Pub Date : 2024-08-13DOI: 10.1103/physrevfluids.9.083603
Mariam Dynar, Hamid Ez-Zahraouy, Chaouqi Misbah, Mehdi Abbasi
Homeostasis plays a critical role in maintaining the delicate balance between preventing excessive bleeding and enabling clot formation during injuries. One pivotal aspect of homeostasis involves the development of platelet clots. In this study, we analyze numerically the behavior of platelet margination as a function of the adhesion energy between red blood cells (RBCs), driven by the presence of plasma proteins. We examine scenarios encompassing both physiological conditions and pathological states, such as those seen in patients with diabetes. Employing a two-dimensional simulation, we utilize rigid particles and a vesicle model to simulate platelets and RBCs, respectively. We employ the lattice Boltzmann method to solve the underlying model equations. We first demonstrate that platelet margination is primarily determined by lift forces and is not notably affected by whether the cells undergo tank-treading (TT) or tumbling (TB) behavior, as often reported. Specifically, we unveil instances where cells exhibit TT or TB behavior, yet their platelet concentration profiles closely resemble each other. Furthermore, we present a striking result concerning the impact of RBC adhesion. In microcirculation the hematocrit is in the range . A moderate adhesion energy (falling within the physiological range) boosts platelet margination in microcirculation. However, this effect becomes small for larger hematocrit encountered in macrocirculation (e.g., ). This boost is more significant for a viscosity contrast (viscosity of cytoplasm over that the suspending fluid) equal to a known value for RBCs, as compared to the case without viscosity contrast. As we increase the adhesion energy (the pathological range), a noteworthy decline in platelet margination is found, albeit that for some flow strength the platelet margination reaches a minimum and increases again at higher adhesion energy. These results can be attributed to a combination of lift generated by the bounding walls and the formation of RBC clusters. Notably, our study sheds light on a critical consequence of excessive adhesion, typically observed in pathological conditions like diabetes mellitus.
{"title":"Platelet margination dynamics in blood flow: The role of lift forces and red blood cells aggregation","authors":"Mariam Dynar, Hamid Ez-Zahraouy, Chaouqi Misbah, Mehdi Abbasi","doi":"10.1103/physrevfluids.9.083603","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.083603","url":null,"abstract":"Homeostasis plays a critical role in maintaining the delicate balance between preventing excessive bleeding and enabling clot formation during injuries. One pivotal aspect of homeostasis involves the development of platelet clots. In this study, we analyze numerically the behavior of platelet margination as a function of the adhesion energy between red blood cells (RBCs), driven by the presence of plasma proteins. We examine scenarios encompassing both physiological conditions and pathological states, such as those seen in patients with diabetes. Employing a two-dimensional simulation, we utilize rigid particles and a vesicle model to simulate platelets and RBCs, respectively. We employ the lattice Boltzmann method to solve the underlying model equations. We first demonstrate that platelet margination is primarily determined by lift forces and is not notably affected by whether the cells undergo tank-treading (TT) or tumbling (TB) behavior, as often reported. Specifically, we unveil instances where cells exhibit TT or TB behavior, yet their platelet concentration profiles closely resemble each other. Furthermore, we present a striking result concerning the impact of RBC adhesion. In microcirculation the hematocrit is in the range <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mn>5</mn><mo>–</mo><mn>20</mn><mo>%</mo></mrow></math>. A moderate adhesion energy (falling within the physiological range) boosts platelet margination in microcirculation. However, this effect becomes small for larger hematocrit encountered in macrocirculation (e.g., <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mn>40</mn><mo>%</mo></mrow></math>). This boost is more significant for a viscosity contrast (viscosity of cytoplasm over that the suspending fluid) equal to a known value for RBCs, as compared to the case without viscosity contrast. As we increase the adhesion energy (the pathological range), a noteworthy decline in platelet margination is found, albeit that for some flow strength the platelet margination reaches a minimum and increases again at higher adhesion energy. These results can be attributed to a combination of lift generated by the bounding walls and the formation of RBC clusters. Notably, our study sheds light on a critical consequence of excessive adhesion, typically observed in pathological conditions like diabetes mellitus.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"13 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142227810","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 : 2024-08-13DOI: 10.1103/physrevfluids.9.083903
