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Coherent structures in wall turbulence and mechanism for drag reduction control

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Science China(Physics,Mechanics & Astronomy) 2013年第6期56卷 1053-1061页

作者： XU ChunXiao DENG BingQing HUANG WeiXi CUI GuiXiang Department of Engineering Mechanics Tsinghua University

Herein is introduced the mechanism for active control influencing the generation of the near-wall streamwise vortices,which are closely related to the production of high skin friction in wall-bounded turbulent flows.A new opposition control scheme with adjusting control amplitude is proposed and evaluated in turbulent channel flow by direct numerical *** maximum drag reduction rate can be greatly enhanced by the strengthened *** the effectiveness of the control to the coherent structures at high Reynolds numbers is investigated by using a linear transient growth model.

关键词： wall turbulence coherent structure drag reduction active control

Zonal Embedded Grids for LES of Self-Sustaining Structures of wall turbulence

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Tsinghua Science and Technology 2010年第5期15卷 555-560页

作者：李玲苑明顺李全明 State Key Laboratory of Hydroscience and Engineering Tsinghua University China Academy of Safety Science and Technology

In this study,a zonal grid refinement method based on the solution of weakly compressible flow equations with large eddy simulation in the finite volume method（FVM） and dynamic subgrid-scale model framework was used to simulate the turbulence structures of a plane-wall flow with Reynolds number Re=U0δ /ν =10 *** and analysis were conducted on the distributions of time-averaged velocity and velocity fluctuations,as well as on the actual near-wall structures,to verify the accuracy of the turbulence features that were simulated using the zonal grid refinement *** results show that the zonal embedded grid is a very efficient way to illustrate the turbulence structures of the near-wall *** present method is easy to implement and extend to small Mach number flow modeling on a collocated irregular FVM mesh system.

关键词： wall turbulence zonal grid refinement large eddy simulation weakly compressible flow finite volume method

Effect of active control on optimal structures in wall turbulence

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Science China(Physics,Mechanics & Astronomy) 2013年第2期56卷 290-297页

作者： DENG BingQing XU ChunXiao HUANG WeiXi CUI GuiXiang AML Department of Engineering MechanicsTsinghua University

The effect of active control imposed at the wall on optimal structures in wall turbulence is studied by using a linear transient growth *** the detection plane of the control is located in the buffer layer,the influence of the control on the transient growth of large scale motion becomes negligible as Reynolds number ***,if the control signal is detected at the plane located in the logarithm region,the transient growth at large scale can be greatly *** peak values of transient growth resulting from the strong blowing and suction on the wall *** study indicates that a proper selection of control imposed on the wall can suppress the large scale motion in the logarithmic region.

关键词： active control optimal structure wall turbulence

Wavelet spectrum analysis on energy transfer of multi-scale structures in wall turbulence

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Applied Mathematics and Mechanics(English Edition) 2009年第4期30卷 435-443页

作者：夏振炎田砚姜楠 Tianjin Key Laboratory of Modern Engineering Mechanics Department of MechanicsSchool of Mechanical Engineering Tianjin University

The streamwise velocity components at different vertical heights in wall turbulence were measured. Wavelet transform was used to study the turbulent energy spectra, indicating that the global spectrum results from the weighted average of Fourier spectrum based on wavelet scales. W＇avelet transform with more vanishing moments can express the declining of turbulent spectrum. The local wavelet spectrum shows that the physical phenomena such as deformation position in the boundary layer, and the or breakup of eddies are related to the vertical energy-containing eddies exist in a multi-scale form. Moreover, the size of these eddies increases with the measured points moving out of the wall. In the buffer region, the small scale energy-containing eddies with higher frequency are excited. In the outer region, the maximal energy is concentrated in the low-frequency large-scale eddies, and the frequency domain of energy-containing eddies becomes narrower.

关键词： wall turbulence wavelet spectrum turbulent kinetic energy energy-containing eddies burst

EXPERIMENTAL STUDY OF MEASUREMENT FOR DISSIPATION RATE SCALING EXPONENT IN HEATED wall turbulence

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Applied Mathematics and Mechanics(English Edition) 2002年第9期23卷 1035-1044页

作者：姜楠王玉春舒玮王振东 Department of Mechanics Tianjin UniversityTianjin 300072P R China

Experimental investigations have been devoted to the study of scaling law of coarse-grained dissipation rate structure function for velocity and temperature fluctuation of non-isotropic and inhomogeneous turbulent flows at moderate Reynolds number. Much attention has been paid to the case of turbulent boundary layer, which is typically the non-istropic and inhomogeneous trubulence because of the dynamically important existence of organized coherent structure burst process in the near wall region . Longitudinal velocity and temperature have been measured at different vertical positions in turbulent boundary layer over a heated and unheated flat plate in a wind tunnel using hot wire anemometer. The influence of non-isotropy and inhomogeneity and heating the wall on the scaling law of the dissipation rate structure function is studied because of the existence of organized coherent structure burst process in the near wall region . The scaling law of coarse-grained dissipation rate structure function is foun

关键词： heating wall turbulence dissipation rate scaling law hierarchical structure model

New perspective in statistical modeling of wall-bounded turbulence

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Acta Mechanica Sinica 2010年第6期26卷 847-861页

作者： Zhen-Su She Xi Chen You Wu Fazle Hussain State Key Laboratory for turbulence and Complex Systems and Department of Mechanical and Aerospace Engineering College of EngineeringPeking University100871 BeijingChina Department of Mechanical Engineering University of Houston HoustonTX 77204-4792USA

