Pub Date : 2024-09-19DOI: 10.1103/physrevfluids.9.094803
Z. Taebel, M. L. McAllister, A. Scotti, M. Onorato, T. S. van den Bremer
The statistical treatment of random weakly nonlinear interactions between waves, called wave turbulence (WT), is fundamental to understanding the development of the ocean surface. For gravity waves, wave turbulence predicts a dual (direct and inverse) cascade of energy and wave action, which yield power-law solutions for the energy spectrum. While energy cascades were predicted more than 50 years ago, observing them in the laboratory with mechanical forcing remains a challenge. Here, we present experiments in which we attempted to reproduce both direct and inverse cascades in a large circular wave tank. The geometry of the wave tank allows for the creation of isotropically spread surface waves, which is an assumption that underlies WT theory. Although we did see evidence of a direct cascade of energy, we did not observe an inverse cascade of wave action. We discuss the competing effects of dissipation and intermittency, which may dominate or obscure the weakly nonlinear dynamics.
{"title":"Laboratory study of wave turbulence under isotropic forcing","authors":"Z. Taebel, M. L. McAllister, A. Scotti, M. Onorato, T. S. van den Bremer","doi":"10.1103/physrevfluids.9.094803","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.094803","url":null,"abstract":"The statistical treatment of random weakly nonlinear interactions between waves, called wave turbulence (WT), is fundamental to understanding the development of the ocean surface. For gravity waves, wave turbulence predicts a dual (direct and inverse) cascade of energy and wave action, which yield power-law solutions for the energy spectrum. While energy cascades were predicted more than 50 years ago, observing them in the laboratory with mechanical forcing remains a challenge. Here, we present experiments in which we attempted to reproduce both direct and inverse cascades in a large circular wave tank. The geometry of the wave tank allows for the creation of isotropically spread surface waves, which is an assumption that underlies WT theory. Although we did see evidence of a direct cascade of energy, we did not observe an inverse cascade of wave action. We discuss the competing effects of dissipation and intermittency, which may dominate or obscure the weakly nonlinear dynamics.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"26 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142251968","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-19DOI: 10.1103/physrevfluids.9.093604
Yuxue Zhong, Jingzhu Wang, Jianlin Huang, Yiwei Wang
The collapse of a spark-induced bubble results in a high-speed jet, and when that jet impacts an elastic membrane, the latter deforms considerably and is accompanied by secondary cavitation. The cavitation bubble then moves away from the membrane with subsequent oscillation. To study the mechanism for this cavitation, experiments involving diffuse light and particle image velocimetry were conducted to capture the behaviors of the cavitation bubble and flow field resulting from the rapid deformation of the membrane. Analyzing the velocity and pressure fields reveals secondary cavitation induced by a sudden acceleration rather than a large velocity. Secondary cavitation occurs when the dimensionless inertial force overcomes the dimensionless pressure difference required for cavitation; subjecting these dimensionless quantities to a parametric study shows that the secondary cavitation occurs when the former is greater than the latter. During the collapse of the cavitation bubble, a thin jet points toward the membrane with an impact velocity of approximately 35 m/s. The subsequent oscillation of the cavitation bubble results in vortex flow moving away from the membrane. These findings provide insights into engineering applications such as bioengineering and mixing.
