Pub Date : 2024-08-01DOI: 10.1103/physrevfluids.9.083601
L. Jørgensen
Drop impact experiments are performed with very viscous fluids to propose a description of the drop deformation at low Reynolds number. We focus on a specific case where dimensionless parameters other than the Reynolds number play no role, which means that only kinetic energy and viscous dissipation determine the final deformation. The same situation in the case of a Reynolds number larger than ten has been clarified years ago. The maximum diameter of the spread drop is well described by a 1/5 power law of the Reynolds number only. Here the deformation of the drop, defined as the contact diameter rescaled by the drop size, is also a power law of the Reynolds number. From experimental data and scaling arguments, the exponent of the power law is shown to be 1/3.
{"title":"Deformation of drops at low Reynolds number impact","authors":"L. Jørgensen","doi":"10.1103/physrevfluids.9.083601","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.083601","url":null,"abstract":"Drop impact experiments are performed with very viscous fluids to propose a description of the drop deformation at low Reynolds number. We focus on a specific case where dimensionless parameters other than the Reynolds number play no role, which means that only kinetic energy and viscous dissipation determine the final deformation. The same situation in the case of a Reynolds number larger than ten has been clarified years ago. The maximum diameter of the spread drop is well described by a 1/5 power law of the Reynolds number only. Here the deformation of the drop, defined as the contact diameter rescaled by the drop size, is also a power law of the Reynolds number. From experimental data and scaling arguments, the exponent of the power law is shown to be 1/3.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"36 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141873093","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 : 2024-08-01DOI: 10.1103/physrevfluids.9.083701
Gunnar G. Peng, Rodolfo Brandão, Ehud Yariv, Ory Schnitzer
We illuminate effects of surface-charge convection intrinsic to leaky-dielectric electrohydrodynamics by analyzing the symmetric steady state of a circular drop in an external field at arbitrary electric Reynolds number <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>Re</mi><mi>E</mi></msub></math>. In formulating the problem, we identify an exact factorization that reduces the number of dimensionless parameters from four—<math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mi>Re</mi><mi>E</mi></msub></math> and the conductivity, permittivity and viscosity ratios—to two: a modified electric Reynolds number <math xmlns="http://www.w3.org/1998/Math/MathML"><mover accent="true"><mi>Re</mi><mo>̃</mo></mover></math> and a charging parameter <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>ϖ</mi></math>. In the case <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>ϖ</mi><mo><</mo><mn>0</mn></mrow></math>, where charge relaxation in the drop phase is slower than in the suspending phase, and, as a consequence, the interface polarizes antiparallel to the external field, we find that above a critical <math xmlns="http://www.w3.org/1998/Math/MathML"><mover accent="true"><mi>Re</mi><mo>̃</mo></mover></math> value the solution exhibits a blowup singularity such that the surface-charge density diverges antisymmetrically with the <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mo>−</mo><mn>1</mn><mo>/</mo><mn>3</mn></mrow></math> power of distance from the equator. We use local analysis to uncover the structure of that blowup singularity, wherein surface charges are convected by a locally induced flow towards the equator where they annihilate. To study the blowup regime, we devise a numerical scheme encoding that local structure where the blowup prefactor is determined by a global charging-annihilation balance. We also employ asymptotic analysis to construct a universal problem governing the blowup solutions in the regime <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mover accent="true"><mi>Re</mi><mo>̃</mo></mover><mo>≫</mo><mn>1</mn></mrow></math>, far beyond the blowup threshold. In the case <math xmlns="http://www.w3.org/1998/Math/MathML"><mrow><mi>ϖ</mi><mo>></mo><mn>0</mn></mrow></math>, where charge relaxation is faster in the drop phase and the interface polarizes parallel to the external field, we numerically observe and asymptotically characterize the formation at large <math xmlns="http://www.w3.org/1998/Math/MathML"><mover accent="true"><mi>Re</mi><mo>̃</mo></mover></math> of stagnant, perfectly conducting surface-charge caps about the drop poles. The cap size grows and the cap voltage decreases monotonically with increasing conductivity or decreasing permittivity of the drop phase relative to the suspending phase. The flow in this scenario is nonlinearly driven by electrical shear stresses at the complement of the caps. In both polarization scenarios, the flow at large <math xmlns="http://www.w3.o
