-01-27DOI: 10.1016/j.euromechflu.2025.01.008
Keith Davey , Abdullah Al-Tarmoom , Hamed Sadeghi
A hydraulic jump is a sudden rapid transition from a fast to a slower moving flow that is readily observed in open channels. The phenomenon has been extensively investigated both theoretically and experimentally, and is influenced by turbulence, gravity, wall friction, and fluid viscosity. The behaviour of a jump changes under scaling, which limits experimental investigations performed at scale, making scaled models unrepresentative. This issue is addressed in this paper with the introduction of a new experimental approach involving more than one scaled model. A new theory for scaling has recently appeared in the open literature that systematically removes scale effects by means of alternative similitude rules not available to dimensional analysis. This main focus in this paper is on the rule known as the first-order finite-similitude rule, involving two scaled experiments. The question addressed in the paper is whether it is possible, by means of additional scaled experiments, to capture more accurately hydraulic-jump behaviour. Both theoretical and experimentally-validated results are examined from the literature to support the contention that an additional scaled experiment provides significantly improved outcomes.
{"title":"A two-experiment approach to hydraulic jump scaling","authors":"Keith Davey , Abdullah Al-Tarmoom , Hamed Sadeghi","doi":"10.1016/j.euromechflu.2025.01.008","DOIUrl":"10.1016/j.euromechflu.2025.01.008","url":null,"abstract":"<div><div>A hydraulic jump is a sudden rapid transition from a fast to a slower moving flow that is readily observed in open channels. The phenomenon has been extensively investigated both theoretically and experimentally, and is influenced by turbulence, gravity, wall friction, and fluid viscosity. The behaviour of a jump changes under scaling, which limits experimental investigations performed at scale, making scaled models unrepresentative. This issue is addressed in this paper with the introduction of a new experimental approach involving more than one scaled model. A new theory for scaling has recently appeared in the open literature that systematically removes scale effects by means of alternative similitude rules not available to dimensional analysis. This main focus in this paper is on the rule known as the <em>first-order finite-similitude</em> rule, involving two scaled experiments. The question addressed in the paper is whether it is possible, by means of additional scaled experiments, to capture more accurately hydraulic-jump behaviour. Both theoretical and experimentally-validated results are examined from the literature to support the contention that an additional scaled experiment provides significantly improved outcomes.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"111 ","pages":"Pages 215-228"},"PeriodicalIF":2.5,"publicationDate":"2025-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143093479","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-01-27DOI: 10.1016/j.euromechflu.2025.01.011
Qingpeng Chen , Tan Cheng , Jiachen Yu , Feixiang Tang , Wei Wang , Guoqing Zhang , Fang Dong , Sheng Liu
Spatter particles are a major cause of part defects during laser powder bed fusion (LPBF). Filling the working chamber with an inert gas prevents oxidation of the part and simultaneously removes spatter particles. The flow of inert gas in the working chamber influences the spatter-particle trajectory. This study develops a new wind-duct circulation system design based on inert-gas flow characteristics. The inert gas flow characteristics in the chamber were investigated using a coupled computational fluid dynamics and discrete phase model. The Coanda effect influence on the wind field uniformity and motion trajectories of spatter particles in different regions of the LPBF chamber was analyzed. A Bernoulli-effect three-wind duct structure was designed to attenuate the Coanda effect, and the effects of nine sets of wind speed combinations were investigated. The results demonstrate that the newly designed three-wind duct structure effectively reduces the Coanda effect of the flow field inside the working chamber. Wind speed requirements in each functional area are ensured and the removal efficiency of spatter particles is enhanced (79–96 %). This solution addresses a critical issue found in existing commercial LPBF equipment, providing a reliable reference for the subsequent optimization and design of duct circulation systems.
