The Influence Of The Particles'mid-air Collision On Wind-blown Sand Saltation

Sand movement under wind flow is one important physical process of wind erosion and sand/dust storms, which have severely impacted the natural environment and human activity. In recent years the disasters due to the wind-blown sand movement have being devoted much attention in China. It is considered crucial to profoundly study the wind-blown sand movement mechanism for overall understanding and preventing wind-blown movement and scientists have done a lot of work on it. However, many former scholars had not taken account of the influence of saltating particle' mid-air collision when they calculate the sand transport rate of saltating particle. The mid-air inter-particle collision generally is neglected in aeolian saltation because it is a stochastic and complex process.In order to exactly estimate the probability of a mid-air inter-particle collision for a saltating particle in a steady-state saltation cloud, a physical model that can predict this probability is developed based on the models of Sorensen and McEwan (1996) and Zhang Yali (2005). In our model, a set of experimentally determined saltation cloud wind profiles, which are notably non-logarithmic, are employed. The results show that, compared with the result of the mid-air collision probability in logarithm wind speed, the collision probability obtained with experiment wind velocity is smaller than the one with logarithm wind speed.Finally, a simple model, which is used to calculate saltating particles' velocity diversity in mid-air collision, is set up through hard ball model .Combining with the model of collision probability, saltating particle' sand transport rate which varies with height and mass flux which varies with friction velocity are calculated in mid-air collision. Compared with the result when mid-air collision is not considered, it suggests that the diversity is less than that of this thesis. So is the diversity of mass flux with friction velocity. In the meantime, the results show that the mid-air inter-particle collision has obvious effects on wind-blown sand saltation. Therefore, the influence of saltating particle collides in the midair can not be ignored when studying sand transport rate of saltating sand.