{"title":"Equatorial blowup and polar caps in drop electrohydrodynamics","authors":"Gunnar G. Peng, Rodolfo Brandão, Ehud Yariv, Ory Schnitzer","doi":"10.1103/physrevfluids.9.083701","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.083701","url":null,"abstract":"We illuminate effects of surface-charge convection intrinsic to leaky-dielectric electrohydrodynamics by analyzing the symmetric steady state of a circular drop in an external field at arbitrary electric Reynolds number <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>Re</mi><mi>E</mi></msub></math>. In formulating the problem, we identify an exact factorization that reduces the number of dimensionless parameters from four—<math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>Re</mi><mi>E</mi></msub></math> and the conductivity, permittivity and viscosity ratios—to two: a modified electric Reynolds number <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mover accent=\"true\"><mi>Re</mi><mo>̃</mo></mover></math> and a charging parameter <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>ϖ</mi></math>. In the case <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mi>ϖ</mi><mo><</mo><mn>0</mn></mrow></math>, where charge relaxation in the drop phase is slower than in the suspending phase, and, as a consequence, the interface polarizes antiparallel to the external field, we find that above a critical <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mover accent=\"true\"><mi>Re</mi><mo>̃</mo></mover></math> value the solution exhibits a blowup singularity such that the surface-charge density diverges antisymmetrically with the <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mo>−</mo><mn>1</mn><mo>/</mo><mn>3</mn></mrow></math> power of distance from the equator. We use local analysis to uncover the structure of that blowup singularity, wherein surface charges are convected by a locally induced flow towards the equator where they annihilate. To study the blowup regime, we devise a numerical scheme encoding that local structure where the blowup prefactor is determined by a global charging-annihilation balance. We also employ asymptotic analysis to construct a universal problem governing the blowup solutions in the regime <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mover accent=\"true\"><mi>Re</mi><mo>̃</mo></mover><mo>≫</mo><mn>1</mn></mrow></math>, far beyond the blowup threshold. In the case <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mi>ϖ</mi><mo>></mo><mn>0</mn></mrow></math>, where charge relaxation is faster in the drop phase and the interface polarizes parallel to the external field, we numerically observe and asymptotically characterize the formation at large <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mover accent=\"true\"><mi>Re</mi><mo>̃</mo></mover></math> of stagnant, perfectly conducting surface-charge caps about the drop poles. The cap size grows and the cap voltage decreases monotonically with increasing conductivity or decreasing permittivity of the drop phase relative to the suspending phase. The flow in this scenario is nonlinearly driven by electrical shear stresses at the complement of the caps. In both polarization scenarios, the flow at large <math xmlns=\"http://www.w3.o","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"212 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141869061","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 : 2024-08-01DOI: 10.1103/physrevfluids.9.084001
Konstantinos Papatryfonos, Louis Vervoort, André Nachbin, Matthieu Labousse, John W. M. Bush
Since its discovery in 2005, the hydrodynamic pilot-wave system has provided a concrete macroscopic realization of wave-particle duality and concomitant classical analogs of a growing number of quantum effects. The question naturally arises as to how closely particle-particle correlations achieved with this classical system can mimic those arising on the quantum scale. We here introduce a new platform for addressing this question, a numerical model of cooperative tunneling in a bipartite pilot-wave hydrodynamic system. We execute a static Bell test, in which the system geometry is fixed and the two subsystems are coupled through the intervening wave field. This wave-mediated coupling is not congruent with the assumptions made in deriving Bell's inequality, and so allows one to rationalize the reported violations. Nevertheless, these violations are elusive, and arise only in a limited corner of parameter space.
