Pub Date : 2024-08-09DOI: 10.1103/physrevfluids.9.084003
A. Della Pia, M. Chiatto, L. de Luca
{"title":"Varicose dynamics of liquid curtain: Linear analysis and volume-of-fluid simulations","authors":"A. Della Pia, M. Chiatto, L. de Luca","doi":"10.1103/physrevfluids.9.084003","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.084003","url":null,"abstract":"","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":null,"pages":null},"PeriodicalIF":2.5,"publicationDate":"2024-08-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141921204","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 : 2024-08-09DOI: 10.1103/physrevfluids.9.083202
Peng-jin Yang, Dehai Yu, Zheng Chen, H. Teng, Hoi Dick Ng
{"title":"Effects of thermal stratification on detonation development in hypersonic reactive flows","authors":"Peng-jin Yang, Dehai Yu, Zheng Chen, H. Teng, Hoi Dick Ng","doi":"10.1103/physrevfluids.9.083202","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.083202","url":null,"abstract":"","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":null,"pages":null},"PeriodicalIF":2.5,"publicationDate":"2024-08-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141922294","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 : 2024-08-08DOI: 10.1103/physrevfluids.9.084201
Shiyu Li, Weiwei Cui, Thierry Baasch, Bin Wang, Zhixiong Gong
Acoustic streaming shows great potential in applications such as bubble dynamics, cell aggregation, and nanosized particle isolation in the biomedical and drug industries. As the acoustic shock distance decreases with the increase of incident frequency, the nonlinear propagation effect will play a role in acoustic streaming, e.g., Eckart (bulk) streaming at a few gigahertz. However, the theory of source terms of bulk streaming is still missing at this stage when high-order acoustic harmonics play a role. In this paper, we derive the source term including the contribution of high-order harmonics. The streaming-induced hydrodynamic flow is assumed to be incompressible and no shock wave occurs during the nonlinear acoustic propagation as restricted by the traditional Goldberg number or , which indicates the importance of nonlinearity relative to dissipation. The derived force terms allow evaluating bulk streaming with high-order harmonics at gigahertz and provide an exact expression compared to the existing empirical formulas. Numerical results show that the contribution of higher-order harmonics increases the streaming flow velocity by more than . Our approach clearly demonstrates the errors inherent in the expression introduced by Nyborg which should be avoided in numerical computations as it includes part of the acoustic radiation force that does not lead to acoustic streaming.
{"title":"Eckart streaming with nonlinear high-order harmonics: An example at gigahertz","authors":"Shiyu Li, Weiwei Cui, Thierry Baasch, Bin Wang, Zhixiong Gong","doi":"10.1103/physrevfluids.9.084201","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.084201","url":null,"abstract":"Acoustic streaming shows great potential in applications such as bubble dynamics, cell aggregation, and nanosized particle isolation in the biomedical and drug industries. As the acoustic shock distance decreases with the increase of incident frequency, the nonlinear propagation effect will play a role in acoustic streaming, e.g., Eckart (bulk) streaming at a few gigahertz. However, the theory of source terms of bulk streaming is still missing at this stage when high-order acoustic harmonics play a role. In this paper, we derive the source term including the contribution of high-order harmonics. The streaming-induced hydrodynamic flow is assumed to be incompressible and no shock wave occurs during the nonlinear acoustic propagation as restricted by the traditional Goldberg number <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mi mathvariant=\"normal\">Γ</mi><mo><</mo><mn>1</mn></mrow></math> or <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mi mathvariant=\"normal\">Γ</mi><mo>≈</mo><mn>1</mn></mrow></math>, which indicates the importance of nonlinearity relative to dissipation. The derived force terms allow evaluating bulk streaming with high-order harmonics at gigahertz and provide an exact expression compared to the existing empirical formulas. Numerical results show that the contribution of higher-order harmonics increases the streaming flow velocity by more than <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mn>20</mn><mo>%</mo></mrow></math>. Our approach clearly demonstrates the errors inherent in the expression introduced by Nyborg which should be avoided in numerical computations as it includes part of the acoustic radiation force that does not lead to acoustic streaming.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-08-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141968949","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 : 2024-08-07DOI: 10.1103/physrevfluids.9.083602
Tobias Bauer, Tristan Gilet
When a drop impacts next to the edge of a solid substrate, it may spread beyond this edge. It then forms a liquid sheet surrounded by a rim from which droplets may be ejected. This work investigates the influence of the edge shape on the rim dynamics and subsequent droplet ejections. Experiments of drop impacts on star-shaped poles are reported. Both the rim and the ejected droplets are tracked. An analytical model is proposed to rationalize the amplitude of rim deformations induced by the edge shape. Statistical distributions of position, size, and velocity of ejected droplets are also shaped by the edge geometry.