{"title":"Cavitation caused by an elastic membrane deforming under the jetting of a spark-induced bubble","authors":"Yuxue Zhong, Jingzhu Wang, Jianlin Huang, Yiwei Wang","doi":"10.1103/physrevfluids.9.093604","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.093604","url":null,"abstract":"The collapse of a spark-induced bubble results in a high-speed jet, and when that jet impacts an elastic membrane, the latter deforms considerably and is accompanied by secondary cavitation. The cavitation bubble then moves away from the membrane with subsequent oscillation. To study the mechanism for this cavitation, experiments involving diffuse light and particle image velocimetry were conducted to capture the behaviors of the cavitation bubble and flow field resulting from the rapid deformation of the membrane. Analyzing the velocity and pressure fields reveals secondary cavitation induced by a sudden acceleration rather than a large velocity. Secondary cavitation occurs when the dimensionless inertial force overcomes the dimensionless pressure difference required for cavitation; subjecting these dimensionless quantities to a parametric study shows that the secondary cavitation occurs when the former is greater than the latter. During the collapse of the cavitation bubble, a thin jet points toward the membrane with an impact velocity of approximately 35 m/s. The subsequent oscillation of the cavitation bubble results in vortex flow moving away from the membrane. These findings provide insights into engineering applications such as bioengineering and mixing.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"5 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142251967","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-17DOI: 10.1103/physrevfluids.9.093603
Kyle I. McKee, Bauyrzhan K. Primkulov, Kotaro Hashimoto, Yoshiyuki Tagawa, John W. M. Bush
In recent experiments, [E. Sawaguchi et al., J. Fluid Mech.862, 261 (2019)] directly probed the lubrication layer of air beneath a droplet levitating inside a rotating cylindrical drum. For small rotation rates of the drum, the lubrication film beneath the drop adopted a steady shape, while at higher rotation rates, traveling waves propagated along the drop's lower surface with roughly half the wall velocity. Here, we rationalize the physical origin of these waves. We begin with a simplified model of the lubrication flow beneath the droplet, and examine the linear stability of this base state to perturbations of the Tollmien-Schlichting type. Our developments lead to the Orr-Sommerfeld equation (OSE), whose eigenvalues give the growth rates and phase speeds of the perturbations. By considering wavelengths long relative to the lubrication film thickness, we solve the OSE perturbatively and so deduce the wavelength and phase velocity of the most unstable mode. We find satisfactory agreement between experiment and theory over the parameter regime considered in the laboratory.
{"title":"Waves beneath a drop levitating over a moving wall","authors":"Kyle I. McKee, Bauyrzhan K. Primkulov, Kotaro Hashimoto, Yoshiyuki Tagawa, John W. M. Bush","doi":"10.1103/physrevfluids.9.093603","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.093603","url":null,"abstract":"In recent experiments, [E. Sawaguchi <i>et al.</i>, <span>J. Fluid Mech.</span> <b>862</b>, 261 (2019)] directly probed the lubrication layer of air beneath a droplet levitating inside a rotating cylindrical drum. For small rotation rates of the drum, the lubrication film beneath the drop adopted a steady shape, while at higher rotation rates, traveling waves propagated along the drop's lower surface with roughly half the wall velocity. Here, we rationalize the physical origin of these waves. We begin with a simplified model of the lubrication flow beneath the droplet, and examine the linear stability of this base state to perturbations of the Tollmien-Schlichting type. Our developments lead to the Orr-Sommerfeld equation (OSE), whose eigenvalues give the growth rates and phase speeds of the perturbations. By considering wavelengths long relative to the lubrication film thickness, we solve the OSE perturbatively and so deduce the wavelength and phase velocity of the most unstable mode. We find satisfactory agreement between experiment and theory over the parameter regime considered in the laboratory.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"36 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142268723","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-16DOI: 10.1103/physrevfluids.9.094005
P. Pirdavari, H. Tran, Z. He, M. Y. Pack
This study reports the ability with which surface tension gradients are formed plainly by the drainage in a capillary containing a surfactant-laden liquid slug initially held in place by a vacuum. Provided that a thin film forms on the walls transverse to the downward flow, the drainage induces a surfactant gradient (i.e., Marangoni effect), which then leads to a film-climbing event against gravity. The overall climbing effect is limited by the capillary rise height (i.e., propensity for infiltration due to surface tension) and the surfactant gradient formed postmeniscus drainage, thus revealing a twofold role of surface tension in gravity-oriented capillaries hitherto unexplored. The interplay of mechanisms influencing the climbing films include surfactant kinetics, diffusion, and advection of surfactants.