{"title":"Static Bell test in pilot-wave hydrodynamics","authors":"Konstantinos Papatryfonos, Louis Vervoort, André Nachbin, Matthieu Labousse, John W. M. Bush","doi":"10.1103/physrevfluids.9.084001","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.084001","url":null,"abstract":"Since its discovery in 2005, the hydrodynamic pilot-wave system has provided a concrete macroscopic realization of wave-particle duality and concomitant classical analogs of a growing number of quantum effects. The question naturally arises as to how closely particle-particle correlations achieved with this classical system can mimic those arising on the quantum scale. We here introduce a new platform for addressing this question, a numerical model of cooperative tunneling in a bipartite pilot-wave hydrodynamic system. We execute a static Bell test, in which the system geometry is fixed and the two subsystems are coupled through the intervening wave field. This wave-mediated coupling is not congruent with the assumptions made in deriving Bell's inequality, and so allows one to rationalize the reported violations. Nevertheless, these violations are elusive, and arise only in a limited corner of parameter space.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"46 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141869115","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 : 2024-08-01DOI: 10.1103/physrevfluids.9.084002
Arnab Choudhury, Arghya Samanta
We examine the linear thermocapillary instability of a two-dimensional gravity-driven shear-imposed incompressible viscous film flowing over a uniformly heated inclined wall when the film surface is covered by an insoluble surfactant. The aim is to expand the prior research [Wei, Phys. Fluids17, 012103 (2005)] to the case of a nonisothermal viscous film. As a result, the energy equation is incorporated into the governing equations along with the mass conservation and momentum equations. In the present study, we have found two additional thermocapillary S- and P-modes in the low to moderate Reynolds number regime, along with the known H-mode (surface mode) and surfactant mode. The long-wave analysis predicts that the surfactant Marangoni number, which measures the surface tension gradient due to a change in insoluble surfactant concentration, has a stabilizing impact on the H-mode, but the thermal Marangoni number, which measures the surface tension gradient due to a change in temperature, has a destabilizing impact. These opposing effects produce an analytical relationship between them for which the critical Reynolds number for the H-mode instability of the nonisothermal film flow coincides with that of the isothermal film flow. On the other hand, the numerical result exhibits that the surfactant Marangoni number has a stabilizing influence on the thermocapillary S-mode and P-mode. More specifically, these thermocapillary instabilities diminish with an increase in the value of the surfactant Marangoni number. However, these thermocapillary instabilities can be made stronger by increasing the value of the thermal Marangoni number. Furthermore, the thermal Marangoni number destabilizes the surfactant mode instability, but the onset of instability is not affected in the presence of the thermal Marangoni number, which is in contrast to the influence of the surfactant Marangoni number on the onset of surfactant mode instability. Interestingly, the Biot number, which measures the ratio of heat convection and heat conduction, shows a dual role in the surfactant mode instability, even though the threshold of instability remains the same. In the high Reynolds number regime, the shear mode appears and is stabilized by the surfactant Marangoni number but destabilized by the thermal Marangoni number. Moreover, the comparison of results with inertia and without inertia exhibits a stabilizing role of inertia in the surfactant mode.
我们研究了当薄膜表面被不溶表面活性剂覆盖时，二维重力驱动剪切不可压缩粘性薄膜流过均匀加热斜壁时的线性热毛细管不稳定性。目的是将先前的研究[Wei，Phys. Fluids 17, 012103 (2005)]扩展到非等温粘性薄膜的情况。因此，能量方程与质量守恒和动量方程一起被纳入了控制方程。在本研究中，除了已知的 H 模式（表面模式）和表面活性剂模式之外，我们还发现了在低到中等雷诺数条件下的两种额外的热毛细管 S 模式和 P 模式。长波分析预测，表面活性剂马兰戈尼数（用于测量因不溶性表面活性剂浓度变化而产生的表面张力梯度）对 H 模式有稳定作用，而热马兰戈尼数（用于测量因温度变化而产生的表面张力梯度）则有破坏作用。这些相反的影响在它们之间产生了一种分析关系，即非等温膜流 H 模式不稳定的临界雷诺数与等温膜流的临界雷诺数相吻合。另一方面，数值结果表明，表面活性剂马兰戈尼数对热毛细管 S 模式和 P 模式具有稳定影响。更具体地说，这些热毛细管不稳定性随着表面活性剂马兰戈尼数的增加而减弱。然而，这些热毛细管不稳定性会随着热马兰戈尼数的增加而增强。此外，热马兰戈尼数会破坏表面活性剂模式不稳定性，但在存在热马兰戈尼数的情况下，不稳定性的发生并不受影响，这与表面活性剂马兰戈尼数对表面活性剂模式不稳定性发生的影响形成了鲜明对比。有趣的是，衡量热对流和热传导比率的比奥特数在表面活化剂模式不稳定性中显示出双重作用，尽管不稳定性阈值保持不变。在高雷诺数条件下，剪切模式出现，并通过表面活性剂马兰戈尼数而稳定，但通过热马兰戈尼数而失稳。此外，有惯性和无惯性结果的比较表明，惯性对表面活性剂模式起稳定作用。
