高雷诺数湍流中相干结构的自维持、自相似及其控制

It is of great importance to understand the self-sustaining and self-similarity of the coherent structures at high Reynolds number turbulence, since this is helpful for explaining new phenomenon in turbulence and for proposing new practical control strategies. The applicant of the current project recently discovered a new family of self-similar exact coherent states at high Reynolds number turbulence, which remarkably resembles Townsend’s attached eddies. Starting from this point, the current project wants to extend these exact coherent states to a wider parameter space, and get a deep analysis of their self-sustaining process and self-similarity. Together with the other two techniques, i.e. conditional average in large scale turbulence channels, and dynamics analysis of narrow domain turbulence channels, the project expects to get a new understanding on some fundamental issues on turbulence, such as the characteristic length scales of coherent structures, scale interactions, energy cascade, the self-sustaining process at Kolmogorov microscale etc. Based on this, we further study the effect of streamwise travelling wave of spanwise wall velocity on turbulence coherent structures. With the combined approaches of full scale turbulence channels, narrow domain turbulence channels and exact coherent states, we aim to explore the drag reduction mechanism and understand the reason for drag reduction deterioration at high Reynolds numbers, thus providing guides for practical drag reduction applications in Engineering.

理解高雷诺数湍流中相干结构的自维持、自相似对于揭示湍流中新的规律现象、提出工程适用的湍流控制策略具有最要意义。项目申请人最新发现了高雷诺数湍流中的一族自相似的精确相干态，与Townsend的附面涡模型有惊人的相似处。本项目欲以此为起点，将此精确相干态在更广泛的变量空间内进行延拓，并深入挖掘其自维持、自相似等特性。结合全尺度槽道湍流的条件平均、窄槽道湍流的动力演化，期望对湍流中的相干结构的特征尺度选择、不同尺度间干扰、能量级串、Kolmogorov微尺度下自维持等基本问题形成新的理解。在此基础上考察壁面展向速度诱导流向行波与湍流相干结构的相互作用，利用全尺度槽道、窄槽道和精确相干态三种方法联合分析减阻的机理及弄清高雷诺数湍流壁面减阻控制效果恶化的原因，为实际工程减阻应用提供指导。

高雷诺数湍流广泛地存在于自然界和工业界，相对于层流状态，湍流具有复杂的动力学特征，且摩阻要提升3-5倍，大大增加了交通运输工具的能源消耗。本项目从非线性动力系统的角度研究了湍流的两个重要特征，即自相似和自维持过程，获得了具有粘性标度率的精确相干态，提出了适用于高雷诺数湍流预测的广义准拟线性近似模型（GQL），并基于此工具开展了大量数值实验发现了湍流中低、高波数区的能量传递及尺度相互作用的具体影响过程。同时从湍流减阻和转捩推迟的角度出发，研究了展向壁面振动控制和粗糙元被动控制，在国际上首次获得了非定常控制力作用下的精确相干态，从系统分叉的角度回答了最优控制参数的由来以及减阻机理。最后提出了基于等离子体发生器阵列的展向壁面振动布局，有望在今后获得湍流减阻的工程应用。