A Similarity Theory for Heterogeneous Saltation

摘要

In saltation theory, it is often assumed that saltating particles are uniform in size and follow identical trajectories. In this paper, we study heterogeneous saltation, i.e., the saltation of multi-sized particles in turbulent flows. A theory for saltation similarity is developed, which deals with the variation of particle size distribution with height, the entrainment rates of particles in different size ranges and the profiles of saltation flux, particle momentum flux and particle concentration. To derive the theory, a stochastic saltation model is applied to simulating particle motion. The numerical results are fitted to similarity functions. We show that the profile of saltation flux, q(z), is determined by friction velocity, aerodynamic roughness length and soil particle size distribution. Measurements of streamwise saltation flux of 32 particle size groups are made at Qira using a sand particle counter, together with measurements of wind and other atmospheric variables. These data are used to validate the theory.