{"title":"Thermocapillary instability of a surfactant-laden shear-imposed film flow","authors":"Arnab Choudhury, Arghya Samanta","doi":"10.1103/physrevfluids.9.084002","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.084002","url":null,"abstract":"We examine the linear thermocapillary instability of a two-dimensional gravity-driven shear-imposed incompressible viscous film flowing over a uniformly heated inclined wall when the film surface is covered by an insoluble surfactant. The aim is to expand the prior research [Wei, <span>Phys. Fluids</span> <b>17</b>, 012103 (2005)] to the case of a nonisothermal viscous film. As a result, the energy equation is incorporated into the governing equations along with the mass conservation and momentum equations. In the present study, we have found two additional thermocapillary S- and P-modes in the low to moderate Reynolds number regime, along with the known H-mode (surface mode) and surfactant mode. The long-wave analysis predicts that the surfactant Marangoni number, which measures the surface tension gradient due to a change in insoluble surfactant concentration, has a stabilizing impact on the H-mode, but the thermal Marangoni number, which measures the surface tension gradient due to a change in temperature, has a destabilizing impact. These opposing effects produce an analytical relationship between them for which the critical Reynolds number for the H-mode instability of the nonisothermal film flow coincides with that of the isothermal film flow. On the other hand, the numerical result exhibits that the surfactant Marangoni number has a stabilizing influence on the thermocapillary S-mode and P-mode. More specifically, these thermocapillary instabilities diminish with an increase in the value of the surfactant Marangoni number. However, these thermocapillary instabilities can be made stronger by increasing the value of the thermal Marangoni number. Furthermore, the thermal Marangoni number destabilizes the surfactant mode instability, but the onset of instability is not affected in the presence of the thermal Marangoni number, which is in contrast to the influence of the surfactant Marangoni number on the onset of surfactant mode instability. Interestingly, the Biot number, which measures the ratio of heat convection and heat conduction, shows a dual role in the surfactant mode instability, even though the threshold of instability remains the same. In the high Reynolds number regime, the shear mode appears and is stabilized by the surfactant Marangoni number but destabilized by the thermal Marangoni number. Moreover, the comparison of results with inertia and without inertia exhibits a stabilizing role of inertia in the surfactant mode.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"77 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141869062","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 : 2024-07-31DOI: 10.1103/physrevfluids.9.073401
Ximeng Hou, Dehao Xu, Jianchun Wang, Shiyi Chen
The second moment correlations between thermodynamic fluctuations in incident shock wave/turbulent boundary layer interaction flows at Mach 2.25 are systematically investigated by direct numerical simulation. The concerned fluctuations are those of pressure, entropy, temperature, and density . Effects of wall temperature and Reynolds number are studied. Kovásznay decomposition is introduced to decompose the fluctuations into acoustic and entropic modes. It is shown that all the six concerned correlations are determined by merely two parameters, which are interpreted as intermodal competition and intermodal correlation, respectively. Accordingly, the flow field is divided into several zones, each with distinct physical properties, to analyze the contributing factors to the correlations. In addition, a model is proposed where the correlations are deemed as functions of the root-mean-square values of thermodynamic fluctuations, as in Gerolymos and Vallet [J. Fluid Mech.851, 447 (2018)] but simpler. The formula for each correlation has the same form. The accuracy of the model is validated in boundary layers where the intermodal correlation is weak.