{"title":"Rim dynamics and droplet ejections upon drop impact on star-shaped poles","authors":"Tobias Bauer, Tristan Gilet","doi":"10.1103/physrevfluids.9.083602","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.083602","url":null,"abstract":"When a drop impacts next to the edge of a solid substrate, it may spread beyond this edge. It then forms a liquid sheet surrounded by a rim from which droplets may be ejected. This work investigates the influence of the edge shape on the rim dynamics and subsequent droplet ejections. Experiments of drop impacts on star-shaped poles are reported. Both the rim and the ejected droplets are tracked. An analytical model is proposed to rationalize the amplitude of rim deformations induced by the edge shape. Statistical distributions of position, size, and velocity of ejected droplets are also shaped by the edge geometry.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141936214","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 : 2024-08-07DOI: 10.1103/physrevfluids.9.084602
Masato Hirota, Seiichiro Izawa, Yu Fukunishi
A numerical experiment is conducted to investigate the response of a homogeneous isotropic turbulent field at a statistically equilibrium state when the energy cascade process is abruptly interrupted. Vortex motions of a certain scale in the inertial subrange are extracted using a Fourier bandpass filter and forcibly damped by applying artificial forces to the small regions that are the target vortices. Once the forces are applied, the target vortices immediately disappear from the flow field, which is followed by a slight increase in kinetic energy in the larger scale range and a decrease in the smaller scale range. The decrease in energy in the smaller scale range is likely to be caused by the decrease in the stretching speeds of the vortices of that range. Next, the behaviors of individual vortices whose scales are either four times or twice as large as the target scale are tracked using a method in which each vortex is reconstructed as a group of vortex units. It is found that the vortices that are twice as large as the target vortices show smaller curvatures and longer lifespans in comparison to the case without artificial forces, while no remarkable changes are found for the vortices that are four times larger.
{"title":"Response of turbulent energy spectrum and flow structures when vortical motion of a certain scale is suppressed by artificial forcing","authors":"Masato Hirota, Seiichiro Izawa, Yu Fukunishi","doi":"10.1103/physrevfluids.9.084602","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.084602","url":null,"abstract":"A numerical experiment is conducted to investigate the response of a homogeneous isotropic turbulent field at a statistically equilibrium state when the energy cascade process is abruptly interrupted. Vortex motions of a certain scale in the inertial subrange are extracted using a Fourier bandpass filter and forcibly damped by applying artificial forces to the small regions that are the target vortices. Once the forces are applied, the target vortices immediately disappear from the flow field, which is followed by a slight increase in kinetic energy in the larger scale range and a decrease in the smaller scale range. The decrease in energy in the smaller scale range is likely to be caused by the decrease in the stretching speeds of the vortices of that range. Next, the behaviors of individual vortices whose scales are either four times or twice as large as the target scale are tracked using a method in which each vortex is reconstructed as a group of vortex units. It is found that the vortices that are twice as large as the target vortices show smaller curvatures and longer lifespans in comparison to the case without artificial forces, while no remarkable changes are found for the vortices that are four times larger.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141936218","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 : 2024-08-07DOI: 10.1103/physrevfluids.9.l081601
Etienne Jambon-Puillet
Pendant drops spontaneously appear on the underside of wet surfaces through the Rayleigh-Taylor instability. These droplets are connected to a thin liquid film with which they exchange liquid and are thus very mobile. Here, using experiments, numerical simulations, and theory, I show that pendant drops sliding under a slightly tilted wet substrate can get stuck on topographic defects, despite their lack of contact line. Instead, this trapping has a gravito-capillary origin: liquid has to move up or down and the interface has to deform for the drop to pass the defect. I propose a semianalytical model for arbitrary substrate topographies that matches the trapping force observed, without any fitting parameter. I finally demonstrate how to harness this topography induced force to guide pendant drops on complex paths and expect it to be relevant for other contact line free systems.
