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TRPIV investigation of space-time correlation in turbulent flows over flat and wavy walls

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Acta Mechanica Sinica 2014年第4期30卷 468-479页

作者： Wei Wang Xin-Lei Guan Nan Jiang Department of Mechanics Tianjin University Tianjin Key Laboratory of Modern Engineering Mechanics The State Key Laboratory of Nonlinear Mechanics Institute of Mechanics Chinese Academy of Sciences

The present experimental work is devoted to in- vestigate a new space-time correlation model for the turbulent boundary layer over a flat and a wavy walls. A turbulent boundary layer flow at Reo = 2460 is measured by tomographic time-resolved particle image velocimetry （Tomo-TRPIV）. The space-time correlations of instantaneous streamwise fluctuation velocity are calculated at 3 different wall-normal locations in logarithmic layer. It is found that the scales of coherent structure increase with moving far away from the wall. The growth of scales is a manifestation of the growth of prevalent coherent structures in the turbulent boundary layer like hairpin vortex or hairpin packets when they lift up. The resulting contours of the space-time correlation exhibit elliptic-like shapes rather than straight lines. It is suggested that, instead of Taylor hypothesis, the elliptic model of the space-time correlation is valid for the wallbounded turbulent flow over either a flat wall or a wavy wall. The elliptic iso-correlation curves have a uniform preferred orientation whose slope is determined by the convection velocity. The convection velocity derived from the space-time correlation represents the velocity at which the large-scale eddies carry small-scale eddies. The sweep velocity rep- resents the distortions of the small-scale eddies and is intimately associated with the fluctuation velocity in the logarithmic layer of turbulent boundary layers. The nondimensionalized correlation curves confirm that the elliptic model is more proper for approximating the space-time correlation than Taylor hypothesis, because the latter can not embody the small-scale motions which have non-negligible distortions. A second flow over a wavy wall is also recorded using TRPIV. Due to the combined effect of shear layers and the adverse pressure gradient, the space-time correlation does not show an elliptic-like shape at some specific heights over the wavy wall, but in the outer region of the wav

关键词： Tomographic particle image velocimetry Tur-bulent boundary layer Wavy wall space-time correlation Taylor hypothesis Elliptic model

space-time correlations of passive scalar in Kraichnan model

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Theoretical & Applied Mechanics Letters 2023年第5期13卷 338-340页

作者： Ping-Fan Yang Liubin Pan Guowei He State Key Laboratory of Nonlinear Mechanics Institute of MechanicsChinese Academy of SciencesBeijing 100190China School of Engineering Sciences University of Chinese Academy of SciencesBeijing 100049China School of Physics and Astronomy Sun Yat-Sen UniversityZhuhai 519082China

We consider the two-point,two-time(space-time)correlation of passive scalar R(r,τ)in the Kraichnan model under the assumption of homogeneity and *** the fine-gird PDF method,we find that R(r,τ)satisfies a diffusion equation with constant diffusion coefficient determined by velocity variance and molecular *** can be expressed in terms of the two-point,one time correlation of passive scalar,i.e.,R(r,0).Moreover,the decorrelation o R(k,τ),which is the Fourier transform of R(r,τ),is determined byR(k,0)and a diffusion kernal.

关键词： space-time correlation Passive scalar Kraichnan model

space–time correlations in turbulent flow: A review

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Theoretical & Applied Mechanics Letters 2014年第2期4卷 1-16页

作者： James M.Wallace Burgers Program for Fluid Dynamics and Department of Mechanical Engineering University of MarylandCollege Park

This paper reviews some of the principal uses, over almost seven decades, of correlations, in both Eulerian and Lagrangian frames of reference, of properties of turbulent flows at variable spatial locations and variable time in- stants. Commonly called space-time correlations, they have been fundamental to theories and models of turbulence as well as for the analyses of experimental and direct numerical simulation turbulence data.