{"title":"Correlations between thermodynamic fluctuations in shock wave/turbulent boundary layer interaction","authors":"Ximeng Hou, Dehao Xu, Jianchun Wang, Shiyi Chen","doi":"10.1103/physrevfluids.9.073401","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.073401","url":null,"abstract":"The second moment correlations between thermodynamic fluctuations in incident shock wave/turbulent boundary layer interaction flows at Mach 2.25 are systematically investigated by direct numerical simulation. The concerned fluctuations are those of pressure, entropy, temperature, and density <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mo>{</mo><msup><mi>p</mi><mo>′</mo></msup><mo>,</mo><msup><mi>s</mi><mo>′</mo></msup><mo>,</mo><msup><mi>T</mi><mo>′</mo></msup><mo>,</mo><msup><mi>ρ</mi><mo>′</mo></msup><mo>}</mo></mrow></math>. Effects of wall temperature and Reynolds number are studied. Kovásznay decomposition is introduced to decompose the fluctuations into acoustic and entropic modes. It is shown that all the six concerned correlations are determined by merely two parameters, which are interpreted as intermodal competition and intermodal correlation, respectively. Accordingly, the flow field is divided into several zones, each with distinct physical properties, to analyze the contributing factors to the correlations. In addition, a model is proposed where the correlations are deemed as functions of the root-mean-square values of thermodynamic fluctuations, as in Gerolymos and Vallet [<span>J. Fluid Mech.</span> <b>851</b>, 447 (2018)] but simpler. The formula for each correlation has the same form. The accuracy of the model is validated in boundary layers where the intermodal correlation is weak.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"44 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141869114","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 : 2024-07-31DOI: 10.1103/physrevfluids.9.074103
Jian Teng, Sungwon La, Jesse T. Ault
A parallel-plate rotational rheometer measures the viscosity of a fluid by rotating the top plate relative to the bottom plate in order to induce a shear on the fluid and measuring the torques and forces that result as a function of the induced rotation rate. Manufacturing imperfections can often lead to unintentional misalignment of the plates of the rheometer, where the top and bottom plates are not perfectly parallel, and this misalignment can affect the fluid dynamics inside the rheometer. This study examines the effect that misalignment has on the viscosity measurements of Newtonian fluids in the limit of small rheometer gap heights. A theoretical model for the behavior of a general Newtonian fluid in a misaligned rheometer with a small gap height is derived using perturbation expansions. The theoretical results show that at small gap heights, misalignment can produce additional secondary velocity components and pressures in the fluid, which affect the forces and moments in the rheometer. In such cases at small Reynolds numbers, the dominant forces and moments acting on the top plate of the rheometer are the viscous force in the direction parallel to the tilt axis, the pressure moment in the direction perpendicular to the tilt axis and in the cross-sectional plane, and the viscous moment in the direction along the height of the rheometer. These forces and moments on the top plate were found to increase as the misalignment tilt angle increased, leading to an increase in the error of viscosity measurement by the rheometer. Three-dimensional numerical simulations validate the theoretical predictions.
{"title":"Newtonian fluid dynamics in a misaligned parallel-plate rheometer","authors":"Jian Teng, Sungwon La, Jesse T. Ault","doi":"10.1103/physrevfluids.9.074103","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.074103","url":null,"abstract":"A parallel-plate rotational rheometer measures the viscosity of a fluid by rotating the top plate relative to the bottom plate in order to induce a shear on the fluid and measuring the torques and forces that result as a function of the induced rotation rate. Manufacturing imperfections can often lead to unintentional misalignment of the plates of the rheometer, where the top and bottom plates are not perfectly parallel, and this misalignment can affect the fluid dynamics inside the rheometer. This study examines the effect that misalignment has on the viscosity measurements of Newtonian fluids in the limit of small rheometer gap heights. A theoretical model for the behavior of a general Newtonian fluid in a misaligned rheometer with a small gap height is derived using perturbation expansions. The theoretical results show that at small gap heights, misalignment can produce additional secondary velocity components and pressures in the fluid, which affect the forces and moments in the rheometer. In such cases at small Reynolds numbers, the dominant forces and moments acting on the top plate of the rheometer are the viscous force in the direction parallel to the tilt axis, the pressure moment in the direction perpendicular to the tilt axis and in the cross-sectional plane, and the viscous moment in the direction along the height of the rheometer. These forces and moments on the top plate were found to increase as the misalignment tilt angle increased, leading to an increase in the error of viscosity measurement by the rheometer. Three-dimensional numerical simulations validate the theoretical predictions.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"49 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141869066","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 : 2024-07-29DOI: 10.1103/physrevfluids.9.l072301
M. Crialesi-Esposito, G. Boffetta, L. Brandt, S. Chibbaro, S. Musacchio
The formation of small droplets and bubbles in turbulent flows is a crucial process in geophysics and engineering, whose underlying physical mechanism remains a puzzle. In this Letter, we address this problem by means of high-resolution numerical simulations, comparing a realistic multiphase configuration with a numerical experiment in which we attenuate the presence of strong velocity gradients either across the whole mixture or in the disperse phase only. Our results show unambiguously that the formation of small droplets is governed by the internal dynamics which occurs during the breakup of large drops and that the high vorticity and the extreme dissipation associated to these events are the consequence and not the cause of the breakup.
