不同湿度下的云雾-不饱和空气湍流混合实验研究

Experimental study of turbulent mixing of the cloud with unsaturated air under different humidity

本实验设计建造了一个80×80×100cm3的室内云雾腔,对不同环境湿度下的云雾-不饱和空气混合过程的湍流特征进行了实验研究,利用PIV技术,获得了混合过程中的速度场,得到了湍动能、脉动速度二阶结构函数、泰勒微尺度等物理量。结果表明:该实验测得的湍流泰勒微尺度为mm量级;云雾-不饱和空气混合过程的脉动速度场表现出明显的各向异性,随着不饱和环境湿度的增加脉动速度概率密度函数在尾部越来越偏离标准高斯分布;横向结构函数和纵向结构函数比值明显偏离基于均匀各向同性湍流的理论值。

This paper presents PIV results of turbulent mixing of the cloud and unsaturated air with different environmental humidity in a small cloud chamber （80 × 80× 100cm3）. Turbulence characteristics such as the variation, skewness and flatness factors of two-dimensional velocities are first calculated to demonstrate the anisotropy of such turbulent fields of several centimeters scale. Experimental results further show that the departure of the probability density function（PDF） of the vertical velocity component from the standard Gaussian distribution be- comes more obvious at the tails with the increase of unsaturated environmental humidity. The anisotropy of the turbulence is further revealed by the difference between the second-order structure functions of two velocity components. The isotropic ratio （the ratio of transverse structure functions to longitudinal structure functions） is far different from the theoretical value for homogeneous and isotropic turbulence and its dependence on the environmental humidity is complicated and needs further investigation.