{"title":"Simulation analysis of flow field optimization for powder bed surface integrity and spatter particle removal","authors":"Qingpeng Chen , Tan Cheng , Jiachen Yu , Feixiang Tang , Wei Wang , Guoqing Zhang , Fang Dong , Sheng Liu","doi":"10.1016/j.euromechflu.2025.01.011","DOIUrl":"10.1016/j.euromechflu.2025.01.011","url":null,"abstract":"<div><div>Spatter particles are a major cause of part defects during laser powder bed fusion (LPBF). Filling the working chamber with an inert gas prevents oxidation of the part and simultaneously removes spatter particles. The flow of inert gas in the working chamber influences the spatter-particle trajectory. This study develops a new wind-duct circulation system design based on inert-gas flow characteristics. The inert gas flow characteristics in the chamber were investigated using a coupled computational fluid dynamics and discrete phase model. The Coanda effect influence on the wind field uniformity and motion trajectories of spatter particles in different regions of the LPBF chamber was analyzed. A Bernoulli-effect three-wind duct structure was designed to attenuate the Coanda effect, and the effects of nine sets of wind speed combinations were investigated. The results demonstrate that the newly designed three-wind duct structure effectively reduces the Coanda effect of the flow field inside the working chamber. Wind speed requirements in each functional area are ensured and the removal efficiency of spatter particles is enhanced (79–96 %). This solution addresses a critical issue found in existing commercial LPBF equipment, providing a reliable reference for the subsequent optimization and design of duct circulation systems.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"111 ","pages":"Pages 266-282"},"PeriodicalIF":2.5,"publicationDate":"2025-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143093476","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 : 2025-01-27DOI: 10.1016/j.euromechflu.2025.01.005
P.M. Jordan
The propagation of finite-amplitude acoustic wave-forms in thermoviscous gases, assumed to admit constant transport coefficients, under two newly-introduced third order, bi-directional, equations of motion is investigated. Along with analyzing both under the traveling wave assumption, the present study also compares the wave-profiles exhibited by these new models, the simplest of which follows from Diaz et al. (2018), with those of their established counterparts. Connections between equations that comprise this now expanded collection of six acoustic models are highlighted, and the degree of approximation required to derive each from the acoustic Navier–Stokes–Fourier system is indicated via a hierarchical chart. It is also shown that the long-established model with the fewest approximations and the newer, more heavily approximated, Diaz, et al. model yield the same Taylor shock traveling wave profile.
{"title":"Updating our perspective on the bi-directional equations of dissipative, finite-amplitude acoustics theory: From Blackstock (1963) to Diaz–Solovchuk–Sheu (2018)","authors":"P.M. Jordan","doi":"10.1016/j.euromechflu.2025.01.005","DOIUrl":"10.1016/j.euromechflu.2025.01.005","url":null,"abstract":"<div><div>The propagation of finite-amplitude acoustic wave-forms in thermoviscous gases, assumed to admit constant transport coefficients, under two newly-introduced third order, bi-directional, equations of motion is investigated. Along with analyzing both under the traveling wave assumption, the present study also compares the wave-profiles exhibited by these new models, the simplest of which follows from Diaz et al. (2018), with those of their established counterparts. Connections between equations that comprise this now expanded collection of six acoustic models are highlighted, and the degree of approximation required to derive each from the acoustic Navier–Stokes–Fourier system is indicated via a hierarchical chart. It is also shown that the long-established model with the fewest approximations and the newer, more heavily approximated, Diaz, et al. model yield the <em>same</em> Taylor shock traveling wave profile.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"111 ","pages":"Pages 244-249"},"PeriodicalIF":2.5,"publicationDate":"2025-01-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143093477","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 : 2025-01-26DOI: 10.1016/j.euromechflu.2025.01.009
Neha Jain, Gaurav Sharma
The linear stability of gravity-driven flow of surfactant-laden liquid film over a rod is examined in creeping flow limit in presence of an applied shear stress at gas–liquid (GL) interface. This flow system admits two instability modes: (i) a surface-tension driven Rayleigh-Plateau (RP) mode, and (ii) a surface-tension gradient driven surfactant mode. In absence of imposed shear stress, the surfactant completely suppresses the RP instability when Marangoni number (Ma), increases above a critical value. On further increase of Ma to high enough values, the surfactant mode becomes unstable, and as a result, a gap in terms of Ma exists where the film flow remains stable. The present work shows that these stability characteristics are dramatically modified in presence of imposed shear stress. When shear stress acts in a direction to assist gravity-driven flow (i.e. positive stress), it has a stabilizing effect on RP mode in addition to the stabilizing effect of surfactant. In contrast, the positive applied shear destabilizes the surfactant mode when shear stress exceeds above a critical value. Below this critical stress value, it is still possible to obtain stable film flow for a range of Marangoni number values. However, above this critical value, the shear stress induced surfactant mode instability engulf whole region from low wave number to finite wave number perturbations for any value of Ma. For negative values of imposed shear (i.e. when shear stress acts opposite to gravity-driven flow direction), the effect of shear stress on RP mode is destabilizing (stabilizing) when the magnitude of applied stress is lower (higher) than a threshold value. On the other hand, the effect of applied negative shear is found to be exactly opposite for surfactant mode. The overall analysis of results for negative shear shows that it is not possible to obtain stable flows when magnitude of shear stress is above a certain value in a similar manner as shown for positive applied stress. It was also observed that the finite wave number perturbations become important for a wide range of parameters for shear stress induced destabilization of film flow configuration. This was not the case in absence of applied stress in which case the dominant perturbations were always long wavelength perturbations.
