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Scale properties of turbulent transport and coherent structure in stably stratified flows

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Applied Mathematics and Mechanics(English Edition) 2016年第4期37卷 443-458页

作者： Long ZHU Xiang QIU Jianping LUO Yulu LIU School of Mechanical Engineering Shanghai Institute of Technology School of Science Shanghai Institute of Technology Shanghai Institute of Applied Mathematics and Mechanics Shanghai University

The empirical mode decomposition （EMD） is used to study the scale properties of turbulent transport and coherent structures based on velocity and temperature time series in stably stratified turbulence. The analysis is focused on the scale properties of intermittency and coherent structures in different modes and the contributions of energy-contained coherent structures to turbulent scalar counter-gradient transport （CGT）. It is inferred that the velocity intermittency is scattered to more modes with the development of the stratified flow, and the intermittency is enhanced by the vertical stratification, especially in small scales. The anisotropy of the field is presented due to different time scales of coherent structures of streamwise and vertical velocities. There is global counter-gradient heat transport close to the turbulence-generated grid, and there is local counter-gradient heat transport at certain modes in different positions. Coherent structures play a principal role in the turbulent vertical transport of temperature.

关键词： stratified turbulence coherent structure counter-gradient transport （CGT）,empirical mode decomposition （EMD）

TURBULENT MIXING AND EVOLUTION IN A STABLY stratified FLOW WITH A TEMPERATURE STEP

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Journal of Hydrodynamics 2009年第1期21卷 84-92页

作者： QIU Xiang ZHANG Dao-xiang LU Zhi-ming LIU Yu-lu Shanghai Institute of Applied Mathematics and Mechanics Shanghai University Shanghai 200072 China Department of Mathematics Shanghai University Shanghai 200444 China

Large-Eddy Simulation （LES） is applied to examine the turbulent mixing and evolution in a stably stratified flow with a thermally sharp interface. Turbulent velocity intensities and turbulent kinetic energy are analyzed by considering the mean shear and stratification effects. The evolution of turbulent mixing layer and turbulent structures are mainly investigated. The results show that the streamwise intensities are much larger than the vertical intensities, and vertical fluctuations decay more rapidly at the presence of stratification. The qualitatively computational results suggest that the mixing layer, defined by the mean temperature, inclines to the side with small inlet velocity. The evolution of the half-width of the mixing layer shows two different slopes. The turbulent structure with high vorticity is restricted in the mixing layer especially in strong stratified cases.

关键词： stratified turbulence turbulent mixing turbulent structure Large-Eddy Simulation （LES）

AN INVESTIGATION OF TURBULENT HEAT TRANSFER IN CHANNEL FLOWS BY LARGE EDDY SIMULATION

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Journal of Hydrodynamics 2002年第2期14卷 29-35页

作者： Dong Yu-hong, Zhong Feng-quan, Lu Xi-yun, Zhuang Li-xian Department of Mechanics and Mechanical Engineering, University of Science and Technology of China, Hefei 230026, China Dept. of Mech. and Mech. and Eng. Univ. of Sci. and Technol. of China Hefei 230026 China

Large Eddy Simulation (LES) of fully developed turbulent channel flow with heat transfer was performed to investigate the effects of the Reynolds number on the turbulence behavior. In the present study, the bottom wall of the channel was cooled and the top wall was heated. The Reynolds numbers, based on the central mean-velocity and the half-width of the channel, were chosen as 4000, 6000, 10 4 and 2×10 4, and the Prandtl number as 1.0. To validate our calculations, the present results were compared with available data obtained by Direct Numerical Simulation (DNS), which proves to be in good agreement with each other. To reveal the effects of the Reynolds number, some typical quantities, including the velocity fluctuations, temperature fluctuation, heat fluxes and turbulent Prandtl number, were studied.

关键词： Large Eddy Simulation (LES) turbulent channel flow Subgrid Scale (SGS) model heat transfer stratified turbulence

Large eddy simulation of turbulent statistical and transport properties in stably stratified fows

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Applied Mathematics and Mechanics(English Edition) 2009年第2期30卷 153-162页

作者：邱翔黄永祥卢志明刘宇陆 Shanghai Institute of Applied Mathematics and Mechanics Shanghai University Department of Mathematics School of Sciences Shanghai University

Three dimensional large eddy simulation （LES） is performed in the investigation of stably stratified turbulence with a sharp thermal interface. Main results are focused on the turbulent characteristic scale, statistical properties, transport properties, and temporal and spatial evolution of the scalar field. Results show that the buoyancy scale increases first, and then goes to a certain constant value. The stronger the mean shear, the larger the buoyancy scale. The overturning scale increases with the flow, and the mean shear improves the overturning scale. The flatness factor of temperature departs from the Gaussian distribution in a fairly large region, and its statistical properties are clearly different from those of the velocity fluctuations in strong stratified cases. Turbulent mixing starts from small scale motions, and then extends to large scale motions.

关键词： stratified turbulence turbulent mixing turbulent transport turbulence structure

Large Eddy Simulation of stratified Turbulent Channel Flow with a Dynamic Subgrid Scale Model

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Advances in Manufacturing 2000年第2期4卷 87-91页

作者： Feng-quan Zhong Nan-sheng Liu Xi-yun Lu Bing-gang Tong Department of Mechanics and Mechanical Engineering University of Science and Technology of ChinaHefei Anhui Province 230026 China

In this paper, large eddy simulation coupled with a dynamic subgrid scale (SGS) model is used to study turbulent channel flows with heat transfer. Some fundamental flow behaviors are discussed. Based on our calculated results, the dynamic SGS model can reasonably predict some main characteristics of stratified turbulent channel flows. Our results are also in good agreement with theoretical analyses and previous calculated results.

关键词： large eddy simulation (LES) subgrid scale (SGS) model stratified turbulence heat transfer