风沙流中颗粒运动参数的分布特征

Statistics of Particle Saltation Process in Air Flows

以风洞内颗粒高速摄影实验资料为基础 ,对颗粒跃移运动参数的分布及其跃移速度分布函数进行了探讨。研究结果表明 ,颗粒跃移的相对高度和相对长度的分布都不呈正态分布 ;降落角大致成正态分布 ,而起跃角则为非正态分布 ;颗粒起跃时水平速度 ,垂直速度和合速度的分布都呈非正态分布 ;随着跃移高度的增加 ,颗粒的平均粒径减小。速度分布函数是描述颗粒跃移统计特征的有效工具 ,具有修正指数形式或修正正态分布形式的概率密度分布函数都能较好地描述跃移颗粒的速度分布状况。

Statistical data are presented from high-speed films of sand grain saltating in a wind tunnel. The results indicate that the frequency distributions of saltation trajectory heights and lengths normalized on their mean values disagree with normal distribution. The frequency distribution of impact angle is normal distribution, while ejection angle is not. The frequency distributions of ejection velocity components including horizontal and vertical velocities aren't normal distributions. The particle size decreases with saltation height. The function of velocity distribution of particle is valid for statistical characteristics of particle saltation, and a revised exponent or normal distribution can be useful in expressing grain ejection.