{"title":"How small droplets form in turbulent multiphase flows","authors":"M. Crialesi-Esposito, G. Boffetta, L. Brandt, S. Chibbaro, S. Musacchio","doi":"10.1103/physrevfluids.9.l072301","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.l072301","url":null,"abstract":"The formation of small droplets and bubbles in turbulent flows is a crucial process in geophysics and engineering, whose underlying physical mechanism remains a puzzle. In this Letter, we address this problem by means of high-resolution numerical simulations, comparing a realistic multiphase configuration with a numerical experiment in which we attenuate the presence of strong velocity gradients either across the whole mixture or in the disperse phase only. Our results show unambiguously that the formation of small droplets is governed by the internal dynamics which occurs during the breakup of large drops and that the high vorticity and the extreme dissipation associated to these events are the consequence and not the cause of the breakup.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"46 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-07-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141869065","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 : 2024-07-29DOI: 10.1103/physrevfluids.9.073903
Antoine Jouin, Jean-Christophe Robinet, Stefania Cherubini
Modal and nonmodal stability analysis of a channel flow with longitudinal riblets are investigated. To this extent, a method based on the coupling between a two-dimensional stability problem and a computational framework for -periodic systems based on Bloch waves is proposed. Unstable modes from linear stability can be retrieved. The influence of the riblets on the most amplified flow structures is investigated through a transient growth analysis: a resonance is found when the riblet wavenumber is equal to the wavenumber of the optimal streaks in a smooth channel flow. For large riblet spacing, a wavenumber lock-in regime, in which the streaks dynamics and wavelength are totally controlled by the riblet spacing, is observed. Physically, a modulation of the streaks amplitude in the spanwise direction via a beating mechanism is seen. These phenomena are characteristic of dynamic systems spatially forced and may exhibit geometric frustration. Similar results were found in the study of secondary flows in Rayleigh-Bénard convection with wavy walls. A resolvent analysis is also performed: it is found that riblets lead to the development of oblique waves that may trigger an early transition.
研究了具有纵向波纹的渠道流的模态和非模态稳定性分析。为此，提出了一种基于二维稳定性问题与基于布洛赫波的 n 周期系统计算框架之间耦合的方法。可以从线性稳定性中检索出不稳定模式。通过瞬态增长分析研究了波纹对最放大流动结构的影响：当波纹的波数等于平滑通道流中最佳条纹的波数时，就会产生共振。在波纹间距较大的情况下，会观察到一个波长锁定机制，其中条纹的动态和波长完全由波纹间距控制。从物理角度看，条纹振幅在跨度方向上通过跳动机制进行调制。这些现象是空间受迫动态系统的特征，可能表现出几何挫折。在研究具有波浪壁的雷利-贝纳德对流中的二次流时也发现了类似的结果。还进行了解析分析：发现波纹导致斜波的发展，可能引发早期过渡。
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Pub Date : 2024-07-29DOI: 10.1103/physrevfluids.9.l071101
Midhun Puthumana Melepattu, Guillaume Maîtrejean, Thomas Podgorski
Blood rheology and microcirculation are strongly influenced by red blood cell aggregation. We investigate the dissociation rates of red cell aggregates in extensional flow using hyperbolic microfluidic constrictions and image analysis by a convolutional neural network (CNN). Our findings reveal that aggregate dissociation increases sharply when a critical extension rate is reached which falls within the range of microcirculatory conditions, suggesting that large variations of aggregate sizes should be expected in vivo. This work contributes to a deeper understanding of the behavior of red blood cell aggregates in response to extensional stress in microcirculatory networks, provides crucial experimental data to validate theoretical and numerical models, and constitutes the basis for improved evaluation of blood aggregability in clinical contexts.