{"title":"Gravito-capillary trapping of pendant droplets under wet uneven surfaces","authors":"Etienne Jambon-Puillet","doi":"10.1103/physrevfluids.9.l081601","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.l081601","url":null,"abstract":"Pendant drops spontaneously appear on the underside of wet surfaces through the Rayleigh-Taylor instability. These droplets are connected to a thin liquid film with which they exchange liquid and are thus very mobile. Here, using experiments, numerical simulations, and theory, I show that pendant drops sliding under a slightly tilted wet substrate can get stuck on topographic defects, despite their lack of contact line. Instead, this trapping has a gravito-capillary origin: liquid has to move up or down and the interface has to deform for the drop to pass the defect. I propose a semianalytical model for arbitrary substrate topographies that matches the trapping force observed, without any fitting parameter. I finally demonstrate how to harness this topography induced force to guide pendant drops on complex paths and expect it to be relevant for other contact line free systems.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141936217","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 : 2024-08-07DOI: 10.1103/physrevfluids.9.l081101
Cyril Karamaoun, Haribalan Kumar, Médéric Argentina, Didier Clamond, Benjamin Mauroy
The mucus on the bronchial wall forms a thin layer of non-Newtonian fluid, protecting the lungs by capturing inhaled pollutants. Due to the corrugation of its interface with air, this layer is subject to surface tension forces that affect its rheology. This physical system is analyzed using lubrication theory and three-dimensional simulations. We characterize the nonlinear behavior of the mucus and show that surface tension effects can displace overly thick mucus layers in airway bifurcations. This movement can disrupt the mucociliary clearance and break the homogeneity of the layer thickness.
{"title":"Curvature-driven transport of thin Bingham fluid layers in airway bifurcations","authors":"Cyril Karamaoun, Haribalan Kumar, Médéric Argentina, Didier Clamond, Benjamin Mauroy","doi":"10.1103/physrevfluids.9.l081101","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.l081101","url":null,"abstract":"The mucus on the bronchial wall forms a thin layer of non-Newtonian fluid, protecting the lungs by capturing inhaled pollutants. Due to the corrugation of its interface with air, this layer is subject to surface tension forces that affect its rheology. This physical system is analyzed using lubrication theory and three-dimensional simulations. We characterize the nonlinear behavior of the mucus and show that surface tension effects can displace overly thick mucus layers in airway bifurcations. This movement can disrupt the mucociliary clearance and break the homogeneity of the layer thickness.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141936216","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 : 2024-08-05DOI: 10.1103/physrevfluids.9.084601
J. Dey
Distribution of the mean streamwise velocity in a turbulent boundary layer over a flat plate can be represented by the equation , as was widely used in the past; and are the normalized velocity and the wall-normal distance, respectively. However, this -power law is an empirical one. By incorporating either the Reynolds shear stress model of Wei et al. [J. Fluid Mech.969, A3 (2023)], which is in terms of and the (normalized) wall-normal velocity (), or a similar one in the boundary layer equations, it is found that and are related as in the outer region of a flat plate boundary layer; is the flow shape parameter. Along with the distribution of the wall-normal velocity () of Wei et al., the -power law for is obtained by equating the derivative (with respect to ) of with that of . Thus, this empirical power law seems to have a reasonable theoretical basis embedded in it.