{"title":"Drainage-induced spontaneous film climbing in capillaries","authors":"P. Pirdavari, H. Tran, Z. He, M. Y. Pack","doi":"10.1103/physrevfluids.9.094005","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.094005","url":null,"abstract":"This study reports the ability with which surface tension gradients are formed plainly by the drainage in a capillary containing a surfactant-laden liquid slug initially held in place by a vacuum. Provided that a thin film forms on the walls transverse to the downward flow, the drainage induces a surfactant gradient (i.e., Marangoni effect), which then leads to a film-climbing event against gravity. The overall climbing effect is limited by the capillary rise height (i.e., propensity for infiltration due to surface tension) and the surfactant gradient formed postmeniscus drainage, thus revealing a twofold role of surface tension in gravity-oriented capillaries hitherto unexplored. The interplay of mechanisms influencing the climbing films include surfactant kinetics, diffusion, and advection of surfactants.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"65 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142251970","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-16DOI: 10.1103/physrevfluids.9.093602
Huiyong Feng, Haibo Huang, Jian Hou, Chao Li, Bei Wei
This work explores the variation of viscosity of capsule suspension during the process of capsule rupture and polymer release using the immersed-boundary lattice Boltzmann method. The variation of viscosity is classified into three stages in the rupture process: the deformation stage, the rupture stage, and the stable stage. In the process of polymer release, two new stages of the variation of viscosity emerge: the diffusion stage and the dilution stage. Furthermore, the influence of viscosity ratio () on the viscosity is investigated. We find that the effective viscosity grows with and approaches the solid particle limit for very large , reflecting a similar behavior in the capsule shape. Finally, an available law that relates suspension viscosity to , capillary number (), and volume fraction () is established. The findings of this research have potential applications in fields such as oil exploration and capsule transportation.
{"title":"Viscosity of capsule suspensions: Effects of internal-external viscosity ratio and capsule rupture release","authors":"Huiyong Feng, Haibo Huang, Jian Hou, Chao Li, Bei Wei","doi":"10.1103/physrevfluids.9.093602","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.093602","url":null,"abstract":"This work explores the variation of viscosity of capsule suspension during the process of capsule rupture and polymer release using the immersed-boundary lattice Boltzmann method. The variation of viscosity is classified into three stages in the rupture process: the deformation stage, the rupture stage, and the stable stage. In the process of polymer release, two new stages of the variation of viscosity emerge: the diffusion stage and the dilution stage. Furthermore, the influence of viscosity ratio (<math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>λ</mi></math>) on the viscosity is investigated. We find that the effective viscosity grows with <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>λ</mi></math> and approaches the solid particle limit for very large <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>λ</mi></math>, reflecting a similar behavior in the capsule shape. Finally, an available law that relates suspension viscosity to <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>λ</mi></math>, capillary number (<math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>Ca</mi></math>), and volume fraction (<math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>ϕ</mi></math>) is established. The findings of this research have potential applications in fields such as oil exploration and capsule transportation.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"7 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142251969","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-16DOI: 10.1103/physrevfluids.9.093903
Basheer A. Khan, Shai Arogeti, Alexander Yakhot
The crisis (or critical) Reynolds number () is established at 1870, describing the threshold beyond which the lifetimes of turbulent puffs prior to the relaminarization extend from time units (), where and denote the pipe diameter and mean velocity, respectively. To analyze the role of inplane motion for sustaining turbulence, fully resolved direct numerical simulations have been performed to generate a localized, equilibrium turbulent puff at . Employing our approach based on proper orthogonal decomposition, the research confirms that azimuthal motion significantly contributes to the transition to turbulence. Notably, at supercritical Reynolds numbers () ranging from to , reducing azimuthal motion energy by 80% substantially shortens the lifetime of turbulent puffs. It has been shown that the relaminarization of turbulent puffs at subcritical Reynolds numbers, , clearly implies an exponential time decay of turbulence energy. The expression for the decay rate was obtained as a best-fit curve of direct numerical simulations.