{"title":"Dissociation of red blood cell aggregates in extensional flow","authors":"Midhun Puthumana Melepattu, Guillaume Maîtrejean, Thomas Podgorski","doi":"10.1103/physrevfluids.9.l071101","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.l071101","url":null,"abstract":"Blood rheology and microcirculation are strongly influenced by red blood cell aggregation. We investigate the dissociation rates of red cell aggregates in extensional flow using hyperbolic microfluidic constrictions and image analysis by a convolutional neural network (CNN). Our findings reveal that aggregate dissociation increases sharply when a critical extension rate is reached which falls within the range of microcirculatory conditions, suggesting that large variations of aggregate sizes should be expected <i>in vivo</i>. This work contributes to a deeper understanding of the behavior of red blood cell aggregates in response to extensional stress in microcirculatory networks, provides crucial experimental data to validate theoretical and numerical models, and constitutes the basis for improved evaluation of blood aggregability in clinical contexts.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"13 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-07-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141869063","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 : 2024-07-26DOI: 10.1103/physrevfluids.9.074201
Shubhra Sahu, Bapan Mondal, Somnath Bhattacharyya
Atomistic and coarse-grained simulations show the formation of a condensed layer of counterions near a charged surface in contact with multivalent or monovalent electrolytes of high concentration. This condensed layer may overscreen the surface charge, and eventually a coion-dominated region may arise within the electric double layer, which again draws a layer of counterions and so on till the charge density approaches zero. Such a type of overscreening and charge density oscillation cannot be predicted through the mean-field based models as it does not account for the correlations between discrete charges. In the present study the mean-field-based model has been extended to consider the many-body interactions to analyze the electro-osmosis and ion transport of multivalent electrolytes in a highly charged nanopore. The ions are considered to be finite-sized, which is accounted for by considering the hydrodynamic steric interactions and modification of the suspension medium viscosity. Consideration of the electrostatic correlation leads to a fourth-order Poisson-Fermi equation for an electric field. Such a type of continuum model is easy to handle and to use to predict the layered structure of the EDL. Our model captures the existing experimental and molecular dynamics simulation correctly. Based on the modified model, we have analyzed the volume flow rate, current density, and ion selectivity of the pore in multivalent electrolytes for different electrostatic conditions. The present model shows that the counterion size has an impact on the condensed layer and hence overscreening. We demonstrate that the EOF reversal of multivalent electrolytes can be suppressed by mixing with monovalent slats.
{"title":"Ion steric interactions and electrostatic correlations on electro-osmotic flow in charged nanopores with multivalent electrolytes","authors":"Shubhra Sahu, Bapan Mondal, Somnath Bhattacharyya","doi":"10.1103/physrevfluids.9.074201","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.074201","url":null,"abstract":"Atomistic and coarse-grained simulations show the formation of a condensed layer of counterions near a charged surface in contact with multivalent or monovalent electrolytes of high concentration. This condensed layer may overscreen the surface charge, and eventually a coion-dominated region may arise within the electric double layer, which again draws a layer of counterions and so on till the charge density approaches zero. Such a type of overscreening and charge density oscillation cannot be predicted through the mean-field based models as it does not account for the correlations between discrete charges. In the present study the mean-field-based model has been extended to consider the many-body interactions to analyze the electro-osmosis and ion transport of multivalent electrolytes in a highly charged nanopore. The ions are considered to be finite-sized, which is accounted for by considering the hydrodynamic steric interactions and modification of the suspension medium viscosity. Consideration of the electrostatic correlation leads to a fourth-order Poisson-Fermi equation for an electric field. Such a type of continuum model is easy to handle and to use to predict the layered structure of the EDL. Our model captures the existing experimental and molecular dynamics simulation correctly. Based on the modified model, we have analyzed the volume flow rate, current density, and ion selectivity of the pore in multivalent electrolytes for different electrostatic conditions. The present model shows that the counterion size has an impact on the condensed layer and hence overscreening. We demonstrate that the EOF reversal of multivalent electrolytes can be suppressed by mixing with monovalent slats.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"44 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-07-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141775933","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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