arXiv: Fluid Dynamics最新文献_第2页

Characteristic Sensitivity of Turbulent Flow within a Porous Medium under Initial Conditions 初始条件下多孔介质湍流特性敏感性研究

arXiv: Fluid Dynamics Pub Date : 2020-12-07 DOI: 10.7566/jpsj.90.024401

Takehito Suzuki

{"title":"Characteristic Sensitivity of Turbulent Flow within a Porous Medium under Initial Conditions","authors":"Takehito Suzuki","doi":"10.7566/jpsj.90.024401","DOIUrl":"https://doi.org/10.7566/jpsj.90.024401","url":null,"abstract":"Flows within porous media play important roles in many scientific and industrial systems. However, the case wherein such flows become turbulent has not been completely understood, particularly, from a mathematical viewpoint. In this study, the $k-varepsilon$ model (the variable $k$ denotes the turbulent kinetic energy per unit mass and $varepsilon$ the dissipation rate for the turbulent kinetic energy), which has been widely used for the usual turbulent flow in a clear fluid, was applied to a turbulent flow through porous media. If a homogeneous, averaged flow and homogeneous isotropic turbulence are assumed, the governing equations for the variables $k$ and $varepsilon$ describe a straight line as a nullcline common to both the variables. The nullcline was shown to be a line attractor. A temporal evolution of the eddy viscosity was also obtained, and the initial and final values of the eddy viscosity were observed to be related to a power law, indicating universal sensitivity. This sensitivity originates from the common nullcline and is not observed for the usual turbulent flow. Finally, nonlinear mathematical and seismological implications were provided using based on the results obtained.","PeriodicalId":328276,"journal":{"name":"arXiv: Fluid Dynamics","volume":"57 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-12-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125745615","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Transition from steady to oscillating convection rolls in Rayleigh-Bénard convection under the influence of a horizontal magnetic field 在水平磁场的影响下，瑞利-巴姆纳德对流从稳定到振荡的对流滚转

arXiv: Fluid Dynamics Pub Date : 2020-12-04 DOI: 10.1103/PHYSREVFLUIDS.6.023502

J. C. Yang, T. Vogt, S. Eckert

{"title":"Transition from steady to oscillating convection rolls in Rayleigh-Bénard convection under the influence of a horizontal magnetic field","authors":"J. C. Yang, T. Vogt, S. Eckert","doi":"10.1103/PHYSREVFLUIDS.6.023502","DOIUrl":"https://doi.org/10.1103/PHYSREVFLUIDS.6.023502","url":null,"abstract":"In this study we consider the effect of a horizontal magnetic field on the Rayleigh-B'enard convection in a finite liquid metal layer contained in a cuboid vessel (200 times 200 times 40 mm^3). Laboratory experiments are performed for measuring temperature and flow field in the alloy GaInSn at Prandtl number Pr = 0.03 and in a Rayleigh number range 2.3 times 10^4 < Ra < 2.6 times 10^5. The field strength is varied up to a maximum value of 320 mT (Ha = 2470, Q = 6.11 times 10^6). The magnetic field forces the flow to form two-dimensional rolls parallel to the direction of the field lines. The experiments confirm the predictions made by Busse and Clever (J. M'ecanique Th'eorique et Appliqu'ee, 1983) who showed that the application of the horizontal magnetic field extends the range in which steady two-dimensional roll structures exist (Busse balloon) towards higher Ra numbers. A transition from the steady to a time-dependent oscillatory flow occurs when Ra exceeds a critical value for a given Chandrasekhar number Q, which is also equivalent to a reduction of the ratio Q/Ra. Our measurements reveal that the first developing oscillations are clearly of two-dimensional nature, in particular a mutual increase and decrease in the size of adjacent convection rolls is observed without the formation of any detectable gradients in the velocity field along the magnetic field direction. At a ratio of Q/Ra = 1, the first 3D structures appear, which initially manifest themselves in a slight inclination of the rolls with respect to the magnetic field direction. Immediately in the course of this, there arise also disturbances in the spaces between adjacent convection rolls, which are advected along the rolls due to the secondary flow driven by Ekman pumping. The transition to fully-developed three-dimensional structures and then to a turbulent regime takes place with further lowering Q/Ra.","PeriodicalId":328276,"journal":{"name":"arXiv: Fluid Dynamics","volume":"12 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-12-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121787921","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 13

