Numerical modelling of saltation in the atmospheric surface layer

A numerical model is developed to study the hopping motion of sand grains ( saltation) in neutral atmospheric surface layers. Saltation is considered a s a self-limiting process governed by the interaction of four components: a erodynamic entrainment, particle motion, splash entrainment and wind modifi cation. The model comprises a large eddy simulation model for atmospheric s urface-layer flows, a Lagrangian model for particle trajectories and a stat istical description for aerodynamic entrainment and splash entrainment. The numerical simulation is focused on the aspects of saltation that are not w ell understood from experimental studies, including the role of splash, the evolution of wind and momentum flux profiles, and the effective roughness length, z(0)s. It is shown that for splash to be effective, the surface fri ction velocity must exceed a critical value for a given particle size. The numerically estimated z(0s) is compared with the analytical model of Raupac h and the experimental data of Gillette et al. The model is also used to ca lculate the streamwise sand drift and the numerical results found to be in agreement with the existing wind-tunnel measurements.