Simulation of the probability of midair interparticle collisions in an aeolian saltating cloud

Abstract

Midair interparticle collisions in aeolian saltation are generally neglected because they are considered to be rare. A theoretical simulation model was developed to calculate the probability of these collisions for uniform‐sized sand. The collision probabilities during the ascending and descending stages and during the whole saltation process are calculated for saltating particles with different liftoff velocities and at different free‐stream wind velocities on the basis of data for particle concentrations in the saltating cloud. The collision probability is also calculated on the basis of the probability distribution for liftoff velocities. The calculated probabilities reveal that midair collisions should not be neglected. They increase in frequency with increasing free‐stream wind velocity and liftoff velocity and are nearly inevitable at high wind velocity. The collision probability is greater during the descending stage than during the ascending stage. Steady state saltation is maintained by feedback between the air stream and the saltating particles and between surface impacts and midair collisions. Increased surface impacts increase sand transport and the probability of midair collisions, but increased midair collisions may reduce surface impacts and sand transport. The feedback between surface impacts and midair collisions becomes more significant as wind velocity and sand transport increase.