风沙流的输沙率沿程变化规律

Evolution of Streamwise Sand Transport with Distance

将风力作用下的地表侵蚀分解为气流直接侵蚀和跃移沙粒冲击侵蚀两个部分,在冲击侵蚀率中考虑颗粒与床面之间以及颗粒之间碰撞影响的前提下,结合地表蚀积平衡方程从理论上导出了风沙流的输沙率沿程变化公式。公式的预测值与实测资料吻合较好。以该公式为基础,进一步得到了流体侵蚀率、冲击侵蚀率和总侵蚀率各自沿程的理论变化表达式以及饱和路径长度公式,并且发现流体侵蚀率沿程逐渐减小,而冲击侵蚀率和总侵蚀率沿程变化规律都是开始时增大、然后减小,存在极大值;流体侵蚀累积量在总累积侵蚀量中所占的比例并不是固定不变,而是随气流速度的增大而增大。

A simple theoretical expression for evolution of streamwise sand transport with distance was put forward. Wind erosion is consisted of two parts, fluid erosion and impact erosion. Fluid erosion is induced by the force of airflow directly exerted on the bed while impact erosion results from the impaction of saltating grains on the bed. The former depends on the difference between local and saturation sand transport rates, while the later is merely associated with the local sand transport rate. An analytic expression for sand transport rate with distance was deduced by introducing two parts of wind erosion into the continual equation of erosion. Prediction from the expression was compared with the measurement in the wind tunnel, and satisfactory agreement was achieved. Based on the expression, two erosion rates with distance, fluid and impacting erosion rates, were deduced. Fluid erosion rate decreases with distance while impacting one firstly increases and then decreases with distance. Also, an expression of saturation length of sand transport was introduced.