Pub Date : 2025-09-13DOI: 10.1016/j.euromechflu.2025.204366
Alexey E. Rastegin
Welander’s approach to study convective motions in a differentially spot-heated loop is reformulated for the case of fluid near the temperature of maximum density. The existence of this temperature is of great importance to understand dynamics of temperate lakes. The key character of the case of interest is that heat exchange takes place only within small spots at the bottom and the top of the loop. This study aims to reveal what happens with convective motions when fluid is near a state with the zero coefficient of thermal expansion. A somehow surprising conclusion is that steady regimes of convection, when they exist, turn out to be stable. This outcome differs from the case when heat exchange with the environment in line with Newton’s law of cooling takes place in a whole range of the loop. The findings of theoretical analysis are supported by the results of numerical studies. The reported outcomes allow us to estimate peculiarities of building more complex models of thermal convection. In particular, the role of spot-heated character of exchange with the environment is demonstrated. This feature should be kept in mind in attempts to simulate natural convection on the base of idealized models.
{"title":"On the stable convection in a differentially spot-heated loop near the temperature of maximum density","authors":"Alexey E. Rastegin","doi":"10.1016/j.euromechflu.2025.204366","DOIUrl":"10.1016/j.euromechflu.2025.204366","url":null,"abstract":"<div><div>Welander’s approach to study convective motions in a differentially spot-heated loop is reformulated for the case of fluid near the temperature of maximum density. The existence of this temperature is of great importance to understand dynamics of temperate lakes. The key character of the case of interest is that heat exchange takes place only within small spots at the bottom and the top of the loop. This study aims to reveal what happens with convective motions when fluid is near a state with the zero coefficient of thermal expansion. A somehow surprising conclusion is that steady regimes of convection, when they exist, turn out to be stable. This outcome differs from the case when heat exchange with the environment in line with Newton’s law of cooling takes place in a whole range of the loop. The findings of theoretical analysis are supported by the results of numerical studies. The reported outcomes allow us to estimate peculiarities of building more complex models of thermal convection. In particular, the role of spot-heated character of exchange with the environment is demonstrated. This feature should be kept in mind in attempts to simulate natural convection on the base of idealized models.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"115 ","pages":"Article 204366"},"PeriodicalIF":2.5,"publicationDate":"2025-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145106558","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 : 2025-09-12DOI: 10.1016/j.euromechflu.2025.204367
Janhavi K. Devnikar, Jayraj M. Chapare, Om M. Butle, P.W. Deshmukh, Pravin R. Kubade, Lalit K. Toke
Augmentation of heat transfer plays a crucial role in energy-saving options in modern thermal systems. These enhancement methods are passive with no external power source, and another is an active method where an external energy source is essential. The passive methods are more popular and the best energy-saving option, making the system more effective and efficient. The recent advancement in passive methods is a compound method consisting of alterations in the fluid containers and obstructions in fluid passages. In the prevailing study, the round tube is formed in the profile of a twisted tube, within which a twisted strip is placed. The twisted tube causes a reduction in the temperature and velocity gradients near the tube surface due to the twisting motion of the fluid at that region, whereas the central core portion of the fluid interacts thoroughly with the heated surface due to the presence of the twisted strip at the central portion of the twisted tube. This modified flow system enhanced heat transfer using air as a fluid in turbulent flow circumstances for Reynolds numbers ranging from 2500 to 17000. The present study indicates that the average improvement ratio, Nue/Nup, and average friction factor ratio, fe/fp, are 1.25–3.9 and 2.0–12.0, respectively, compared with the plain tube at the same flow rate conditions.