危机（或临界）雷诺数（Rec）确定为 1870，描述了湍流涌在再层流化之前的寿命从 O(104)-O(106) 个时间单位（D/Um）（其中 D 和 Um 分别表示管道直径和平均速度）所超过的临界值。为了分析平面内运动对维持湍流的作用，我们进行了完全解析的直接数值模拟，以产生 Re=1920 的局部平衡湍流泡。采用我们基于适当正交分解的方法，研究证实方位运动对湍流的过渡有显著作用。值得注意的是，在 Re=1920 到 Re=2100 的超临界雷诺数（Re>Rec）范围内，减少 80% 的方位角运动能量会大大缩短湍流泡的寿命。研究表明，在次临界雷诺数（Re=1720-1840）下，湍流泡的再层流化明显意味着湍流能量的指数时间衰减。衰减率的表达式是通过直接数值模拟得到的最佳拟合曲线。
{"title":"Examination of the onset and decay of turbulence in pipe flow","authors":"Basheer A. Khan, Shai Arogeti, Alexander Yakhot","doi":"10.1103/physrevfluids.9.093903","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.093903","url":null,"abstract":"The crisis (or critical) Reynolds number (<math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mtext>Re</mtext><mi>c</mi></msub></math>) is established at 1870, describing the threshold beyond which the lifetimes of turbulent puffs prior to the relaminarization extend from <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mi>O</mi><mrow><mo>(</mo><msup><mn>10</mn><mn>4</mn></msup><mo>)</mo></mrow><mspace width=\"0.16em\"></mspace><mtext>to</mtext><mspace width=\"0.16em\"></mspace><mi>O</mi><mrow><mo>(</mo><msup><mn>10</mn><mn>6</mn></msup><mo>)</mo></mrow></mrow></math> time units (<math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mi>D</mi><mo>/</mo><msub><mi>U</mi><mi>m</mi></msub></mrow></math>), where <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>D</mi></math> and <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>U</mi><mi>m</mi></msub></math> denote the pipe diameter and mean velocity, respectively. To analyze the role of inplane motion for sustaining turbulence, fully resolved direct numerical simulations have been performed to generate a localized, equilibrium turbulent puff at <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mtext>Re</mtext><mo>=</mo><mn>1920</mn></mrow></math>. Employing our approach based on proper orthogonal decomposition, the research confirms that azimuthal motion significantly contributes to the transition to turbulence. Notably, at supercritical Reynolds numbers (<math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mtext>Re</mtext><mo>></mo><msub><mtext>Re</mtext><mi>c</mi></msub></mrow></math>) ranging from <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mtext>Re</mtext><mo>=</mo><mn>1920</mn></mrow></math> to <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mtext>Re</mtext><mo>=</mo><mn>2100</mn></mrow></math>, reducing azimuthal motion energy by 80% substantially shortens the lifetime of turbulent puffs. It has been shown that the relaminarization of turbulent puffs at subcritical Reynolds numbers, <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mtext>Re</mtext><mo>=</mo><mn>1720</mn><mtext>–</mtext><mn>1840</mn></mrow></math>, clearly implies an exponential time decay of turbulence energy. The expression for the decay rate was obtained as a best-fit curve of direct numerical simulations.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"14 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142268450","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-13DOI: 10.1103/physrevfluids.9.094004
Palas Kumar Farsoiya, Stéphane Popinet, Howard A. Stone, Luc Deike
Improved numerical methods are needed to understand the effect of surfactants in interfacial fluid mechanics, with various applications including thin films, inkjet printing, and ocean-atmosphere interactions. We provide a three-dimensional coupled volume of fluid (VoF) and phase field numerical approach to simulate the effects of insoluble surfactant-laden flows. The framework is validated against analytical cases for surfactant transport and Marangoni stresses. We then systematically investigate a single surfactant-laden rising bubble. The characteristics of a clean bubble rising in a quiescent liquid are governed by nondimensional numbers, i.e., the Galileo number , which compares inertial and viscous effects, and the Bond number , which compares gravitational and surface tension stresses. The effect of insoluble surfactants introduces an additional independent parameter, the Marangoni number , comparing the change in surface tension forces due to gradients in surfactants concentration with viscous forces. We apply our numerical methods to investigate the influence of surfactants (through the Marangoni number) on rising bubbles in otherwise quiescent fluids. We observe that an increase in the Marangoni number first decreases the rise velocity before reaching a limiting value at high . The value of necessary to observe a significant slowdown increases with . We discuss the associated surfactant accumulation and the vortical dynamics when a steady state is reached. Finally, we perform three-dimensional simulations and demonstrate that Marangoni effects can induce a change in the rise trajectory from spiraling to zigzagging for set values of Bo and Ga, consistent with experimental results.