Artur Gesla, Yohann Duguet, Patrick Le Quéré, Laurent Martin Witkowski
Rotor-stator cavity flows are known to exhibit unsteady flow structures in the form of circular and spiral rolls. While the origin of the spirals is well understood, that of the circular rolls is not. In the present study the axisymmetric flow in an aspect ratio cavity is revisited numerically using recent concepts and tools from bifurcation theory. It is confirmed that a linear instability takes place at a finite critical Reynolds number and that there exists a subcritical branch of large amplitude chaotic solutions. This motivates the search for subcritical finite-amplitude solutions. The branch of periodic states born in a Hopf bifurcation at , identified using a self-consistent method (SCM) and arclength continuation, is found to be supercritical. The associated solutions only exist, however, in a very narrow range of and do not explain the subcritical chaotic rolls. Another subcritical branch of periodic solutions is found using the harmonic balance method with an initial guess obtained by SCM. In addition, edge states separating the steady laminar and chaotic regimes are identified using a bisection algorithm. These edge states are biperiodic in time for most values of , where their dynamics is analyzed in detail. Both solution branches fold around at approximately the same value of , which is lower than yet still larger than the values reported in experiments. This suggests that, at least in the absence of external forcing, sustained chaotic rolls have their origin in the bifurcations from these unstable solutions.
众所周知，转子-定子空腔流表现出圆形和螺旋形的不稳定流动结构。虽然螺旋的起源已为人熟知，但圆卷的起源尚不清楚。本研究利用分岔理论的最新概念和工具，对长径比 R/H=10 的空腔中的轴对称流动进行了数值研究。研究证实，在有限临界雷诺数 Re=Rec 时会出现线性不稳定性，并且存在大振幅混沌解的亚临界分支。这激发了对亚临界有限振幅解的探索。利用自洽方法（SCM）和 arclength continuation 确定了在 Re=Rec 处产生于霍普夫分岔的周期状态分支，发现它是超临界的。然而，相关解仅存在于 Re 非常窄的范围内，无法解释亚临界混沌辊。利用谐波平衡法和单片机获得的初始猜测，发现了周期解的另一个亚临界分支。此外，还利用分段算法确定了分隔稳定层流和混沌状态的边缘状态。在大多数 Re 值下，这些边缘状态在时间上是双周期的，对它们的动力学进行了详细分析。两个解分支在近似相同的 Re 值处折叠，该值低于 Rec 值，但仍大于实验报告的值。这表明，至少在没有外部强迫的情况下，持续的混沌滚动起源于这些不稳定解的分岔。
{"title":"Subcritical axisymmetric solutions in rotor-stator flow","authors":"Artur Gesla, Yohann Duguet, Patrick Le Quéré, Laurent Martin Witkowski","doi":"10.1103/physrevfluids.9.083903","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.083903","url":null,"abstract":"Rotor-stator cavity flows are known to exhibit unsteady flow structures in the form of circular and spiral rolls. While the origin of the spirals is well understood, that of the circular rolls is not. In the present study the axisymmetric flow in an aspect ratio <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mi>R</mi><mo>/</mo><mi>H</mi><mo>=</mo><mn>10</mn></mrow></math> cavity is revisited numerically using recent concepts and tools from bifurcation theory. It is confirmed that a linear instability takes place at a finite critical Reynolds number <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> and that there exists a subcritical branch of large amplitude chaotic solutions. This motivates the search for subcritical finite-amplitude solutions. The branch of periodic states born in a Hopf bifurcation at <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>, identified using a self-consistent method (SCM) and arclength continuation, is found to be supercritical. The associated solutions only exist, however, in a very narrow range of <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mtext>Re</mtext></math> and do not explain the subcritical chaotic rolls. Another subcritical branch of periodic solutions is found using the harmonic balance method with an initial guess obtained by SCM. In addition, edge states separating the steady laminar and chaotic regimes are identified using a bisection algorithm. These edge states are biperiodic in time for most values of <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mtext>Re</mtext></math>, where their dynamics is analyzed in detail. Both solution branches fold around at approximately the same value of <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mtext>Re</mtext></math>, which is lower than <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mtext>Re</mtext><mi>c</mi></msub></math> yet still larger than the values reported in experiments. This suggests that, at least in the absence of external forcing, sustained chaotic rolls have their origin in the bifurcations from these unstable solutions.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"2 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142210867","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}
