Physical Review Fluids最新文献

{"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}

{"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}

{"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}

{"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}

{"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}

{"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}

{"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>&lt;</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}

{"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}

{"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}

{"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}