Statistical behaviors of different‐sized grains lifting off in stochastic collisions between mixed sand grains and the bed in aeolian saltation

Multiple‐size splash models are derived from the simulation results of mixed grain‐bed impact process of windblown sand flow based on the Particles Dynamics Method (PDM) and parallel algorithm. Unlike previous studies, a probability density distribution of sand diameter is considered in the present study, in which a two‐dimensional mixed sand bed is generated by a random method. After the diameter distribution of incident grains is divided into n subregions of representative diameters, first, the collisions are simulated out for each representative diameter of incident grains with an incident velocity impacting the mixed sand bed, to which the information of grains experiencing saltation liftoff may be gained at the end of collisions. After that, a statistical approach is proposed to obtain the average values of velocity and number of the ejecting and rebounding grains as well as the probability density function (PDF) of ejection particle sizes. The results confirm earlier findings that the ratio between outgoing and incoming speed remains about 60% and the ejection angles are typically between 60–80°. However, other properties of grains experiencing saltation liftoff depend not only upon incident velocity as previously argued, but also much upon grain size of incident grains. We found that rebound angle decreases and death rate of incident particles increases with incident grain size exponentially, and ejection speed and number increase logarithmically with both speed and diameter of incident grains. In addition, the PDF of initial diameter is also presented for the first time. These results well agree with the multiple‐size measurement data.