湍流理论的近代发展

这篇论文的内容是关於不可压缩流体的湍流理论近代发展的综合性介绍舆分析。我们首先评述了根据Reynolds的平均运动方程所建立的混合长度理论。其次,分析关於均匀各向同性湍流的主要理论工作。第三,讨论了运用Reynolds的平均运动方程和根据速度涨落方程求得的速度关联函数的动力学方程来处理具有Reynolds剪应力的普通湍流运动问题。同时说明这个方法虽然能够给出比混合长度理论舆实验较为接近的理论结果并能提出速度涨落平方平均值的理论分布,但是由於在求出的速度关联的动力学方程中出现高次元的速度关联,它继续地导致不封闭的微分方程组因而遇到不易克服的困难。因此,从以上湍流理论发展的回顾和最近关於均匀各向同性湍流在后期衰变运动的涡性结构工作,我们在最后提出了对今后湍流理论研究工作的新看法:湍流运动的基本组成部分是流体粘性作用所引起的涡旋运动;这个涡旋运动的动力学根据是用平均的方法后Navier-Stokes方程所导出的Reyonlds的平均运动方程典带度涨落方程。我们并着重说明Reynolds认识到湍流运动可分作平均运动与涨落运动的重要性。今后的理论工作则在於求这两组动力学方程的涡旋运动解,而这种类型的解并须满足像Колмогоров在高Reynolds数运动的局部各向同性湍流理论中所提出的统计条件,方能使解满足惟一性并可舆实验结果相比较。

MODERN DEVELOPMENTS IN THE THEORY OF TURBULENCE

This is a critical exposition and analysis of the modern developments in the theory of turbulent motion of an incompressible fluid. We begin with the review of the mixture length theories based upon Reynolds' equations of mean motion. Secondly, we analyze the principal contributions to the theory of homogeneous isotropic turbulence. Thirdly, we discuss the treatment of the general turbulent shear flow by means of Reynolds' equations of mean motion and the dynamical equations of velocity correlations which are derived from the equations of turbulent velocity fluctuation. We also point out at the same time that although this method yields theoretical results which are in better agreement with experiment than the results of the mixture length theories and furthermore the theory also leads to the theoretical distributions ot the mean squares of velocity fluctuation, on account of the presence of the higher order velocity correlations in the equations, it continuously leads to unclosed systems of differential equations and hence meets difficulties which are difficult to overcome. Therefore, based upon the above retrospect of the developments of the theory of turbulence and the recent work on the vorticity structure of the homogeneous isotropic turbulence in its final period of decay, we finally propose a new approach to the turbulence problem: The basic component motion of turbulence is vortex motion due to the action of viscosity of the fluid. The dynamical equations which govern the vortex motion of turbulence are Reynolds' equations of mean motion and the equations of velocity fluctuation derived from the Navier-Stokes equations by the averaging process. We also emphasize the importance of Reynolds' recognition that the turbulent motion of a fluid can be separated into the mean motion and fluctuation. The future theoretical investigation is to look for the vortex motions which are solutions of these two sets of equations. In order to make the solutions of the problem unique and comparable with experimental measurements, they should also satisfy statistical conditions on the distribution of vortices analogous to Kol-mogoroffs condition in his statistical theory of locally isotropic turbulence at high Reynolds number turbulent flows.