Effects of Shape and Rotation of Sand Particles in Saltation

Abstract

Eolian sand transport is a typical gas-solid flow process, and saltating sand particles account for 75% of the total sand transported. Sand particles are considered as perfect spheres, and the forces acted on the particles are calculated using concise formulas in almost all wind-sand movement models. In fact, most of sand particles in natural environment are nonspherical and usually rotating while they saltate in the air, and the complicated turbulent gas-solid flow caused by irregular shape and rotation of particles cannot be predicted. In this paper, the microcosmic midair movements of rotating elliptical sand particles are simulated with dynamic grid method, and the interaction between airflow and sand particles is studied. The results show that the trajectory of a rotating elliptical particle is 18.8% higher and 31.8% longer than that of a spherical one and the drag force acted on a rotating elliptical sand particle fluctuates periodically over time. Separating, colliding, and tumbling behaviors are observed during the saltation process of coupled sand particles. Affected by strong interaction between rotating coupled elliptical particles and airflow, the trajectory is 8.4% lower than one particle system, and the rotation decreases the midair colliding behaviors. A parametric scheme for drag coefficient of sand particle is summarized to modified the macroscopical Eulerian-Lagrangian wind-sand simulation, in which the saltation transport rate varies for different shapes of sand particles. This work indicts that an accurate prediction of shape and rotation effects is required to describe the sand movement and saltation transport.