一阶湍封闭的某些改进

应用 Prandtl混合长理论导得既包含梯度项又包含二阶导数的湍流通量闭合方案 ,并进一步分析了该封闭方案用于湍流扩散方程的数值解行为。分析表明 :(1)扩散项使污染物扩散并趋于空间均匀分布 ,而频散项导致污染物空间分布非均匀 ;(2 )所给出的改进后的一阶湍流封闭方案既可解释标量物质的局地反梯度输送现象又可能使 K理论用于混合层。

Some Improvement in First Order Closure Scheme for Turbulent Diffusion

A modified first turbulent closure scheme is derived based on Prandtl mixing length theory, and a consequential turbulent diffusion equation which contains not only a diffusion term but also a dispersion term is developed. The preliminary studies in this paper emphasize the contribution of counter gradient transportation to the spatial inhomogeneous distribution of property concentration distribution. The results of simple numerical simulation of the newly derived turbulent diffusion equation show that (1) turbulent diffusion makes the concentration spatially homogeneous but turbulent dispersion results in inhomogeneous spatial distribution. (2) The local counter gradient transportation phenomena of property in turbulent shear flow can be expressed by utilizing the modified first turbulent closure scheme in the paper, furthermore, the closure scheme may make the K theory available in CBL.