Fast and accurate predictions of turbulent flows are of great importance in the science and engineering field. In this paper, we investigate the implicit U-Net enhanced Fourier neural operator (IUFNO) in the stable prediction of long-time dynamics of three-dimensional (3D) turbulent channel flows. The trained IUFNO models are tested in the large-eddy simulations (LES) at coarse grids for three friction Reynolds numbers: , 395, and 590. The adopted near-wall mesh grids are tangibly coarser than the general requirements for wall-resolved LES. Compared to the original Fourier neural operator (FNO), the implicit FNO (IFNO), and U-Net enhanced FNO (UFNO), the IUFNO model has a much better long-term predictive ability. The numerical experiments show that the IUFNO framework outperforms the traditional dynamic Smagorinsky model and the wall-adapted local eddy-viscosity model in the predictions of a variety of flow statistics and structures, including the mean and fluctuating velocities, the probability density functions (PDFs) and joint PDF of velocity fluctuations, the Reynolds stress profile, the kinetic energy spectrum, and the Q-criterion (vortex structures). Meanwhile, the trained IUFNO models are computationally much faster than the traditional LES models. Thus, the IUFNO model is a promising approach for the fast prediction of wall-bounded turbulent flow.
{"title":"Prediction of turbulent channel flow using Fourier neural operator-based machine-learning strategy","authors":"Yunpeng Wang, Zhijie Li, Zelong Yuan, Wenhui Peng, Tianyuan Liu, Jianchun Wang","doi":"10.1103/physrevfluids.9.084604","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.084604","url":null,"abstract":"Fast and accurate predictions of turbulent flows are of great importance in the science and engineering field. In this paper, we investigate the implicit U-Net enhanced Fourier neural operator (IUFNO) in the stable prediction of long-time dynamics of three-dimensional (3D) turbulent channel flows. The trained IUFNO models are tested in the large-eddy simulations (LES) at coarse grids for three friction Reynolds numbers: <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><msub><mtext>Re</mtext><mi>τ</mi></msub><mo>≈</mo><mn>180</mn></mrow></math>, 395, and 590. The adopted near-wall mesh grids are tangibly coarser than the general requirements for wall-resolved LES. Compared to the original Fourier neural operator (FNO), the implicit FNO (IFNO), and U-Net enhanced FNO (UFNO), the IUFNO model has a much better long-term predictive ability. The numerical experiments show that the IUFNO framework outperforms the traditional dynamic Smagorinsky model and the wall-adapted local eddy-viscosity model in the predictions of a variety of flow statistics and structures, including the mean and fluctuating velocities, the probability density functions (PDFs) and joint PDF of velocity fluctuations, the Reynolds stress profile, the kinetic energy spectrum, and the Q-criterion (vortex structures). Meanwhile, the trained IUFNO models are computationally much faster than the traditional LES models. Thus, the IUFNO model is a promising approach for the fast prediction of wall-bounded turbulent flow.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"24 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-08-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141936230","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 : 2024-08-12DOI: 10.1103/physrevfluids.9.083902
V. Srinivasan, X. Tan, E. Whitely, I. Wright, A. Dhotre, J. Yang
The effect of viscosity contrast between a jet and its surroundings is experimentally investigated using density-matched fluids. A gravity-driven flow is established with a jet of saltwater emerging into an ambient medium composed of high-viscosity propylene glycol. Jet Reynolds numbers, , ranging from 1600 to 3400 were studied for an ambient-to-jet viscosity ratio, , between 1 and 50. Visualization suggests that at low values of the viscosity ratio, the jet breakdown mode is axisymmetric, while helical modes develop at high values of viscosity ratio. The transition between these two modes is attempted to be delineated using a variety of diagnostic tools. Hot-film anemometry measurements indicate that the onset of the helical mode is accompanied by the appearance of a discrete peak in the frequency spectrum of velocity fluctuations, which exhibits little spatial variation for the first several diameters in the downstream direction. Laser-induced fluorescence (LIF) is used to identify the jet boundary against the background. An analysis of high-speed images acquired using the LIF technique enables identification of the spatial growth rate of waves on the jet boundary, as well as the frequency of oscillation of the weakly diffusive interface. Temporal fluctuations of fluorescence intensity are found to be spatially invariant in the jet near field, further attesting to behavior consistent with that of a self-sustained oscillation whose frequency depends on the viscosity ratio. The observed frequencies show trends similar to those of absolutely unstable modes calculated from spatiotemporal linear stability theory presented in a companion paper. Spectral proper orthogonal decomposition was used to analyze the images and identify the various spatial modes, and suggests the existence of a single dominant mode. Together, these observations provide strong circumstantial evidence for the existence of a global mode that arises from the absolute instability of velocity and viscosity profiles in a region close to the nozzle exit plane.