{"title":"Thermohydraulic performance of twisted circular tube (TCT) retrofitted with twisted strip (TS) insert","authors":"Janhavi K. Devnikar, Jayraj M. Chapare, Om M. Butle, P.W. Deshmukh, Pravin R. Kubade, Lalit K. Toke","doi":"10.1016/j.euromechflu.2025.204367","DOIUrl":"10.1016/j.euromechflu.2025.204367","url":null,"abstract":"<div><div>Augmentation of heat transfer plays a crucial role in energy-saving options in modern thermal systems. These enhancement methods are passive with no external power source, and another is an active method where an external energy source is essential. The passive methods are more popular and the best energy-saving option, making the system more effective and efficient. The recent advancement in passive methods is a compound method consisting of alterations in the fluid containers and obstructions in fluid passages. In the prevailing study, the round tube is formed in the profile of a twisted tube, within which a twisted strip is placed. The twisted tube causes a reduction in the temperature and velocity gradients near the tube surface due to the twisting motion of the fluid at that region, whereas the central core portion of the fluid interacts thoroughly with the heated surface due to the presence of the twisted strip at the central portion of the twisted tube. This modified flow system enhanced heat transfer using air as a fluid in turbulent flow circumstances for Reynolds numbers ranging from 2500 to 17000. The present study indicates that the average improvement ratio, <em>Nu</em><sub><em>e</em></sub><em>/Nu</em><sub><em>p</em></sub><em>,</em> and average friction factor ratio, <em>f</em><sub><em>e</em></sub><em>/f</em><sub><em>p</em></sub>, are 1.25–3.9 and 2.0–12.0, respectively, compared with the plain tube at the same flow rate conditions.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"115 ","pages":"Article 204367"},"PeriodicalIF":2.5,"publicationDate":"2025-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145106555","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 : 2025-09-10DOI: 10.1016/j.euromechflu.2025.204348
Aritras Roy , Rinku Mukherjee
<div><div>The ability of a morphed wing to prevent 3D flow separation when operating at high angles of attack and when the flow past it is unsteady is investigated. The wing is morphed using an external skin attached to the leading edge of the wing, which takes the shape of the suction/top surface of the wing, when not in use. When required, the external skin is deployed but with a new shape, which is a morphed version of the top surface of the wing and has the ability to prevent flow separation. The shape of the external skin is predicted using a numerical algorithm developed for this purpose that couples an Unsteady Vortex Lattice Method with another in-house steady-state Vortex Lattice Method algorithm that uses a ‘decambering’ concept to ‘correct’ the local camberline to account for flow separation. Physical wing models are then fabricated along with the numerically predicted morphed surfaces to be attached externally at the leading edge and tested in the wind tunnel. Unsteady change in angle of attack is implemented using an in-house mechanism developed for this purpose, where the rate of change of angle of attack, <span><math><mrow><mfrac><mrow><mi>∂</mi><mi>α</mi></mrow><mrow><mi>∂</mi><mi>t</mi></mrow></mfrac><mo>=</mo><mover><mrow><mi>α</mi></mrow><mrow><mo>̇</mo></mrow></mover></mrow></math></span> is varied as <span><math><mrow><mn>0</mn><mo>.</mo><mn>1</mn><mo>°</mo><mo>/</mo><mi>s</mi><mo><</mo><mover><mrow><mi>α</mi></mrow><mrow><mo>̇</mo></mrow></mover><mo><</mo><mn>1</mn><mo>°</mo><mo>/</mo><mi>s</mi></mrow></math></span>. Unsteady aerodynamic characteristics like <span><math><mrow><msub><mrow><mi>C</mi></mrow><mrow><mi>L</mi></mrow></msub><mrow><mo>(</mo><mi>t</mi><mo>)</mo></mrow><mo>,</mo><msub><mrow><mi>C</mi></mrow><mrow><mi>D</mi></mrow></msub><mrow><mo>(</mo><mi>t</mi><mo>)</mo></mrow><mo>,</mo><msub><mrow><mi>C</mi></mrow><mrow><mi>M</mi></mrow></msub><mrow><mo>(</mo><mi>t</mi><mo>)</mo></mrow></mrow></math></span> are measured for change in Reynolds number, <span><math><mrow><mn>0</mn><mo>.</mo><mn>045</mn><mo>×</mo><mn>1</mn><msup><mrow><mn>0</mn></mrow><mrow><mn>6</mn></mrow></msup><mo><</mo><mi>R</mi><mi>e</mi><mo><</mo><mn>0</mn><mo>.</mo><mn>1</mn><mo>×</mo><mn>1</mn><msup><mrow><mn>0</mn></mrow><mrow><mn>6</mn></mrow></msup></mrow></math></span>. Flow visualization using smoke is conducted in the wind tunnel. CFD is also used to study such a morphing wing at high angles of attack including at post-stall. Spectral densities of the transient load data, <span><math><mrow><msub><mrow><mi>C</mi></mrow><mrow><mi>L</mi></mrow></msub><mrow><mo>(</mo><mi>t</mi><mo>)</mo></mrow><mo>,</mo><msub><mrow><mi>C</mi></mrow><mrow><mi>D</mi></mrow></msub><mrow><mo>(</mo><mi>t</mi><mo>)</mo></mrow></mrow></math></span> and unsteady sectional lift coefficient, <span><math><mrow><msub><mrow><mi>C</mi></mrow><mrow><msub><mrow><mi>l</mi></mrow><mrow><mi>s</mi><mi>e</mi><mi>c</mi></mrow></msub></mrow></msub><mrow><mo>(</mo><mi>t
