Turbulent Elementary Votrices and New Development in Theory, Predicition, and control of Turbulence

基本涡是湍流中最小的相干结构。它们在湍流中的物理特性和动力学作用已通过理论、实验和计算机模拟在自然界、实验室和计算机上实现的各种湍流中得到阐明。基本涡具有与湍流类型无关的共同物理特征，即中心涡为螺旋涡层所包围，涡的直径和速度服从Kolmogorov标度律，涡的长度向湍流大尺度延伸，涡在空间上成团并局部化，并且许多基本涡倾向于以反平行方式接近并增强混合能力。在工程应用方面，建立了基于基元涡的大涡模拟模型，通过控制基元涡实现壁面湍流的主动反馈控制，阐明了纵向涡的引入对超声速混合燃烧的强化作用和大尺度拟序涡产生龙卷风的机理。此外，在Couette湍流中还发现了伴随着基元涡再生的不稳定周期运动（时空相干结构是湍流的骨架）。本研究所建立的湍流基元涡的概念和动力学特性对今后的湍流研究具有一定的参考价值。

The elementary vortices are the smallest coherent structures in turbulence. Their physical characteristics and dynamical roles in turbulence have been clarified by the theory, the experiment, and the computer simulation in various kinds of turbulence realized in nature, laboratories, and computers. The elementary vortices exhibit common physical characteristics independent of the kinds of turbulence, that is, a tubular central vortex is surrounded by spiral vortex layers, the diameter and swirl velocity obey the Kolmogorov scaling laws but the length of the vortex extends to the large scales of turbulence, the vortices make groups and are localized in space, and many elementary vortices tend to approach in an anti-parallel manner and enhance the mixing ability. As engineering and practical applications, the large-eddy-simulation model based on the elementary vortices, the active feedback control of the wall turbulence by manipulating the elementary vortices have been developed, and the mechanisms of the enhancement of supersonic mixing combustion by introducing the longitudinal vortices and the generation of tornados as the large-scale coherent vortex have been clarified. Furthermore, the unstable periodic motions (spatio-temporal coherent structure as the skeleton of turbulence) accompanying regeneration of elementary vortices have been discovered in the Couette turbulence. The concept and the dynamics of turbulent elementary vortices established in the present research project shall be useful for the future turbulence research.