平板上湍流边界层的平均流向速度分布可用方程 U∼η1/n 表示，这在过去被广泛使用；U 和 η 分别是归一化速度和壁面法线距离。然而，这个 1/n 次幂定律是一个经验定律。通过将 Wei 等人的雷诺剪应力模型[J. Fluid Mech. 969, A3 (2023)]（以 U 和（归一化）壁面法向速度 (V) 表示）或类似的模型纳入边界层方程，可以发现在平板边界层的外部区域，U 和 V 的关系为 U(H+1)∼V(H-1)；H 是流动形状参数。根据 Wei 等人的壁面法向速度（Vw）分布，将 V 的导数（相对于 η）等同于 Vw 的导数，即可得到 U 的 1/n 次幂律。因此，这一经验幂律似乎具有合理的理论基础。
{"title":"Approximate derivation of the power law for the mean streamwise velocity in a turbulent boundary layer under zero-pressure gradient","authors":"J. Dey","doi":"10.1103/physrevfluids.9.084601","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.084601","url":null,"abstract":"Distribution of the mean streamwise velocity in a turbulent boundary layer over a flat plate can be represented by the equation <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mi>U</mi><mo>∼</mo><msup><mi>η</mi><mrow><mn>1</mn><mo>/</mo><mi>n</mi></mrow></msup></mrow></math>, as was widely used in the past; <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>U</mi></math> and <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>η</mi></math> are the normalized velocity and the wall-normal distance, respectively. However, this <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mn>1</mn><mo>/</mo><mi>n</mi></mrow><mi mathvariant=\"normal\">th</mi></math>-power law is an empirical one. By incorporating either the Reynolds shear stress model of Wei <i>et al.</i> [<span>J. Fluid Mech.</span> <b>969</b>, A3 (2023)], which is in terms of <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>U</mi></math> and the (normalized) wall-normal velocity (<math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>V</mi></math>), or a similar one in the boundary layer equations, it is found that <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>U</mi></math> and <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>V</mi></math> are related as <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><msup><mi>U</mi><mrow><mo>(</mo><mi>H</mi><mo>+</mo><mn>1</mn><mo>)</mo></mrow></msup><mo>∼</mo><mspace width=\"4pt\"></mspace><msup><mi>V</mi><mrow><mo>(</mo><mi>H</mi><mo>−</mo><mn>1</mn><mo>)</mo></mrow></msup></mrow></math> in the outer region of a flat plate boundary layer; <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mi>H</mi></mrow></math> is the flow shape parameter. Along with the distribution of the wall-normal velocity (<math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>V</mi><mi>w</mi></msub></math>) of Wei <i>et al.</i>, the <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mn>1</mn><mo>/</mo><mi>n</mi></mrow><mi mathvariant=\"normal\">th</mi></math>-power law for <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>U</mi></math> is obtained by equating the derivative (with respect to <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>η</mi></math>) of <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>V</mi></math> with that of <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>V</mi><mi>w</mi></msub></math>. Thus, this empirical power law seems to have a reasonable theoretical basis embedded in it.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141936219","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 : 2024-08-05DOI: 10.1103/physrevfluids.9.083101
George T. Fortune, Eric Lauga, Raymond E. Goldstein
The humble Petri dish is perhaps the simplest setting in which to examine the locomotion of swimming organisms, particularly those whose body size is tens of microns to millimeters. The fluid layer in such a container has a bottom no-slip surface and a stress-free upper boundary. It is of fundamental interest to understand the flow fields produced by the elementary and composite singularities of Stokes flow in this geometry. Building on the few particular cases that have previously been considered in the literature, we study here the image systems for the primary singularities of Stokes flow subject to such boundary conditions—the Stokeslet, rotlet, source, rotlet dipole, source dipole, and stresslet—paying particular attention to the far-field behavior. In several key situations, the depth-averaged fluid flow is accurately captured by the solution of an associated Brinkman equation whose screening length is proportional to the depth of the fluid layer. The case of hydrodynamic bound states formed by spinning microswimmers near a no-slip surface, discovered first using the alga Volvox, is reconsidered in the geometry of a Petri dish, where the power-law attractive interaction between microswimmers acquires unusual exponentially screened oscillations.