我们使用密度匹配流体对射流及其周围环境之间的粘度对比效应进行了实验研究。在重力驱动下，盐水射流进入由高粘度丙二醇组成的环境介质。研究了环境与射流的粘度比 M 在 1 到 50 之间时，射流的雷诺数 Re 在 1600 到 3400 之间。可视化结果表明，在粘度比值较低时，射流击穿模式为轴对称模式，而在粘度比值较高时，则会出现螺旋模式。我们尝试使用各种诊断工具来划分这两种模式之间的过渡。热膜风速测量法的测量结果表明，螺旋模式的出现伴随着速度波动频谱中出现一个离散的峰值，该峰值在下游方向的前几个直径处几乎没有空间变化。激光诱导荧光（LIF）用于识别背景中的射流边界。通过分析利用激光诱导荧光技术获取的高速图像，可以确定射流边界上波的空间增长率以及弱扩散界面的振荡频率。研究发现，荧光强度的时间波动在射流近场是空间不变的，这进一步证明了其行为与频率取决于粘度比的自持振荡一致。观测到的频率显示出与根据时空线性稳定性理论计算出的绝对不稳定模式相似的趋势，该理论已在另一篇论文中介绍。光谱正交分解用于分析图像和识别各种空间模式，结果表明存在单一主导模式。总之，这些观测结果为全局模式的存在提供了有力的旁证，这种模式是由靠近喷嘴出口平面区域的速度和粘度剖面的绝对不稳定性引起的。
{"title":"Self-sustained oscillations in a low-viscosity round jet","authors":"V. Srinivasan, X. Tan, E. Whitely, I. Wright, A. Dhotre, J. Yang","doi":"10.1103/physrevfluids.9.083902","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.083902","url":null,"abstract":"The effect of viscosity contrast between a jet and its surroundings is experimentally investigated using density-matched fluids. A gravity-driven flow is established with a jet of saltwater emerging into an ambient medium composed of high-viscosity propylene glycol. Jet Reynolds numbers, <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>Re</mi></math>, ranging from 1600 to 3400 were studied for an ambient-to-jet viscosity ratio, <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>M</mi></math>, between 1 and 50. Visualization suggests that at low values of the viscosity ratio, the jet breakdown mode is axisymmetric, while helical modes develop at high values of viscosity ratio. The transition between these two modes is attempted to be delineated using a variety of diagnostic tools. Hot-film anemometry measurements indicate that the onset of the helical mode is accompanied by the appearance of a discrete peak in the frequency spectrum of velocity fluctuations, which exhibits little spatial variation for the first several diameters in the downstream direction. Laser-induced fluorescence (LIF) is used to identify the jet boundary against the background. An analysis of high-speed images acquired using the LIF technique enables identification of the spatial growth rate of waves on the jet boundary, as well as the frequency of oscillation of the weakly diffusive interface. Temporal fluctuations of fluorescence intensity are found to be spatially invariant in the jet near field, further attesting to behavior consistent with that of a self-sustained oscillation whose frequency depends on the viscosity ratio. The observed frequencies show trends similar to those of absolutely unstable modes calculated from spatiotemporal linear stability theory presented in a companion paper. Spectral proper orthogonal decomposition was used to analyze the images and identify the various spatial modes, and suggests the existence of a single dominant mode. Together, these observations provide strong circumstantial evidence for the existence of a global mode that arises from the absolute instability of velocity and viscosity profiles in a region close to the nozzle exit plane.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"46 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-08-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141968973","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 : 2024-08-12DOI: 10.1103/physrevfluids.9.084603
Mitesh Thakor, Yiyang Sun, Datta V. Gaitonde
We investigate the perturbation dynamics in a supersonic shear layer using a combination of large-eddy simulations (LES) and linear-operator-based input-output analysis. The flow consists of two streams—a main stream (Mach 1.23) and a bypass stream (Mach 1.0)—separated by a splitter plate of nonnegligible thickness. We employ spectral proper orthogonal decomposition to identify the most energetic coherent structures and bispectral mode decomposition to explore the nonlinear energy cascade within the turbulent shear-layer flow. Structures at the dominant frequency are also obtained from a resolvent analysis of the mean flow. We observe higher gain at the dominant frequency in resolvent analysis, indicating the dominance of Kelvin-Helmholtz (KH) instability as the primary disturbance energy-amplification mechanism. To focus on realizable actuator placement locations, we further conduct an input-output analysis by restricting a state variable and spatial location of an input and output. Various combinations of inputs