{"title":"Unsteady aerodynamics of the control of three dimensional flow separation by morphing a wing surface","authors":"Aritras Roy , Rinku Mukherjee","doi":"10.1016/j.euromechflu.2025.204348","DOIUrl":"10.1016/j.euromechflu.2025.204348","url":null,"abstract":"<div><div>The ability of a morphed wing to prevent 3D flow separation when operating at high angles of attack and when the flow past it is unsteady is investigated. The wing is morphed using an external skin attached to the leading edge of the wing, which takes the shape of the suction/top surface of the wing, when not in use. When required, the external skin is deployed but with a new shape, which is a morphed version of the top surface of the wing and has the ability to prevent flow separation. The shape of the external skin is predicted using a numerical algorithm developed for this purpose that couples an Unsteady Vortex Lattice Method with another in-house steady-state Vortex Lattice Method algorithm that uses a ‘decambering’ concept to ‘correct’ the local camberline to account for flow separation. Physical wing models are then fabricated along with the numerically predicted morphed surfaces to be attached externally at the leading edge and tested in the wind tunnel. Unsteady change in angle of attack is implemented using an in-house mechanism developed for this purpose, where the rate of change of angle of attack, <span><math><mrow><mfrac><mrow><mi>∂</mi><mi>α</mi></mrow><mrow><mi>∂</mi><mi>t</mi></mrow></mfrac><mo>=</mo><mover><mrow><mi>α</mi></mrow><mrow><mo>̇</mo></mrow></mover></mrow></math></span> is varied as <span><math><mrow><mn>0</mn><mo>.</mo><mn>1</mn><mo>°</mo><mo>/</mo><mi>s</mi><mo><</mo><mover><mrow><mi>α</mi></mrow><mrow><mo>̇</mo></mrow></mover><mo><</mo><mn>1</mn><mo>°</mo><mo>/</mo><mi>s</mi></mrow></math></span>. Unsteady aerodynamic characteristics like <span><math><mrow><msub><mrow><mi>C</mi></mrow><mrow><mi>L</mi></mrow></msub><mrow><mo>(</mo><mi>t</mi><mo>)</mo></mrow><mo>,</mo><msub><mrow><mi>C</mi></mrow><mrow><mi>D</mi></mrow></msub><mrow><mo>(</mo><mi>t</mi><mo>)</mo></mrow><mo>,</mo><msub><mrow><mi>C</mi></mrow><mrow><mi>M</mi></mrow></msub><mrow><mo>(</mo><mi>t</mi><mo>)</mo></mrow></mrow></math></span> are measured for change in Reynolds number, <span><math><mrow><mn>0</mn><mo>.</mo><mn>045</mn><mo>×</mo><mn>1</mn><msup><mrow><mn>0</mn></mrow><mrow><mn>6</mn></mrow></msup><mo><</mo><mi>R</mi><mi>e</mi><mo><</mo><mn>0</mn><mo>.</mo><mn>1</mn><mo>×</mo><mn>1</mn><msup><mrow><mn>0</mn></mrow><mrow><mn>6</mn></mrow></msup></mrow></math></span>. Flow visualization using smoke is conducted in the wind tunnel. CFD is also used to study such a morphing wing at high angles of attack including at post-stall. Spectral densities of the transient load data, <span><math><mrow><msub><mrow><mi>C</mi></mrow><mrow><mi>L</mi></mrow></msub><mrow><mo>(</mo><mi>t</mi><mo>)</mo></mrow><mo>,</mo><msub><mrow><mi>C</mi></mrow><mrow><mi>D</mi></mrow></msub><mrow><mo>(</mo><mi>t</mi><mo>)</mo></mrow></mrow></math></span> and unsteady sectional lift coefficient, <span><math><mrow><msub><mrow><mi>C</mi></mrow><mrow><msub><mrow><mi>l</mi></mrow><mrow><mi>s</mi><mi>e</mi><mi>c</mi></mrow></msub></mrow></msub><mrow><mo>(</mo><mi>t","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"115 ","pages":"Article 204348"},"PeriodicalIF":2.5,"publicationDate":"2025-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145026327","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 : 2025-09-08DOI: 10.1016/j.euromechflu.2025.204355
Simon Dalpke , Jiasheng Yang , Pourya Forooghi , Bettina Frohnapfel , Alexander Stroh
The influence of rough surfaces on fluid flow is characterized by the downward shift in the logarithmic layer of velocity and temperature profiles, namely the velocity roughness function and the corresponding temperature roughness function . Their computation relies on computational simulations, and hence a simple prediction without such simulation is envisioned. We present a framework where a data-driven model is developed using the dataset of Yang et al. 2023 [1] with 93 high-fidelity direct numerical simulations of a fully-developed turbulent channel flow at and . The model provides robust predictive capabilities (mean squared error and ), but lacks interpretability. Simplistic statistical roughness parameters provide a more understandable route, so the framework is extended with a symbolic regression approach to distill an empirical correlation from the data-driven model. The derived expression leads to a predictive correlation for the equivalent sand-grain roughness with reasonable predictive powers. The predictive capability of the temperature roughness function is subject to limitations due to the missing Prandtl number variation in the dataset. Nevertheless, the interpretable correlation and the neural network as well as the original dataset can be used to explore the roughness functions. The functional form of the derived correlations, along with visual analysis of these surfaces, suggests a strong relationship with roughness wavelengths, further linking them to explanations based on sheltered and windward regions.