Despite dedicated effort for many decades,statistical description of highly technologically important wall turbulence remains a great *** models are unfortunately incomplete,or empirical,or *** a review of the existing theories of wall turbulence,we present a new framework,called the structure ensemble dynamics （SED）,which aims at integrating the turbulence dynamics into a quantitative description of the mean *** SED theory naturally evolves from a statistical physics understanding of non-equilibrium open systems,such as fluid turbulence, for which mean quantities are intimately coupled with the fluctuation *** from the ensemble-averaged Navier-Stokes（EANS） equations,the theory postulates the existence of a finite number of statistical states yielding a multi-layer picture for wall ***,it uses order functions（ratios of terms in the mean momentum as well as energy equations） to characterize the states and transitions between *** of the SED analysis to an incompressible channel flow and a compressible turbulent boundary layer shows that the order functions successfully reveal the multi-layer structure for wall-bounded turbulence, which arises as a quantitative extension of the traditional view in terms of sub-layer,buffer layer,log layer and wake. Furthermore,an idea of using a set of hyperbolic functions for modeling transitions between layers is proposed for a quantitative model of order functions across the entire flow *** conclude that the SED provides a theoretical framework for expressing the yet-unknown effects of fluctuation structures on the mean quantities,and offers new methods to analyze experimental and simulation *** with asymptotic analysis,it also offers a way to evaluate convergence of *** SED approach successfully describes the dynamics at both momentum and energy levels, in contrast with all prevalent approaches describing the mean velocity profile

关键词： wall turbulence Statistical modeling Structure ensemble dynamics Order function Multi-layer

Study on local topology model of low/high streak structures in wall-bounded turbulence by tomographic time-resolved particle image velocimetry

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Applied Mathematics and Mechanics(English Edition) 2015年第9期36卷 1121-1130页

作者： Haiping TIAN Nan JIANG Yongxiang HUANG Shaoqiong YANG Department of Mechanics Tianjin University Shanghai Institute of Applied Mathematics and Mechanics Shanghai University

The relationship between the in the logarithmic law （log-law） region of bursting event and the low/high-speed streak a turbulent boundary layer is investigated. A tomographic time-resolved particle image velocimetry （TRPIV） system is used to measure the instantaneous three-dimensional-three-component （3D-3C） velocity field. The momentum thickness based Reynolds number is about 2 460. The topological information in the log-law region is obtained experimentally. It is found that the existence of the quadrupole topological structure implies a three-pair hairpin-like vortex packet, which is in connection with the low/high-speed streak. An idealized 3D topological model is then proposed to characterize the observed hairpin vortex packet and low/high-speed streak.

关键词： wall turbulence quadrupole topological structure hairpin vortex low/highspeed streak tomographic time-resolved particle image velocimetry (TRPIV) system

Alignment of inertialess spheroidal particles in flow-structure-dominated regions of turbulent channel flow:shape effect

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Acta Mechanica Sinica 2024年第8期40卷 45-66页

作者： Zhiwen Cui Lihao Zhao Applied Mechanics Laboratory Department of Engineering MechanicsTsinghua UniversityBeijing100084China Laboratory of Flexible Electronics Technology Tsinghua UniversityBeijing100084China

The alignment of elongated fibers and thin disks is known to be significantly influenced by the presence of fluid coherent structures in near-wall turbulence(Cui et al.2021).However,this earlier study is confined to the spheroids with infinitely large or small aspect ratio,and the shape effect of finite aspect ratio on the alignment is not *** current study investigates the shape-dependent alignment of inertialess spheroids in structure-dominated regions of channel *** utilizing an ensemble-averaged approach for identifying the structure-dominated regions,we analyze the eigensystem of the linear term matrix in the Jeffery equation,which is governed by both particle shape and local fluid velocity *** contrast to earlier conventional analysis based on local vorticity and strain rate,our findings demonstrate that the eigensystem of the Jeffery equation offers a convenient,effective,and universal framework for predicting the alignment behavior of inertialess spheroids in turbulent *** leveraging the eigensystem of the Jeffery equation,we uncover a diverse effect of fluid coherent structures on spheroid alignment with different particle ***,we provide explanations for both shape-independent alignments observed in vortical-core regions and shape-dependent alignments around near-wall streamwise vortices.

关键词： Non-spherical particle Direct numerical simulation wall turbulence Particle-laden flow

Transient growth in turbulent particle-laden channel flow

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Acta Mechanica Sinica 2020年第1期36卷 1-11页

作者： Yang Song Chunxiao Xu Weixi Huang Lili Wang Institute of Applied Physics and Computational Mathematics Beijing100094China AML Department of Engineering MechanicsTsinghua UniversityBeijing100084China

Linear transient growth of optimal perturbations in particle-laden turbulent channel flow is investigated in this *** problem is formulated in the framework of a Eulerian-Eulerian approach,employing two-way coupling between fine particles and fluid *** model is first validated in laminar cases,after which the transient growth of coherent perturbations in turbulent channel flow is investigated,where the mean particle concentration distribution is obtained by direct numerical *** is shown that the optimal small-scale structures for particles are streamwise streaks just below the optimal streamwise velocity streaks,as was previously found in numerical simulations of particle-laden channel *** indicates that the optimal growth of perturbations is a dominant mechanism for the distribution of particles in the near-wall *** current study also considers the transient growth of small-and large-scale perturbations at relatively high Reynolds numbers,which reveals that the optimal large-scale structures for particles are in the near-wall region while the optimal large-scale structures for fluid enter the outer region.

关键词： Optimal transient growth wall turbulence Coherent structures Particle-laden turbulence