需要改进数值方法来了解表面活性剂在界面流体力学中的影响，其应用领域包括薄膜、喷墨打印和海洋-大气相互作用。我们提供了一种三维耦合流体体积（VoF）和相场数值方法，用于模拟含有不溶性表面活性剂的流动的影响。根据表面活性剂传输和马兰戈尼应力的分析案例对该框架进行了验证。然后，我们系统地研究了单个含表面活性剂的上升气泡。在静止液体中上升的清洁气泡的特性受非量纲数的制约，即伽利略数 Ga（比较惯性效应和粘性效应）和邦德数 Bo（比较重力应力和表面张力应力）。不溶性表面活性剂的影响引入了一个额外的独立参数，即马兰戈尼数 Ma，用于比较表面活性剂浓度梯度引起的表面张力变化与粘性力。我们运用数值方法研究了表面活性剂（通过马兰戈尼数）对静止流体中上升气泡的影响。我们观察到，马兰戈尼数的增加首先会降低上升速度，然后在高 Ma 值时达到极限值。我们讨论了相关的表面活性剂积累以及达到稳定状态时的涡旋动力学。最后，我们进行了三维模拟，并证明马兰戈尼效应可以诱导上升轨迹从螺旋上升到设定 Bo 和 Ga 值的之字形上升，这与实验结果一致。
{"title":"Coupled volume of fluid and phase field method for direct numerical simulation of insoluble surfactant-laden interfacial flows and application to rising bubbles","authors":"Palas Kumar Farsoiya, Stéphane Popinet, Howard A. Stone, Luc Deike","doi":"10.1103/physrevfluids.9.094004","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.094004","url":null,"abstract":"Improved numerical methods are needed to understand the effect of surfactants in interfacial fluid mechanics, with various applications including thin films, inkjet printing, and ocean-atmosphere interactions. We provide a three-dimensional coupled volume of fluid (VoF) and phase field numerical approach to simulate the effects of insoluble surfactant-laden flows. The framework is validated against analytical cases for surfactant transport and Marangoni stresses. We then systematically investigate a single surfactant-laden rising bubble. The characteristics of a clean bubble rising in a quiescent liquid are governed by nondimensional numbers, i.e., the Galileo number <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mtext>Ga</mtext></math>, which compares inertial and viscous effects, and the Bond number <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mtext>Bo</mtext></math>, which compares gravitational and surface tension stresses. The effect of insoluble surfactants introduces an additional independent parameter, the Marangoni number <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mtext>Ma</mtext></math>, comparing the change in surface tension forces due to gradients in surfactants concentration with viscous forces. We apply our numerical methods to investigate the influence of surfactants (through the Marangoni number) on rising bubbles in otherwise quiescent fluids. We observe that an increase in the Marangoni number first decreases the rise velocity before reaching a limiting value at high <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mtext>Ma</mtext></math>. The value of <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mtext>Ma</mtext></math> necessary to observe a significant slowdown increases with <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mtext>Ga</mtext></math>. We discuss the associated surfactant accumulation and the vortical dynamics when a steady state is reached. Finally, we perform three-dimensional simulations and demonstrate that Marangoni effects can induce a change in the rise trajectory from spiraling to zigzagging for set values of Bo and Ga, consistent with experimental results.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"32 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142227825","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-13DOI: 10.1103/physrevfluids.9.094604
Sukhdev Mouraya, Nandita Pan, Supratik Banerjee
The nonlinear transfer rate of the total energy (transfer rate of kinetic energy transfer rate due to the work done by the magnetization) for an incompressible turbulent ferrofluid system is studied under the assumption of statistical homogeneity. Using the formalism of the two-point correlators, an exact relation connecting the second-order statistical moments to the average energy injection rate is derived for the scale-to-scale transfer of the total energy. We validate the universality of the exact relation through direct numerical simulations for stationary and nonstationary cascade regimes. For a weak external magnetic field, both kinetic and the total energy cascade with nearly the same cascade rate. A stationary cascade regime is achieved, and hence a good agreement between the exact energy transfer rate and the average energy injection is found. Due to the rapid alignment of the ferrofluid particles in the presence of strong external fields, the turbulence dynamics becomes nonstationary. Interestingly, there too, both kinetic and the total energy exhibit inertial range cascades but with different cascade rates which can be explained using the nonstationary form of our derived exact relation.