{"title":"Data-driven correlations for thermohydraulic roughness properties","authors":"Simon Dalpke , Jiasheng Yang , Pourya Forooghi , Bettina Frohnapfel , Alexander Stroh","doi":"10.1016/j.euromechflu.2025.204355","DOIUrl":"10.1016/j.euromechflu.2025.204355","url":null,"abstract":"<div><div>The influence of rough surfaces on fluid flow is characterized by the downward shift in the logarithmic layer of velocity and temperature profiles, namely the velocity roughness function <span><math><mrow><mi>Δ</mi><msup><mrow><mi>U</mi></mrow><mrow><mo>+</mo></mrow></msup></mrow></math></span> and the corresponding temperature roughness function <span><math><mrow><mi>Δ</mi><msup><mrow><mi>Θ</mi></mrow><mrow><mo>+</mo></mrow></msup></mrow></math></span>. Their computation relies on computational simulations, and hence a simple prediction without such simulation is envisioned. We present a framework where a data-driven model is developed using the dataset of Yang et al. 2023 <span><span>[1]</span></span> with 93 high-fidelity direct numerical simulations of a fully-developed turbulent channel flow at <span><math><mrow><mi>R</mi><msub><mrow><mi>e</mi></mrow><mrow><mi>τ</mi></mrow></msub><mo>≈</mo><mn>800</mn></mrow></math></span> and <span><math><mrow><mi>P</mi><mi>r</mi><mo>=</mo><mn>0</mn><mo>.</mo><mn>71</mn></mrow></math></span>. The model provides robust predictive capabilities (mean squared error <span><math><mrow><msub><mrow><mtext>MSE</mtext></mrow><mrow><mi>k</mi></mrow></msub><mo>=</mo><mn>0</mn><mo>.</mo><mn>09</mn></mrow></math></span> and <span><math><mrow><msub><mrow><mtext>MSE</mtext></mrow><mrow><mi>θ</mi></mrow></msub><mo>=</mo><mn>0</mn><mo>.</mo><mn>096</mn></mrow></math></span>), but lacks interpretability. Simplistic statistical roughness parameters provide a more understandable route, so the framework is extended with a symbolic regression approach to distill an empirical correlation from the data-driven model. The derived expression leads to a predictive correlation for the equivalent sand-grain roughness <span><math><mrow><msub><mrow><mi>k</mi></mrow><mrow><mtext>s</mtext></mrow></msub><mo>=</mo><msub><mrow><mi>k</mi></mrow><mrow><mtext>99</mtext></mrow></msub><mrow><mo>(</mo><mi>E</mi><msub><mrow><mi>S</mi></mrow><mrow><mi>x</mi></mrow></msub><mrow><mo>(</mo><mo>−</mo><mi>E</mi><msub><mrow><mi>S</mi></mrow><mrow><mi>x</mi></mrow></msub><mo>+</mo><mi>S</mi><mi>k</mi><mo>+</mo><mn>2</mn><mo>.</mo><mn>37</mn><mo>)</mo></mrow><mo>+</mo><mn>0</mn><mo>.</mo><mn>772</mn><mo>)</mo></mrow></mrow></math></span> with reasonable predictive powers. The predictive capability of the temperature roughness function is subject to limitations due to the missing Prandtl number variation in the dataset. Nevertheless, the interpretable correlation and the neural network as well as the original dataset can be used to explore the roughness functions. The functional form of the derived correlations, along with visual analysis of these surfaces, suggests a strong relationship with roughness wavelengths, further linking them to explanations based on sheltered and windward regions.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"115 ","pages":"Article 204355"},"PeriodicalIF":2.5,"publicationDate":"2025-09-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145333091","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 : 2025-09-08DOI: 10.1016/j.euromechflu.2025.204356
Sarita Yadav, Geetanjali Chattopadhyay
The electrohydrodynamic stability of a two-layer plane Poiseuille flow has been considered under the influence of an electric field acting normally to the interface of the two viscous immiscible fluids. The two fluids considered here for the asymptotic stability analysis are leaky dielectrics. The study on the influence of a monolayer of insoluble surfactant at the fluid-fluid interface reveals that the interfacial surfactant further enhances or suppresses the electric field-induced instability. The long-wave linear stability analysis is carried out in the framework of Orr–Sommerfeld analysis for leaky dielectrics. In the context of long-wave linear stability study, the phase speed is expressed as a function of the ratio of viscosities (), layer thicknesses (), densities (), permittivities () and conductivities () of the two fluids. The electric field is observed to have either a destabilizing or a stabilizing effect, primarily non-monotonic, depending upon the ratios of permittivities and conductivities of the two fluids. It is found that when , the region of instability in the plane increases with increasing Marangoni number (); however, when , the scenario reverses. The electrohydrodynamic interface instability among two viscous fluids with varying electrical properties in plane Poiseuille flow has applications in microfluidic devices for mixing and droplet formation. Therefore, the present study aims to propose a control mechanism for the instability occurring at the interface through the modified interface tension.
