野外近地表风沙流脉动特征分析

Fluctuating of Wind-blown Sand Flux in Field Wind Condition

基于风沙流实时测量系统对流沙地表的输沙强度以及不同高度风速进行实时测量所获得的数据,分析野外实际风场中的风沙流脉动特征。结果表明:沙粒的存在削弱平均流场,但对风速的高阶统计矩和分布形式影响不大,不同高度、不同来流平均风速条件下,风沙流中风速仍近似符合高斯分布;瞬时输沙强度服从指数分布,滞后风速约1s,脉动强烈;30min输沙强度平均值和脉动标准差均随平均风速的增大而呈幂函数增加,但随风速脉动强度的变化呈先增大后减小的趋势。这意味着脉动风速对输沙率具有重要影响,需要在输沙率预测公式中予以考虑。

This paper analyzes the fluctuating characteristics of windblown sand flux on the basis of the data acquired from the realtime measurements of wind velocity and saltation intensity by the measurement sys tem. The results show that sand saltation reduces the mean wind velocity, but it has little influence on high er order statistical moments and probability distribution of wind series. Wind velocity in drifting sand ap proximately accords with Gaussian distribution under different heights and different mean wind velocities. Instantaneous saltation intensity obeys exponent distribution and is roughly 1 s late to the wind speed, and the fluctuation is fierce. As the average wind velocity increase, the average saltation windblown sand flux in 30 rain intervals and its fuctuation augment in the form of power function. But with the change of the wind fluctuation, the average saltation windblown sand flux augments at first, then minishes. It indicates that the fluctuation of wind velocity is essential to saltation windblown sand flux and should be taken into consideration in prediction formula of transport rate.