{"title":"Stationary and nonstationary energy cascades in homogeneous ferrofluid turbulence","authors":"Sukhdev Mouraya, Nandita Pan, Supratik Banerjee","doi":"10.1103/physrevfluids.9.094604","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.094604","url":null,"abstract":"The nonlinear transfer rate of the total energy (transfer rate of kinetic energy <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mo>+</mo></math> transfer rate due to the work done by the magnetization) for an incompressible turbulent ferrofluid system is studied under the assumption of statistical homogeneity. Using the formalism of the two-point correlators, an exact relation connecting the second-order statistical moments to the average energy injection rate is derived for the scale-to-scale transfer of the total energy. We validate the universality of the exact relation through direct numerical simulations for stationary and nonstationary cascade regimes. For a weak external magnetic field, both kinetic and the total energy cascade with nearly the same cascade rate. A stationary cascade regime is achieved, and hence a good agreement between the exact energy transfer rate and the average energy injection is found. Due to the rapid alignment of the ferrofluid particles in the presence of strong external fields, the turbulence dynamics becomes nonstationary. Interestingly, there too, both kinetic and the total energy exhibit inertial range cascades but with different cascade rates which can be explained using the nonstationary form of our derived exact relation.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"49 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142210889","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-13DOI: 10.1103/physrevfluids.9.094605
A. Mohamed, A. Delache, F. S. Godeferd, J. Liu, M. Oberlack, Y. Wang
We study the propagation of inertial waves (IWs) generated by an axisymmetric torus oscillating at frequency in a rotating fluid. Inertial waves are emitted from the torus and propagate at an angle that depends on the ratio of the rotation frequency of the fluid to the forcing frequency of the torus. The waves focus in a neighborhood of the apex of the propagation cone. Using direct numerical simulations, we characterize the flow in this region, within a linear approximation or in the regime where nonlinear interactions between waves produce a turbulent patch. Forcing by the torus is modeled in two ways. The first model represents the effect of the oscillating torus as a local volume force in the form of a Dirac delta function, called the Dirac ring. The second approach aims at a more realistic three-dimensional model of a torus represented by a volume penalization technique. We observe the appearance of a mean flow composed of a central vortex produced by the nonlinear interaction of the IWs. We show that this phenomenon is in agreement with the theory of Davidson et al. [J. Fluid Mech.557, 135 (2006)] for a rotating fluid. Using Dirac ring forcing in the linear regime, we obtain the dependence on the propagation angle of the vertical kinetic energy at the focal point, which reaches a maximum for , in agreement with the linear theory developed by Liu et al. [Phys. Fluids34, 086601 (2022)]. A similar angle is observed in the 3D torus forcing case for both linear and nonlinear simulations: the angle maximizes the vertical velocity and dissipation, attesting an optimal energy transfer from the oscillating source to the focal region. In the nonlinear regime, we obtain the detailed spectral distribution of the kinetic energy in the focal zone, and we develop a spatiotemporal analysis of the velocity field that shows a wide presence of IWs in the flow. Moreover, we identify triadic resonances of IWs that lead to the production of the turbulent patch and of a large-scale mode similar to the geostrophic mean flow.