{"title":"Role of insoluble surfactant on electrohydrodynamic stability of a two-layer plane Poiseuille flow: An asymptotic analysis","authors":"Sarita Yadav, Geetanjali Chattopadhyay","doi":"10.1016/j.euromechflu.2025.204356","DOIUrl":"10.1016/j.euromechflu.2025.204356","url":null,"abstract":"<div><div>The electrohydrodynamic stability of a two-layer plane Poiseuille flow has been considered under the influence of an electric field acting normally to the interface of the two viscous immiscible fluids. The two fluids considered here for the asymptotic stability analysis are leaky dielectrics. The study on the influence of a monolayer of insoluble surfactant at the fluid-fluid interface reveals that the interfacial surfactant further enhances or suppresses the electric field-induced instability. The long-wave linear stability analysis is carried out in the framework of Orr–Sommerfeld analysis for leaky dielectrics. In the context of long-wave linear stability study, the phase speed is expressed as a function of the ratio of viscosities (<span><math><mi>m</mi></math></span>), layer thicknesses (<span><math><mi>d</mi></math></span>), densities (<span><math><mi>r</mi></math></span>), permittivities (<span><math><mi>ɛ</mi></math></span>) and conductivities (<span><math><mi>l</mi></math></span>) of the two fluids. The electric field is observed to have either a destabilizing or a stabilizing effect, primarily non-monotonic, depending upon the ratios of permittivities and conductivities of the two fluids. It is found that when <span><math><mrow><mi>m</mi><mo>></mo><msup><mrow><mi>d</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math></span>, the region of instability in the <span><math><mrow><mi>ɛ</mi><mo>−</mo><mi>l</mi></mrow></math></span> plane increases with increasing Marangoni number (<span><math><mrow><mi>M</mi><mi>a</mi></mrow></math></span>); however, when <span><math><mrow><mi>m</mi><mo><</mo><msup><mrow><mi>d</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math></span>, the scenario reverses. The electrohydrodynamic interface instability among two viscous fluids with varying electrical properties in plane Poiseuille flow has applications in microfluidic devices for mixing and droplet formation. Therefore, the present study aims to propose a control mechanism for the instability occurring at the interface through the modified interface tension.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"115 ","pages":"Article 204356"},"PeriodicalIF":2.5,"publicationDate":"2025-09-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145047215","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}
Flight feathers of birds are featured by the typical herringbone pattern, which is consisted of a central shaft and divergent barbs on both sides. In this work, bio-inspired herringbone riblets are embedded into the suction side of a NACA0012 airfoil model, with an attempt to explore their roles on the flow and fluid force. Experiments are conducted in a water tunnel at a Reynolds number of Re = 2 × 105, based on incoming freestream velocity and airfoil cord length c. While the lift and drag forces of the airfoil model are measured by a load cell, flow fields over the suction side of the airfoil model are captured by the particle image velocimetry (PIV) technique. The herringbone-ribbed suction side of the airfoil model is defined by the divergent angle β (= 60°) of the riblets, the spanwise wavelength λ (= 0.2c and 0.4c) of the repeating herringbone pattern, as well as the riblet height h (= 0.6 %c and 1.2 %c). Results from the force measurements reveal that the airfoil models with the herringbone-ribbed suction side outperform their smooth counterparts and the baseline NACA0012 model, with the stall being significantly postponed from 10° to over 16° while the maximum time-mean lift coefficient being remained nearly unaffected. This is attributed to the transition from laminar to turbulent boundary layers, thus associated with substantially suppressed flow separation, over the airfoil models with the bio-inspired riblets being covered on the suction side. On the other hand, it is observed that the time-mean lift coefficient is considerably reduced whilst the drag coefficient is marginally increased at the angle of attack α < 12° for the airfoil models with the bio-inspired riblets being covered on the suction side, compared with those of their smooth counterparts and the baseline NACA0012 model.
{"title":"Flow over airfoil model covered by bio-inspired herringbone riblets","authors":"Haoxiang He, Honglei Bai, Shixiong Zhang, Zan Zhang","doi":"10.1016/j.euromechflu.2025.204365","DOIUrl":"10.1016/j.euromechflu.2025.204365","url":null,"abstract":"<div><div>Flight feathers of birds are featured by the typical herringbone pattern, which is consisted of a central shaft and divergent barbs on both sides. In this work, bio-inspired herringbone riblets are embedded into the suction side of a NACA0012 airfoil model, with an attempt to explore their roles on the flow and fluid force. Experiments are conducted in a water tunnel at a Reynolds number of <em>Re</em> = 2 × 10<sup>5</sup>, based on incoming freestream velocity and airfoil cord length <em>c</em>. While the lift and drag forces of the airfoil model are measured by a load cell, flow fields over the suction side of the airfoil model are captured by the particle image velocimetry (PIV) technique. The herringbone-ribbed suction side of the airfoil model is defined by the divergent angle <em>β</em> (= 60°) of the riblets, the spanwise wavelength <em>λ</em> (= 0.2<em>c</em> and 0.4<em>c</em>) of the repeating herringbone pattern, as well as the riblet height <em>h</em> (= 0.6 %<em>c</em> and 1.2 %<em>c</em>). Results from the force measurements reveal that the airfoil models with the herringbone-ribbed suction side outperform their smooth counterparts and the baseline NACA0012 model, with the stall being significantly postponed from 10° to over 16° while the maximum time-mean lift coefficient being remained nearly unaffected. This is attributed to the transition from laminar to turbulent boundary layers, thus associated with substantially suppressed flow separation, over the airfoil models with the bio-inspired riblets being covered on the suction side. On the other hand, it is observed that the time-mean lift coefficient is considerably reduced whilst the drag coefficient is marginally increased at the angle of attack <em>α</em> < 12° for the airfoil models with the bio-inspired riblets being covered on the suction side, compared with those of their smooth counterparts and the baseline NACA0012 model.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"115 ","pages":"Article 204365"},"PeriodicalIF":2.5,"publicationDate":"2025-09-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145106557","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 : 2025-09-02DOI: 10.1016/j.euromechflu.2025.204345
