Physical Review Fluids最新文献

{"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}

{"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":"37 3 1","pages":""},"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}

{"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":"22 1","pages":""},"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}

{"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":"30 1","pages":""},"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}

{"title":"Improved two-temperature model with correction of non-Boltzmann effect for oxygen and nitrogen","authors":"Rui Xiong, Yufeng Han, Wei Cao","doi":"10.1103/physrevfluids.9.083201","DOIUrl":"https://doi.org/10.1103/physrevfluids.9.083201","url":null,"abstract":"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 <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi mathvariant=\"normal\">N</mi><mn>2</mn></msub></math> and <math xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi mathvariant=\"normal\">O</mi><mn>2</mn></msub></math>. 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.","PeriodicalId":20160,"journal":{"name":"Physical Review Fluids","volume":"3 1","pages":""},"PeriodicalIF":2.7,"publicationDate":"2024-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141936220","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}