Numerical investigation on two-grain-bed collisions in windblown sand transport

Abstract

Grain/bed collisions play a significant role in the transportation of granular materials, especially in windblown sand movements. In this study, grain/bed collisions regarding two sand grains simultaneously impact onto a mix-sized sandy bed are numerically investigated by the discrete element method (DEM). Results demonstrate that even under the same initial conditions, the outcome of two sand grains simultaneously impacting a 2D sand packing (termed as two-grain–bed collisions) is different from the superposition of two grain/bed collision events (termed as twice grain–bed collisions). Analysis show that when the windblown sand concentration is higher than a critical concentration Q cr , the number of ejected sand grains given by twice grain–bed collisions is 23% higher than that by two-grain–bed collisions. Therefore, two-grain–bed collisions considering the interaction of two grains simultaneously impact a sand-bed is a significant factor that cannot be overlooked in numerical schemes of windblown sand flux. The ejected number of two sand grains simultaneously impacting the sand-bed (case A ) is different from the superposition of two grain/bed collision (case B ). In the case B , the L/d has an effect on the ejected number. When the distance L between the two impacting sand grains is long enough, the interaction effect of simultaneous collisions can be ignored. ► We conducted numerical simulations of two-grains-bed collisions. ► Results of two-grains-bed collisions and twice grain-bed collisions are compared. ► The distance of the two simultaneously impacting grains has effect the outcomes. ► We present a formula of the critical distance as a function of impact velocity.