简陋的培养皿也许是研究游泳生物运动的最简单环境，尤其是那些体型只有几十微米到几毫米的生物。这种容器中的流体层具有底部无滑动表面和上部无应力边界。了解这种几何形状中斯托克斯流的基本奇点和复合奇点所产生的流场具有重要意义。基于以前文献中考虑过的少数特殊情况，我们在此研究了斯托克斯流的初级奇点在这种边界条件下的图像系统--斯托克斯小波、小转子、源、小转子偶极子、源偶极子和应力小波--特别关注远场行为。在几种关键情况下，相关布林克曼方程的筛选长度与流体层深度成正比，该方程的求解可准确捕捉深度平均流体流动。首先利用藻类 Volvox 发现的在无滑动表面附近旋转的微游子形成的流体力学束缚状态，在 Petri 碟的几何形状中被重新考虑，微游子之间的幂律吸引力相互作用获得了不寻常的指数屏蔽振荡。
{"title":"Biophysical fluid dynamics in a Petri dish","authors":"George T. Fortune, Eric Lauga, Raymond E. Goldstein","doi":"10.1103/physrevfluids.9.083101","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.083101","url":null,"abstract":"The humble Petri dish is perhaps the simplest setting in which to examine the locomotion of swimming organisms, particularly those whose body size is tens of microns to millimeters. The fluid layer in such a container has a bottom no-slip surface and a stress-free upper boundary. It is of fundamental interest to understand the flow fields produced by the elementary and composite singularities of Stokes flow in this geometry. Building on the few particular cases that have previously been considered in the literature, we study here the image systems for the primary singularities of Stokes flow subject to such boundary conditions—the Stokeslet, rotlet, source, rotlet dipole, source dipole, and stresslet—paying particular attention to the far-field behavior. In several key situations, the depth-averaged fluid flow is accurately captured by the solution of an associated Brinkman equation whose screening length is proportional to the depth of the fluid layer. The case of hydrodynamic bound states formed by spinning microswimmers near a no-slip surface, discovered first using the alga <i>Volvox</i>, is reconsidered in the geometry of a Petri dish, where the power-law attractive interaction between microswimmers acquires unusual exponentially screened oscillations.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":null,"pages":null},"PeriodicalIF":2.7,"publicationDate":"2024-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141936144","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 : 2024-08-05DOI: 10.1103/physrevfluids.9.083201
Rui Xiong, Yufeng Han, Wei Cao
In thermochemical nonequilibrium processes, both the nonequilibrium between different kinds of internal energy of molecules and the non-Boltzmann (NB) energy state distribution significantly impact the dissociation rate coefficients. The conventional two-temperature (2-T) model fails to accurately portray these effects, especially the NB effect. Consequently, dissociation rate coefficients calculated by the 2-T model are inaccurate in simulating strong thermochemical nonequilibrium flow, resulting in a surface heat flux inconsistent with experimental data. This article investigates the influencing factor of the NB effect on the dissociation rate coefficient using the state-to-state (STS) method during the zero-dimensional heating process of and . Based on this, we develop a fitting formula to precisely correct the NB effect. Furthermore, we propose an improved model by integrating this fitting formula with the single-group linear maximum entropy model, which considers only the effect of nonequilibrium between different kinds of internal energy. This improved model provides an accurate description of thermochemical nonequilibrium on the dissociation rate coefficients. To validate the effectiveness of the improved model, we simulate the nonequilibrium process following a normal shock. The results demonstrate that in strong thermochemical nonequilibrium flow, compared to the 2-T Park model, the maximum and average discrepancies between the translation temperatures calculated by the improved model and those by the STS method are reduced by more than 68% and 82%, respectively. Additionally, the results closely align with experimental data, indicating that the improved model can accurately depict the effect of thermal nonequilibrium on dissociation rate coefficients.
在热化学非平衡过程中，不同种类分子内能之间的非平衡和非波尔兹曼（NB）能态分布都会对解离速率系数产生重大影响。传统的双温（2-T）模型无法准确描述这些效应，尤其是非玻尔兹曼效应。因此，2-T 模型计算出的解离速率系数在模拟强热化学非平衡流动时并不准确，导致表面热通量与实验数据不一致。本文利用状态对状态（STS）方法研究了 N2 和 O2 零维加热过程中 NB 效应对解离速率系数的影响因素。在此基础上，我们建立了一个拟合公式来精确修正 NB 效应。此外，我们还提出了一个改进模型，将该拟合公式与单组线性最大熵模型相结合，该模型只考虑了不同种类内能之间的非平衡效应。这一改进模型准确地描述了热化学非平衡对解离速率系数的影响。为了验证改进模型的有效性，我们模拟了正常冲击后的非平衡过程。结果表明，在强热化学非平衡流动中，与 2-T Park 模型相比，改进模型计算的平移温度与 STS 方法计算的平移温度之间的最大差异和平均差异分别减少了 68% 和 82% 以上。此外，计算结果与实验数据非常吻合，表明改进模型能够准确描述热非平衡态对解离速率系数的影响。
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