Deepak Kumar, Subramaniam Pushpavanam
Aqueous humor dynamics is responsible for maintaining intraocular pressure, ocular health and targeted drug delivery within the eye. This study investigates the flow of AH within the anterior chamber under the combined influence of a uniform magnetic field and natural convection. Different orientations of the magnetic field and temperature gradient are considered. A lubrication approximation is employed and the resulting equations are solved using regular perturbation method. The analytical solutions are validated using numerical simulations performed in COMSOL Multiphysics 6.2protect relax special {t4ht=®}. In the standing position, AH flow field is characterized by a single vortex, while in the supine position, it forms two counter-rotating vortices. The velocity is found to be higher in standing position. The effect of a uniform magnetic field on the velocity is more significant in the supine position. The magnetic field does not change the flow field qualitatively as buoyancy is the primary driving force. In the standing position a magnetic field oriented perpendicular to the eye resulted in a greatest reduction of AH velocity, as compared to a magnetic field along the eye. The use of magnetic fields is being considered as a disruptive technology in ocular treatment. This study establishes that magnetic fields provide a holistic approach for targeted drug delivery in ocular treatment. They can be used without fear of any risks as the flow patterns in AH are not qualitatively modified.
房水动力学负责维持眼压、眼健康和眼内靶向药物输送。本研究考察了均匀磁场和自然对流共同作用下前房AH的流动情况。考虑了不同方向的磁场和温度梯度。采用润滑近似，用正则摄动法求解得到的方程。利用COMSOL Multiphysics 6.2protect relax special {t4ht=®}进行的数值模拟验证了解析解的有效性。在站立位置时，AH流场的特征为单个涡，而在仰卧位置时，它形成两个反向旋转的涡。发现站姿时速度更高。平卧位时，均匀磁场对速度的影响更为显著。由于浮力是主要的驱动力，磁场不会对流场产生质的改变。与沿眼睛方向的磁场相比，在站立位置垂直于眼睛方向的磁场导致AH速度的最大降低。磁场的使用被认为是眼部治疗中的一项颠覆性技术。本研究确定磁场为眼部治疗的靶向药物递送提供了一种整体方法。它们可以使用而不必担心任何风险，因为AH中的流模式没有进行定性修改。
{"title":"How safe are magnetic fields in enhancing drug delivery in ocular treatment? Hydrodynamic aspects","authors":"Deepak Kumar, Subramaniam Pushpavanam","doi":"10.1016/j.euromechflu.2025.204345","DOIUrl":"10.1016/j.euromechflu.2025.204345","url":null,"abstract":"<div><div>Aqueous humor dynamics is responsible for maintaining intraocular pressure, ocular health and targeted drug delivery within the eye. This study investigates the flow of AH within the anterior chamber under the combined influence of a uniform magnetic field and natural convection. Different orientations of the magnetic field and temperature gradient are considered. A lubrication approximation is employed and the resulting equations are solved using regular perturbation method. The analytical solutions are validated using numerical simulations performed in COMSOL Multiphysics 6.2<sup>protect relax special {t4ht=®}</sup>. In the standing position, AH flow field is characterized by a single vortex, while in the supine position, it forms two counter-rotating vortices. The velocity is found to be higher in standing position. The effect of a uniform magnetic field on the velocity is more significant in the supine position. The magnetic field does not change the flow field qualitatively as buoyancy is the primary driving force. In the standing position a magnetic field oriented perpendicular to the eye resulted in a greatest reduction of AH velocity, as compared to a magnetic field along the eye. The use of magnetic fields is being considered as a disruptive technology in ocular treatment. This study establishes that magnetic fields provide a holistic approach for targeted drug delivery in ocular treatment. They can be used without fear of any risks as the flow patterns in AH are not qualitatively modified.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"115 ","pages":"Article 204345"},"PeriodicalIF":2.5,"publicationDate":"2025-09-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145026325","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 : 2025-08-30DOI: 10.1016/j.euromechflu.2025.204354
Dhrubajyoti Kashyap
This study explores the intricate dynamics of a mixed convection phenomenon in a cavity filled with nanofluid while employing a novel approach based on the two-phase lattice Boltzmann method (LBM) with multiple-relaxation-time (MRT). The introduction of a permeable hot square block with blockage ratios (BR) of 0.25 and 0.5 further augmenting the complexity of the phenomena. The current research aims to evaluate the effectiveness of the two-phase MRT-LBM approach in analyzing the slip mechanisms of nanofluids and drag forces within porous media, while making rigorous validation against established experimental and numerical benchmarks. A comprehensive parametric study is conducted by varying the nanoparticle concentration of Al2O3/water nanofluid (, Richardson numbers (0.1), and permeability of the inner block (10−2Da 10−6) to assess their impact on flow structure, thermal field, and entropy distribution. The results demonstrate that increasing enhances thermal conductivity and improves heat transfer, while simultaneously increasing viscous dissipation and entropy generation. Permeability plays a crucial role in governing flow penetration and heat transfer performance, transitioning the system from conduction- to convection-dominated regimes. The blockage ratio critically impacts performance: at low Ri, BR = 0.5 boosts heat transfer through enhanced shear and localized thermal gradients, whereas at high Ri, BR = 0.25 improves efficiency by minimising flow resistance and promoting smoother circulation. The outcome of this research sheds light on the interactions between the permeable block, nanofluid, and mixed convection effects and reveals that nanofluid usage can be thermodynamically advantageous under optimised flow conditions.