{"title":"Effect of imposed shear stress on the stability of surfactant-laden liquid film flow over a rod","authors":"Neha Jain, Gaurav Sharma","doi":"10.1016/j.euromechflu.2025.01.009","DOIUrl":"10.1016/j.euromechflu.2025.01.009","url":null,"abstract":"<div><div>The linear stability of gravity-driven flow of surfactant-laden liquid film over a rod is examined in creeping flow limit in presence of an applied shear stress at gas–liquid (GL) interface. This flow system admits two instability modes: (i) a surface-tension driven Rayleigh-Plateau (RP) mode, and (ii) a surface-tension gradient driven surfactant mode. In absence of imposed shear stress, the surfactant completely suppresses the RP instability when Marangoni number (Ma), increases above a critical value. On further increase of Ma to high enough values, the surfactant mode becomes unstable, and as a result, a gap in terms of Ma exists where the film flow remains stable. The present work shows that these stability characteristics are dramatically modified in presence of imposed shear stress. When shear stress acts in a direction to assist gravity-driven flow (i.e. positive stress), it has a stabilizing effect on RP mode in addition to the stabilizing effect of surfactant. In contrast, the positive applied shear destabilizes the surfactant mode when shear stress exceeds above a critical value. Below this critical stress value, it is still possible to obtain stable film flow for a range of Marangoni number values. However, above this critical value, the shear stress induced surfactant mode instability engulf whole region from low wave number to finite wave number perturbations for any value of Ma. For negative values of imposed shear (i.e. when shear stress acts opposite to gravity-driven flow direction), the effect of shear stress on RP mode is destabilizing (stabilizing) when the magnitude of applied stress is lower (higher) than a threshold value. On the other hand, the effect of applied negative shear is found to be exactly opposite for surfactant mode. The overall analysis of results for negative shear shows that it is not possible to obtain stable flows when magnitude of shear stress is above a certain value in a similar manner as shown for positive applied stress. It was also observed that the finite wave number perturbations become important for a wide range of parameters for shear stress induced destabilization of film flow configuration. This was not the case in absence of applied stress in which case the dominant perturbations were always long wavelength perturbations.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"111 ","pages":"Pages 229-243"},"PeriodicalIF":2.5,"publicationDate":"2025-01-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143093478","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 : 2025-01-20DOI: 10.1016/j.euromechflu.2025.01.004
N.K. Ranjit , G.C. Shit
In this paper, we examine the impact of joule heating and entropy generation on a time-periodic electroosmotic flow of viscoelastic fluids in a slowly varying microchannel under the influence of a magnetic field. We consider the Jeffrey fluid model, which describes the linear viscoelastic fluid, and an effort is made to obtain the analytical solutions, considering velocity and thermal slip conditions at the fluid–solid interface. The study reveals that the relaxation and retardation times in the Jeffrey fluid have a significant effect on the axial velocity and temperature distribution within the microchannel. Further, we observed that the Joule heating contributes to enhanced thermal response in both temperature distribution and Nusselt number, leading to increased entropy generation. The Bejan number profiles enhance with an increase in the Joule heating parameter due to the conversion of electrical energy into thermal energy. The velocity slip enhances the rate of heat transfer and entropy generation, while these quantities decrease with the thermal slip. The present study on AC electroosmosis and electrothermal flow shows significant promise as a fluid-driven technique in microfluidics for future endeavors.