and output indicate that the splitter plate trailing surface is the most sensitive location for introducing a perturbation. Upper and lower surface inputs are less influential in modulating wavepackets in the shear layer but introduce pressure instability waves in the main and bypass streams, respectively. The analysis reveals that the phase speed of pressure waves depends on the state variable and input location combination. For all combinations, the KH instability plays a key role in amplification, which reduces significantly as the input location is moved upstream relative to the splitter plate trailing edge. Furthermore, two-dimensional nonlinear simulations with unsteady input at the upper surface of the splitter plate show remarkable similarities between pressure modes obtained through dynamic mode decomposition and those predicted from linear input-output analysis at a given frequency. This study emphasizes the strength of linear analysis and demonstrates that predicted coherent structures remain active in highly nonlinear turbulent flow. The insights gained from the input-output analysis can be further leveraged to formulate practical flow control strategies.
{"title":"Responses to disturbance of supersonic shear layer: Input-output analysis","authors":"Mitesh Thakor, Yiyang Sun, Datta V. Gaitonde","doi":"10.1103/physrevfluids.9.084603","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.084603","url":null,"abstract":"We investigate the perturbation dynamics in a supersonic shear layer using a combination of large-eddy simulations (LES) and linear-operator-based input-output analysis. The flow consists of two streams—a main stream (Mach 1.23) and a bypass stream (Mach 1.0)—separated by a splitter plate of nonnegligible thickness. We employ spectral proper orthogonal decomposition to identify the most energetic coherent structures and bispectral mode decomposition to explore the nonlinear energy cascade within the turbulent shear-layer flow. Structures at the dominant frequency are also obtained from a resolvent analysis of the mean flow. We observe higher gain at the dominant frequency in resolvent analysis, indicating the dominance of Kelvin-Helmholtz (KH) instability as the primary disturbance energy-amplification mechanism. To focus on realizable actuator placement locations, we further conduct an input-output analysis by restricting a state variable and spatial location of an input and output. Various combinations of inputs and output indicate that the splitter plate trailing surface is the most sensitive location for introducing a perturbation. Upper and lower surface inputs are less influential in modulating wavepackets in the shear layer but introduce pressure instability waves in the main and bypass streams, respectively. The analysis reveals that the phase speed of pressure waves depends on the state variable and input location combination. For all combinations, the KH instability plays a key role in amplification, which reduces significantly as the input location is moved upstream relative to the splitter plate trailing edge. Furthermore, two-dimensional nonlinear simulations with unsteady input at the upper surface of the splitter plate show remarkable similarities between pressure modes obtained through dynamic mode decomposition and those predicted from linear input-output analysis at a given frequency. This study emphasizes the strength of linear analysis and demonstrates that predicted coherent structures remain active in highly nonlinear turbulent flow. The insights gained from the input-output analysis can be further leveraged to formulate practical flow control strategies.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"57 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-08-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141936215","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 : 2024-08-12DOI: 10.1103/physrevfluids.9.084605
Mostafa Kamal, Perry L. Johnson