{"title":"Simulation of mixed convection in a nanofluid-filled cavity with inner hot permeable block: A two-phase MRT-LBM approach","authors":"Dhrubajyoti Kashyap","doi":"10.1016/j.euromechflu.2025.204354","DOIUrl":"10.1016/j.euromechflu.2025.204354","url":null,"abstract":"<div><div>This study explores the intricate dynamics of a mixed convection phenomenon in a cavity filled with nanofluid while employing a novel approach based on the two-phase lattice Boltzmann method (LBM) with multiple-relaxation-time (MRT). The introduction of a permeable hot square block with blockage ratios (<em>BR</em>) of 0.25 and 0.5 further augmenting the complexity of the phenomena. The current research aims to evaluate the effectiveness of the two-phase MRT-LBM approach in analyzing the slip mechanisms of nanofluids and drag forces within porous media, while making rigorous validation against established experimental and numerical benchmarks. A comprehensive parametric study is conducted by varying the nanoparticle concentration of Al<sub>2</sub>O<sub>3</sub>/water nanofluid (<span><math><mrow><mi>φ</mi><mo>≤</mo><mn>0.03</mn><mo>)</mo></mrow></math></span>, Richardson numbers (0.1<span><math><mrow><mo>≤</mo><mi>Ri</mi><mo>≤</mo><mn>10</mn></mrow></math></span>), and permeability of the inner block (10<sup>−2</sup> <span><math><mo>≤</mo></math></span> <em>Da</em> <span><math><mo>≤</mo></math></span> 10<sup>−6</sup>) to assess their impact on flow structure, thermal field, and entropy distribution. The results demonstrate that increasing <span><math><mi>φ</mi></math></span> enhances thermal conductivity and improves heat transfer, while simultaneously increasing viscous dissipation and entropy generation. Permeability plays a crucial role in governing flow penetration and heat transfer performance, transitioning the system from conduction- to convection-dominated regimes. The blockage ratio critically impacts performance: at low <em>Ri</em>, <em>BR</em> = 0.5 boosts heat transfer through enhanced shear and localized thermal gradients, whereas at high <em>Ri</em>, <em>BR</em> = 0.25 improves efficiency by minimising flow resistance and promoting smoother circulation. The outcome of this research sheds light on the interactions between the permeable block, nanofluid, and mixed convection effects and reveals that nanofluid usage can be thermodynamically advantageous under optimised flow conditions.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"114 ","pages":"Article 204354"},"PeriodicalIF":2.5,"publicationDate":"2025-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144917118","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 : 2025-08-27DOI: 10.1016/j.euromechflu.2025.204353
Ataollah Gharechae, Mohammad Reza Negahdari, Mehdi Rezapour
This study explores the hydrodynamic interaction of water waves with arrays of submerged horizontal permeable cylinders using Darcy's law and linear wave theory. A semi-analytical model, based on the eigenfunction expansion method, is developed to investigate wave attenuation, added mass, and damping coefficients. The developed model is validated against results from the existing literature. The analysis investigates the effects of permeability, submergence depth, and wave characteristics — including the dimensionless wavenumber (, where is the wavenumber, and denotes the cylinder radius) and porosity parameter (). The findings demonstrate that wave attenuation is most effective at moderate permeability () and wavenumbers in the range to 0.5, achieving energy dissipation levels of approximately 20 %. At higher permeability (), wave attenuation and damping coefficients approach zero, as the cylinders behave almost as if they were absent. The added mass decreases with increasing permeability and becomes nearly constant for . Notably, damping coefficients for intact cylinders are generally higher than those of permeable cylinders near the free surface, except at , where minimum damping occurs. These findings offer valuable guidance for optimizing the design of permeable marine structures, including wave dissipators, aquaculture systems, and offshore infrastructure, by tailoring permeability and geometry for enhanced performance and durability.