关键词： turbulence space-time correlation Lagrangian and Eulerian correlations directinteraction approximation Taylor's hypothesis elliptic approximation particle dispersion

Convection and correlation of coherent structure in turbulent boundary layer using tomographic particle image velocimetry

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Chinese Physics B 2014年第10期23卷 323-333页

作者：王维管新蕾姜楠 Department of Mechanics Tianjin University Tianjin Key Laboratory of Modern Engineering Mechanics The State Key Laboratory of Nonlinear Mechanics Institute of Mechanics Chinese Academy of Sciences

The present experimental work focuses on a new model for space-time correlation and the scale-dependencies of convection velocity and sweep velocity in turbulent boundary layer over a flat wail. A turbulent boundary layer flow at Reo = 2460 is measured by tomographic particle image velocimetry （tomographic PIV）. It is demonstrated that arch, cane, and hairpin vortices are dominant in the logarithmic layer. Hairpins and hairpin packets are responsible for the elongated low-momentum zones observed in the instantaneous flow field. The conditionally-averaged coherent structures systemically illustrate the key roles of hairpin vortice in the turbulence dynamic events, such as ejection and sweep events and energy transport. The space-time correlations of instantaneous streamwise fluctuation velocity are calculated and confirm the new elliptic model for the space-time correlation instead of Taylor hypothesis. The convection velocities derived from the space-time correlation and conditionally-averaged method both suggest the scaling with the local mean velocity in the logarithmic layer. Convection velocity result based on Fourier decomposition （FD） shows stronger scale- dependency in the spanwise direction than in streamwise direction. Compared with FD, the proper orthogonal decomposition （POD） has a distinct distribution of convection velocity for the large- and small-scales which are separated in light of their contributions of turbulent kinetic energy.

关键词： turbulent boundary layer tomographic particle image velocimetry space-time correlation ellipticmodel

Scaling of energy spectra in weakly compressible turbulence

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Acta Mechanica Sinica 2017年第3期33卷 500-507页

作者： Yufeng Dong Guowei He The State Key Laboratory of Nonlinear Mechanics Institute of Mechanics Chinese Academy of Sciences School of Engineering Sciences University of Chinese Academy of Sciences

We find an asymptotic expression for the characteristic timescales of decorrelation processes in weakly compressible and isothermal turbulence. This result is used in the Eddy-Damped Quasi-Normal Markovian equation to derive the scalings of compressible energy spectra: (1) if the acoustic waves are dominant, the compressible energy spectra exhibit \(-7/3\) scaling; (2) if local eddy straining is dominant, the compressible energy spectra are scaled as \(-3\). Meanwhile, the energy spectra of incompressible components display the same scaling of \(-5/3\) as those in incompressible turbulence. The direct numerical simulations of weakly compressible turbulence are used to examine the scaling.

关键词： Compressible turbulence Energy spectra Two-point closure space-time correlation

A numerical study of a turbulent mixing layer and its generated noise

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Science China(Physics,Mechanics & Astronomy) 2013年第6期56卷 1157-1164页

作者： LI Dong GUO Li ZHANG Xing HE GuoWei The State Key Laboratory of Nonlinear Mechanics Institute of MechanicsChinese Academy of Sciences

A direct numerical simulation of a turbulent mixing layer with the Reynolds number 500 and the convective Mach number 0.6 is performed and the results obtained are used to study the turbulent flow field and its generated *** the present simulation,the numerical techniques of absorbing buffer zones,artificial convection velocity and spatial filtering are used to achieve nonreflecting boundary *** self-similarity is used to validate the present numerical *** large-scale coherent structures are plotted together with the acoustic waves,which demonstrates the directivity of acoustic *** Lighthill's source and space-time correlations are further *** main contributions to mixing noise are identified in terms of large-scale coherent structures,Lighthill's source and space-time correlations.

关键词： direct numerical simulation mixing layer space-time correlation noise