{"title":"Joule heating and entropy generation on AC electroosmotic flow of Jeffrey fluid in a slowly varying micro-channel","authors":"N.K. Ranjit , G.C. Shit","doi":"10.1016/j.euromechflu.2025.01.004","DOIUrl":"10.1016/j.euromechflu.2025.01.004","url":null,"abstract":"<div><div>In this paper, we examine the impact of joule heating and entropy generation on a time-periodic electroosmotic flow of viscoelastic fluids in a slowly varying microchannel under the influence of a magnetic field. We consider the Jeffrey fluid model, which describes the linear viscoelastic fluid, and an effort is made to obtain the analytical solutions, considering velocity and thermal slip conditions at the fluid–solid interface. The study reveals that the relaxation and retardation times in the Jeffrey fluid have a significant effect on the axial velocity and temperature distribution within the microchannel. Further, we observed that the Joule heating contributes to enhanced thermal response in both temperature distribution and Nusselt number, leading to increased entropy generation. The Bejan number profiles enhance with an increase in the Joule heating parameter due to the conversion of electrical energy into thermal energy. The velocity slip enhances the rate of heat transfer and entropy generation, while these quantities decrease with the thermal slip. The present study on AC electroosmosis and electrothermal flow shows significant promise as a fluid-driven technique in microfluidics for future endeavors.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"111 ","pages":"Pages 176-187"},"PeriodicalIF":2.5,"publicationDate":"2025-01-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143093481","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 : 2025-01-18DOI: 10.1016/j.euromechflu.2025.01.002
Yakun Zhao , Huanyu Zhang , Shuyue Sun , Tao Peng , Gang Chen , Xinliang Tian
Wind tunnel experiments were conducted to study the flow normal to a flat plate attached with a closed flexible membrane. Two control parameters, the membrane width and the wind speed, were considered. A suspension device was designed to measure the aerodynamic forces exerted on the plate+membrane system. Experimental results show that, contingent on the membrane width, a significant drag reduction up to 22.2% is reported. Based on image recognition techniques, a measurement method using two high-speed cameras was developed to reconstruct the membrane’s motion. The time-averaged shape of the membrane is maintained as a plump D-shape cylinder. The membrane exhibits a rigid-body flapping motion and a bending deformation, accompanied by traveling waves along the membrane. Results of amplitude and standard deviation of the membrane motion show that the more intense flapping occurs on two sides of the membrane, while gentler flapping in the middle region. Furthermore, smoke-wire flow visualization reveals that the presence of the membrane significantly alters the flow structures in the delay in flow separation and the emergence of narrower wake structures, thus reducing drag. Our study demonstrates that such a flow control device using a flexible membrane coating is effective under 3D, high and turbulent flow conditions, which providing powerful evidence of its potential for practical engineering applications.
{"title":"A wind tunnel experimental investigation for the flow normal to a flat plate attached with a closed membrane coating","authors":"Yakun Zhao , Huanyu Zhang , Shuyue Sun , Tao Peng , Gang Chen , Xinliang Tian","doi":"10.1016/j.euromechflu.2025.01.002","DOIUrl":"10.1016/j.euromechflu.2025.01.002","url":null,"abstract":"<div><div>Wind tunnel experiments were conducted to study the flow normal to a flat plate attached with a closed flexible membrane. Two control parameters, the membrane width and the wind speed, were considered. A suspension device was designed to measure the aerodynamic forces exerted on the plate+membrane system. Experimental results show that, contingent on the membrane width, a significant drag reduction up to 22.2% is reported. Based on image recognition techniques, a measurement method using two high-speed cameras was developed to reconstruct the membrane’s motion. The time-averaged shape of the membrane is maintained as a plump D-shape cylinder. The membrane exhibits a rigid-body flapping motion and a bending deformation, accompanied by traveling waves along the membrane. Results of amplitude and standard deviation of the membrane motion show that the more intense flapping occurs on two sides of the membrane, while gentler flapping in the middle region. Furthermore, smoke-wire flow visualization reveals that the presence of the membrane significantly alters the flow structures in the delay in flow separation and the emergence of narrower wake structures, thus reducing drag. Our study demonstrates that such a flow control device using a flexible membrane coating is effective under 3D, high <span><math><mrow><mi>R</mi><mi>e</mi></mrow></math></span> and turbulent flow conditions, which providing powerful evidence of its potential for practical engineering applications.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"111 ","pages":"Pages 127-142"},"PeriodicalIF":2.5,"publicationDate":"2025-01-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143093519","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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