{"title":"Interaction of water waves with an array of permeable horizontal submerged cylinders","authors":"Ataollah Gharechae, Mohammad Reza Negahdari, Mehdi Rezapour","doi":"10.1016/j.euromechflu.2025.204353","DOIUrl":"10.1016/j.euromechflu.2025.204353","url":null,"abstract":"<div><div>This study explores the hydrodynamic interaction of water waves with arrays of submerged horizontal permeable cylinders using Darcy's law and linear wave theory. A semi-analytical model, based on the eigenfunction expansion method, is developed to investigate wave attenuation, added mass, and damping coefficients. The developed model is validated against results from the existing literature. The analysis investigates the effects of permeability, submergence depth, and wave characteristics — including the dimensionless wavenumber (<span><math><mi>Ka</mi></math></span>, where <span><math><mi>K</mi></math></span> is the wavenumber, and <span><math><mi>a</mi></math></span> denotes the cylinder radius) and porosity parameter (<span><math><msub><mrow><mi>G</mi></mrow><mrow><mn>0</mn></mrow></msub></math></span>). The findings demonstrate that wave attenuation is most effective at moderate permeability (<span><math><mrow><msub><mrow><mi>G</mi></mrow><mrow><mn>0</mn></mrow></msub><mo>=</mo><mn>0.5</mn></mrow></math></span>) and wavenumbers in the range <span><math><mrow><mi>Ka</mi><mo>=</mo><mn>0.3</mn></mrow></math></span> to 0.5, achieving energy dissipation levels of approximately 20 %. At higher permeability (<span><math><mrow><msub><mrow><mi>G</mi></mrow><mrow><mn>0</mn></mrow></msub><mo>≥</mo><mn>5</mn></mrow></math></span>), wave attenuation and damping coefficients approach zero, as the cylinders behave almost as if they were absent. The added mass decreases with increasing permeability and becomes nearly constant for <span><math><mrow><mi>Ka</mi><mo>></mo><mn>1</mn></mrow></math></span>. Notably, damping coefficients for intact cylinders are generally higher than those of permeable cylinders near the free surface, except at <span><math><mrow><mi>Ka</mi><mo>=</mo><mn>0.5</mn></mrow></math></span>, where minimum damping occurs. These findings offer valuable guidance for optimizing the design of permeable marine structures, including wave dissipators, aquaculture systems, and offshore infrastructure, by tailoring permeability and geometry for enhanced performance and durability.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"114 ","pages":"Article 204353"},"PeriodicalIF":2.5,"publicationDate":"2025-08-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144912932","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 : 2025-08-27DOI: 10.1016/j.euromechflu.2025.204352
Ziyuan Xu , Shenglong Gu , Hang Wang
We propose a hybrid model driven by both data and physics, termed Double-branched Physics-Informed Neural Network (Db-PINN), which enhances the synergy between data-driven and physical mechanisms methods, effectively improving the accuracy of predicting the hydraulic jump flow field and energy dissipation rate. The core architecture of the model is based on Convolutional Neural Networks (CNNs), which extract detailed features of the hydraulic jump flow field. In combination with a branch network, Deep Neural Networks (DNNs) are used to compute the residuals of partial differential equations, ensuring adherence to physical laws. Additionally, considering hardware resource constraints, the Db-PINN model incorporates a mini-batch algorithm to reduce dependence on GPU memory size, thus meeting the model’s need to process large-scale datasets. When compared to numerical simulation results, the model demonstrates high accuracy and generalization capability in predicting the velocity distribution and turbulence characteristics of the hydraulic jump flow field.
{"title":"Application of the Db-PINN model in predicting hydraulic jump flow fields under different Froude numbers","authors":"Ziyuan Xu , Shenglong Gu , Hang Wang","doi":"10.1016/j.euromechflu.2025.204352","DOIUrl":"10.1016/j.euromechflu.2025.204352","url":null,"abstract":"<div><div>We propose a hybrid model driven by both data and physics, termed Double-branched Physics-Informed Neural Network (Db-PINN), which enhances the synergy between data-driven and physical mechanisms methods, effectively improving the accuracy of predicting the hydraulic jump flow field and energy dissipation rate. The core architecture of the model is based on Convolutional Neural Networks (CNNs), which extract detailed features of the hydraulic jump flow field. In combination with a branch network, Deep Neural Networks (DNNs) are used to compute the residuals of partial differential equations, ensuring adherence to physical laws. Additionally, considering hardware resource constraints, the Db-PINN model incorporates a mini-batch algorithm to reduce dependence on GPU memory size, thus meeting the model’s need to process large-scale datasets. When compared to numerical simulation results, the model demonstrates high accuracy and generalization capability in predicting the velocity distribution and turbulence characteristics of the hydraulic jump flow field.</div></div>","PeriodicalId":11985,"journal":{"name":"European Journal of Mechanics B-fluids","volume":"115 ","pages":"Article 204352"},"PeriodicalIF":2.5,"publicationDate":"2025-08-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145005382","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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