湍流的相干结构:推演方法和结果

本文讨论壁面湍流发展的相干结构的观点.在简要的历史文献综述后,我们回顾一些基本观点,并且介绍相干结构的思想.基于大量主要是由实验所得的结果,本文通过广泛运用的事件检测技术,探讨湍流边界层内部和外部区域发生的现象.我们从边界层内部区域发生的现象、边界层外部大尺度运动的发展和涡结构动力学的角度来描述流动的现象.在文章的第2部分,介绍从背景流动中推演出湍流相干结构的各种方法以及在各种方法框架下所得到的结果,讨论速度梯度张量不变量、压力的Hessian矩阵分析和本征正交分解等方法.每一个过程都有``相干结构'的特定的定义,满足恰当的数学构架,并可以对湍流数据做相干结构动力学分析.这一工作可能会对当前流体动力学家在湍流研究中用到的最新理论和技术的传播有所贡献.

COHERENT STRUCTURES OF TURBULENCE: METHODS OF EDUCTION AND RESULTS

In this paper the issue of the coherent structures of turbulence developing in wallbounded flows is addressed.After a short historical synthesis,some basic concepts are reviewed and the idea of coherent structure is introduced.The phenomena occurring in the inner and outer regions of the turbulent boundary layer in conjunction with the most widely used event-detection techniques are considered,with reference to the large amount of mainly experimental results existing on the subject.The flow phenomena are described in terms of events occurring in the inner region,large-scale motions developing in the outer layer and dynamics of vortical structures.In the second part of the paper,methods for the eduction of the coherent structures of turbulence from the background flow and results obtained in the framework of each method are presented.The techniques involving the invariants of the velocity gradient tensor,the analysis of the Hessian of the pressure and the proper orthogonal decomposition are considered.Each procedure involves a particular definition of coherent structure that is supported by an appropriate mathematical framework and permits the analysis of a turbulent- flow database in terms of dynamics of coherent structures.This work may contribute to the dissemination of the most recent concepts and techniques now in use in turbulence research among fluid dynamicists.