In Navier-Stokes turbulence, a bottleneck effect in the energy cascade near the viscous cutoff causes an overshoot in the energy spectrum, or spectral bump, relative to Komogorov's −5/3 power-law scaling. A similar spectral overshoot occurs in large-eddy simulations (LES) when an eddy viscosity model is used. It is not a viscous phenomenon, but rather is caused by error in the residual stress model. This artificial bottleneck effect in LES leads to an over-prediction of kinetic energy even if a reliable dynamic procedure is used to accurately capture the spectral decay at the cutoff length scale. Recently, Johnson [J. Fluid Mech.934, A30 (2022)] introduced a physics-inspired generalization of the concept of spatial filtering that provides a dynamic procedure that does not require a test filter calculation. In this paper, this method of Stokes flow regularization (SFR) is used alongside fundamental considerations related to kinetic energy to generate a range of LES models to explore the artificial bottleneck effect in more detail. The coefficients for each dynamic model are determined locally, without the need of averaging over homogeneous directions. The theory directly provides stabilizing elements such as local averaging of coefficients. A posteriori tests of the models in isotropic turbulence are reported, demonstrating the robustness of the SFR-based dynamic procedure for a range of model forms and providing a framework for fair comparisons between them in terms of their impact on the bottleneck effect. An effective means of mitigating the bottleneck effect is to introduce a nonlinear gradient component in the residual stress closure, forming a dynamic mixed model. One primary reason for the efficacy of this approach is that the nonlinear gradient model is able to accurately capture aspects of the local structure of the residual stresses, leading to a better representation of energy cascade efficiencies.
{"title":"Artificial bottleneck effect in large eddy simulations","authors":"Mostafa Kamal, Perry L. Johnson","doi":"10.1103/physrevfluids.9.084605","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.084605","url":null,"abstract":"In Navier-Stokes turbulence, a bottleneck effect in the energy cascade near the viscous cutoff causes an overshoot in the energy spectrum, or spectral bump, relative to Komogorov's −5/3 power-law scaling. A similar spectral overshoot occurs in large-eddy simulations (LES) when an eddy viscosity model is used. It is not a viscous phenomenon, but rather is caused by error in the residual stress model. This artificial bottleneck effect in LES leads to an over-prediction of kinetic energy even if a reliable dynamic procedure is used to accurately capture the spectral decay at the cutoff length scale. Recently, Johnson [<span>J. Fluid Mech.</span> <b>934</b>, A30 (2022)] introduced a physics-inspired generalization of the concept of spatial filtering that provides a dynamic procedure that does not require a test filter calculation. In this paper, this method of Stokes flow regularization (SFR) is used alongside fundamental considerations related to kinetic energy to generate a range of LES models to explore the artificial bottleneck effect in more detail. The coefficients for each dynamic model are determined locally, without the need of averaging over homogeneous directions. The theory directly provides stabilizing elements such as local averaging of coefficients. <i>A posteriori</i> tests of the models in isotropic turbulence are reported, demonstrating the robustness of the SFR-based dynamic procedure for a range of model forms and providing a framework for fair comparisons between them in terms of their impact on the bottleneck effect. An effective means of mitigating the bottleneck effect is to introduce a nonlinear gradient component in the residual stress closure, forming a dynamic mixed model. One primary reason for the efficacy of this approach is that the nonlinear gradient model is able to accurately capture aspects of the local structure of the residual stresses, leading to a better representation of energy cascade efficiencies.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"77 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-08-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141936231","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":"14 1","pages":""},"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":"89 1","pages":""},"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":"44 1","pages":""},"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":"43 1","pages":""},"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}
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