{"title":"Maximization of inertial waves focusing in linear and nonlinear regimes","authors":"A. Mohamed, A. Delache, F. S. Godeferd, J. Liu, M. Oberlack, Y. Wang","doi":"10.1103/physrevfluids.9.094605","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.094605","url":null,"abstract":"We study the propagation of inertial waves (IWs) generated by an axisymmetric torus oscillating at frequency <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>ω</mi><mi>f</mi></msub></math> in a rotating fluid. Inertial waves are emitted from the torus and propagate at an angle <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>θ</mi><mi>f</mi></msub></math> that depends on the ratio of the rotation frequency of the fluid to the forcing frequency of the torus. The waves focus in a neighborhood of the apex of the propagation cone. Using direct numerical simulations, we characterize the flow in this region, within a linear approximation or in the regime where nonlinear interactions between waves produce a turbulent patch. Forcing by the torus is modeled in two ways. The first model represents the effect of the oscillating torus as a local volume force in the form of a Dirac delta function, called the Dirac ring. The second approach aims at a more realistic three-dimensional model of a torus represented by a volume penalization technique. We observe the appearance of a mean flow composed of a central vortex produced by the nonlinear interaction of the IWs. We show that this phenomenon is in agreement with the theory of Davidson <i>et al.</i> [<span>J. Fluid Mech.</span> <b>557</b>, 135 (2006)] for a rotating fluid. Using Dirac ring forcing in the linear regime, we obtain the dependence on the propagation angle of the vertical kinetic energy at the focal point, which reaches a maximum for <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><msub><mi>θ</mi><mi>f</mi></msub><mo>=</mo><msup><mn>35</mn><mo>∘</mo></msup></mrow></math>, in agreement with the linear theory developed by Liu <i>et al.</i> [<span>Phys. Fluids</span> <b>34</b>, 086601 (2022)]. A similar angle is observed in the 3D torus forcing case for both linear and nonlinear simulations: the angle <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><msub><mi>θ</mi><mi>f</mi></msub><mo>=</mo><msup><mn>30</mn><mo>∘</mo></msup></mrow></math> maximizes the vertical velocity and dissipation, attesting an optimal energy transfer from the oscillating source to the focal region. In the nonlinear regime, we obtain the detailed spectral distribution of the kinetic energy in the focal zone, and we develop a spatiotemporal analysis of the velocity field that shows a wide presence of IWs in the flow. Moreover, we identify triadic resonances of IWs that lead to the production of the turbulent patch and of a large-scale mode similar to the geostrophic mean flow.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"6 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142210879","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-12DOI: 10.1103/physrevfluids.9.094003
Chunheng Zhao, Taehun Lee, Andreas Carlson
We use the conservative phase-field lattice Boltzmann method to investigate the dynamics when a Newtonian droplet comes in contact with an immiscible viscoelastic liquid film. The dynamics of the three liquid phases are explored through numerical simulations, with a focus on illustrating the contact line dynamics and the viscoelastic effects described by the Oldroyd-B model. The droplet dynamics are contrasted with the case of a Newtonian fluid film. The simulations demonstrate that when the film is viscoelastic, the droplet dynamics become insensitive to the film thickness when the polymer viscosity and relaxation time are large. A viscoelastic ridge forms at the moving contact line, which evolves with a power-law dependence on time. By rescaling the interface profile of the ridge using its height and width, it appears to collapse onto a similar shape. Our findings reveal a strong correlation between the viscoelastic stress and the interface shape near the contact line.
{"title":"Spreading and engulfment of a viscoelastic film onto a Newtonian droplet","authors":"Chunheng Zhao, Taehun Lee, Andreas Carlson","doi":"10.1103/physrevfluids.9.094003","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.094003","url":null,"abstract":"We use the conservative phase-field lattice Boltzmann method to investigate the dynamics when a Newtonian droplet comes in contact with an immiscible viscoelastic liquid film. The dynamics of the three liquid phases are explored through numerical simulations, with a focus on illustrating the contact line dynamics and the viscoelastic effects described by the Oldroyd-B model. The droplet dynamics are contrasted with the case of a Newtonian fluid film. The simulations demonstrate that when the film is viscoelastic, the droplet dynamics become insensitive to the film thickness when the polymer viscosity and relaxation time are large. A viscoelastic ridge forms at the moving contact line, which evolves with a power-law dependence on time. By rescaling the interface profile of the ridge using its height and width, it appears to collapse onto a similar shape. Our findings reveal a strong correlation between the viscoelastic stress and the interface shape near the contact line.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"58 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142210883","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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