均匀剪切湍流中不同尺度结构相互作用及输运机理研究

剪切湍流中蕴含丰富的多尺度、多形态的流动结构，而这些流动结构的演化主导着湍流的级串和输运过程，是湍流机理研究的关键。均匀剪切湍流（与壁湍流相比）因其不受固壁面的影响，也不存在非均匀剪切效应，是深入研究剪切湍流机理的一类理想流动。本课题主要采用实验测量和直接数值模拟方法，发展基于数据挖掘和机器学习的湍流结构高效识别、分类和提取方法，研究均匀剪切湍流中大尺度结构产生、发展、衰减和再产生过程中的时空演化动力学特性及其与壁湍流的异同；建立均匀剪切湍流中正反发卡涡和发卡涡团簇等拟序结构的动力学模型；定量刻画大尺度结构时空演化，特别是均匀剪切湍流中特有的反发卡涡演化对均匀剪切湍流级串、逆级串过程，输运、逆梯度输运的作用。课题研究成果不仅能深化对剪切湍流物理机制的认识，而且能为实践中调控湍流结构和湍流输运提供理论支撑。

There exist a variety of multi-scale and multi-shape coherent structures in shear turbulence. The spatial and temporal evolution of turbulence structures which dominates the cascade and transport in shear turbulence, is the key ingredients of the fundamental research of turbulence. This project aims to study both experimentally and numerically the generation, development, decay and regeneration processes of multi-scale turbulence structures in homogeneous shear turbulence. Compared to the complexity of wall effects and inhomogeneous shear in wall turbulence, homogeneous shear turbulence is an ideal flow to be used to study the turbulence mechanism of shear flows. A novel data-driven method based on the machine learning technique is to be developed for the identification and classification of turbulence structures, and a special dynamic model for the coherent structures is to be built for homogeneous shear turbulence. Special attention will be paid on the quantitative description of the effects of these multi-scale turbulence structures including both upright and inverted hairpins on cascade (negative cascade) and gradient (counter-gradient) transport process in shear turbulence. This study is of significance to the comprehensive understanding of the shear effects on turbulence and may provide some new insights to the modulation of turbulent structures and turbulent transport in engineering.