A three‐dimensional analysis on lift‐off velocities of sand grains in wind‐blown sand flux

Abstract

AbstractThis paper focuses on a key problem in wind‐blown sand transport research, the lift‐off velocities of sand grains. A three‐dimensional grain‐bed collision model comprising an impact sand grain, a creeping sand grain and a sustaining grain is presented. Based on this model, the analytical formulae of sand grains' linear and angular velocities are derived. The rebound/ejected coefficient (ratio of rebound/ejected velocity to impact velocity) and angle are numerically calculated using the analytical formulae and they agree well with the experiment results, which indicates that the three‐dimensional model is credible and necessary. Comparisons of our results with the results gained by a two‐dimensional grain‐bed collision model show that all components of both rebound and ejected velocities gained by the three‐dimensional model are lower than the corresponding ones done by two‐dimensional model apart from the horizontal rebound velocity. It also shows the lateral velocity and the lateral angular velocity, as well as the upward angular velocity, cannot be obtained by a two‐dimensional model, and cannot be ignored when the impact velocity is high. Copyright © 2008 John Wiley & Sons, Ltd.