Synchronizing subgrid scale models of turbulence to data 将湍流的子网格尺度模型与数据同步

arXiv: Fluid Dynamics Pub Date : 2020-12-01 DOI: 10.1063/5.0031835

M. Buzzicotti, P. Clark Di Leoni

引用次数: 20

Analytical solution for an acoustic boundary layer around an oscillating rigid sphere 振动刚性球周围声边界层的解析解

arXiv: Fluid Dynamics Pub Date : 2020-11-25 DOI: 10.1063/5.0033933

E. Klaseboer, Qiang Sun, D. Chan

{"title":"Analytical solution for an acoustic boundary layer around an oscillating rigid sphere","authors":"E. Klaseboer, Qiang Sun, D. Chan","doi":"10.1063/5.0033933","DOIUrl":"https://doi.org/10.1063/5.0033933","url":null,"abstract":"Analytical solutions in fluid dynamics can be used to elucidate the physics of complex flows and to serve as test cases for numerical models. In this work, we present the analytical solution for the acoustic boundary layer that develops around a rigid sphere executing small amplitude harmonic rectilinear motion in a compressible fluid. The mathematical framework that describes the primary flow is identical to that of wave propagation in linearly elastic solids, the difference being the appearance of complex instead of real valued wave numbers. The solution reverts to well-known classical solutions in special limits: the potential flow solution in the thin boundary layer limit, the oscillatory flat plate solution in the limit of large sphere radius and the Stokes flow solutions in the incompressible limit of infinite sound speed. As a companion analytical result, the steady second order acoustic streaming flow is obtained. This streaming flow is driven by the Reynolds stress tensor that arises from the axisymmetric first order primary flow around such a rigid sphere. These results are obtained with a linearization of the non-linear Navier-Stokes equations valid for small amplitude oscillations of the sphere. The streaming flow obeys a time-averaged Stokes equation with a body force given by the Nyborg model in which the above mentioned primary flow in a compressible Newtonian fluid is used to estimate the time-averaged body force. Numerical results are presented to explore different regimes of the complex transverse and longitudinal wave numbers that characterize the primary flow.","PeriodicalId":328276,"journal":{"name":"arXiv: Fluid Dynamics","volume":"117 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-11-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124654545","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 5

Multiscale energy budget of inertially driven turbulence in normal and superfluid helium 正常和超流氦中惯性驱动湍流的多尺度能量收支

arXiv: Fluid Dynamics Pub Date : 2020-11-24 DOI: 10.1103/PhysRevFluids.6.064604

F. Sy, P. Diribarne, B. Rousset, M. Gibert, M. Bourgoin

{"title":"Multiscale energy budget of inertially driven turbulence in normal and superfluid helium","authors":"F. Sy, P. Diribarne, B. Rousset, M. Gibert, M. Bourgoin","doi":"10.1103/PhysRevFluids.6.064604","DOIUrl":"https://doi.org/10.1103/PhysRevFluids.6.064604","url":null,"abstract":"In this paper we present a novel hydrodynamic experiment using liquid $^4$He. The flow is forced inertially by a canonical oscillating grid using either its normal (He~I) or superfluid (He~II) phase, generating a statistically stationary turbulence. We characterise the turbulent properties of the flow using 2D Lagrangian Particle tracking on hollow glass micro-spheres. As expected for tracer particles, the Voronoi tessellation on particle positions does not show a significant departure from a random Poisson process neither in He~I nor He~II phase. Particles' positions are tracked with high temporal resolution, allowing to resolve velocity fluctuations at integral and inertial scales while properly assessing the noise contribution. Additionally, we differentiate the particles' positions (by convolution with Gaussian kernels) in order to access small scale quantities like acceleration. Using these measured quantities and the formalism of classical Homogeneous Isotropic Turbulence (HIT) to perform an energy budget across scales we extract the energy injection rate at the large scale, the energy flux cascading through inertial scales, down to small scales at which it is dissipated. We found that in such inertially driven turbulence, regardless of the normal or superfluid state of the fluid, estimates of energy at the different scales are compatible with each other and consistent with oscillating grid turbulence results reported for normal fluids in the literature. The largest discrepancy shows up at small scales where the signal to noise ratio is harder to control and where the 2D measurement is contaminated by the 3D nature of the flow. This motivates to focus future experimental projects towards small scales, low noise and 3D measurements.","PeriodicalId":328276,"journal":{"name":"arXiv: Fluid Dynamics","volume":"148 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-11-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122555242","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 3

Phase-locking of laminar wake to periodic vibrations of a circular cylinder 圆柱周期性振动对层流尾流锁相的影响

arXiv: Fluid Dynamics Pub Date : 2020-11-19 DOI: 10.1103/PHYSREVFLUIDS.6.034401

M. A. Khodkar, J. Klamo, K. Taira

{"title":"Phase-locking of laminar wake to periodic vibrations of a circular cylinder","authors":"M. A. Khodkar, J. Klamo, K. Taira","doi":"10.1103/PHYSREVFLUIDS.6.034401","DOIUrl":"https://doi.org/10.1103/PHYSREVFLUIDS.6.034401","url":null,"abstract":"Phase synchronization between the vortex shedding behind a two-dimensional circular cylinder and its vibrations is investigated using the phase-reduction analysis. Leveraging this approach enables the development of a one-dimensional, linear model with respect to the limit-cycle attractor of the laminar wake, which accurately describes the phase dynamics of the high-dimensional, nonlinear fluid flow and its response to rotational, transverse and longitudinal vibrations of the cylinder. This phase-based model is derived by assessing the phase-response and sensitivity of the wake dynamics to impulse perturbations of the cylinder, which can be performed in simulations and experiments. The resulting model in turn yields the theoretical conditions required for phase-locking between the cylinder vibrations and the wake. We furthermore show that this synchronization mechanism can be employed to stabilize the wake and subsequently reduce drag. We also uncover the circumstances under which the concurrent occurrence of different vibrational motions can be used to promote or impede synchronization. These findings provide valuable insights for the study of vortex-induced body oscillations, the enhancement of aerodynamic performance of flyers, or the mitigation of structural vibrations by synchronizing or desynchronizing the oscillatory motions of body to the periodic wake.","PeriodicalId":328276,"journal":{"name":"arXiv: Fluid Dynamics","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-11-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122045629","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 6

Spinning and tumbling of long fibers in isotropic turbulence 长纤维在各向同性湍流中的纺丝和翻滚

arXiv: Fluid Dynamics Pub Date : 2020-11-17 DOI: 10.1103/PHYSREVFLUIDS.6.044610

T. Oehmke, A. Bordoloi, E. Variano, G. Verhille

引用次数: 8

Theoretical model for the separated flow around an accelerating flat plate using time-dependent self-similarity 基于时间相关自相似性的加速平板分离流理论模型

arXiv: Fluid Dynamics Pub Date : 2020-11-17 DOI: 10.1103/PhysRevFluids.6.054701

A. DeVoria, K. Mohseni

{"title":"Theoretical model for the separated flow around an accelerating flat plate using time-dependent self-similarity","authors":"A. DeVoria, K. Mohseni","doi":"10.1103/PhysRevFluids.6.054701","DOIUrl":"https://doi.org/10.1103/PhysRevFluids.6.054701","url":null,"abstract":"We present a model appropriate to the initial motion (2-3 chords of travel) of a flat-plate airfoil accelerating in an inviscid fluid. The separated flow structures are represented as vortex sheets in the conventional manner and similarity expansions locally applicable to the leading and trailing edges of the plate are developed. The topological character of vortex sheets is maintained rather than resorting to point vortex discretizations. Beyond this, there are two theoretical novelties to our approach as compared to previous studies. First, an expansion is applied to the attached outer flow rather than the vortex sheet circulations and positions. This allows the asymmetric effect of the sweeping component of the free-stream flow parallel to the plate to be built-in to the same governing equation as the singular-order flow. Second, we develop a time-dependent self similarity procedure that allows the modeling of more complex evolution of the flow structures. This is accomplished through an implicit time variation of the similarity variables. As a collective result, the predicted vortex dynamics and forces on the plate compare favorably to Navier-Stokes simulations. Lastly, the model is utilized to provide some new intuition about the separated flow at the leading edge.","PeriodicalId":328276,"journal":{"name":"arXiv: Fluid Dynamics","volume":"49 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-11-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131883231","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 1

Traveling waves are hydrodynamically optimal for long-wavelength flagella 行波对长波长鞭毛是流体动力学最优的

arXiv: Fluid Dynamics Pub Date : 2020-11-17 DOI: 10.1103/physrevfluids.5.123101

E. Lauga

引用次数: 2

Direct versus indirect hydrodynamic interactions during bundle formation of bacterial flagella 细菌鞭毛束形成过程中的直接与间接流体动力学相互作用

arXiv: Fluid Dynamics Pub Date : 2020-11-17 DOI: 10.1103/physrevfluids.5.123102

Alexander Chamolly, E. Lauga

{"title":"Direct versus indirect hydrodynamic interactions during bundle formation of bacterial flagella","authors":"Alexander Chamolly, E. Lauga","doi":"10.1103/physrevfluids.5.123102","DOIUrl":"https://doi.org/10.1103/physrevfluids.5.123102","url":null,"abstract":"Most motile bacteria swim in viscous fluids by rotating multiple helical flagellar filaments. These semi-rigid filaments repeatedly join ('bundle') and separate ('unbundle'), resulting in a two-gait random walk-like motion of the cell. In this process, hydrodynamic interactions between the filaments are known to play an important role and can be categorised into two distinct types: direct interactions mediated through flows that are generated through the actuation of the filaments themselves, and indirect interactions mediated through the motion of the cell body (i.e. flows induced in the swimming frame that result from propulsion). To understand the relative importance of these two types of interactions, we study a minimal singularity model of flagellar bundling. Using hydrodynamic images, we solve for the flow analytically and compute both direct and indirect interactions exactly as a function of the length of the flagellar filaments and their angular separation. We show (i) that the generation of thrust by flagella alone is sufficient to drive the system towards a bundled state through both types of interaction; (ii) that indirect advection dominates for long filaments and at wide separation, i.e. primarily during the early stages of the bundling process; and (iii) that, in contrast, direct interactions dominate when flagellar filaments are in each other's wake, which we characterise mathematically. We further introduce a numerical elastohydrodynamic model that allows us to compute the dynamics of the helical axes of each flagellar filament while analysing direct and indirect interactions separately. With this we show (iv) that the shift in balance between direct and indirect interactions is non-monotonic during the bundling process, with a peak in direct dominance, and that different sections of the flagella are affected by these changes to different extents.","PeriodicalId":328276,"journal":{"name":"arXiv: Fluid Dynamics","volume":"118 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2020-11-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133457738","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 5