Aeolian Saltation and Small-Scale Bedform Dynamics in a Large Eddy Simulation Domain

Abstract

In this paper we introduce a setup to investigate aeolian saltation and surface dynamics on a centimetre spatial resolution and a sub second temporal resolution. We develop a Lagrangian saltation model and a high-resolution surface model, which we couple to each other and to a turbulence resolving large eddy simulation model. The simulated transport takes place primarily in the form of aeolian streamers, bursts of elongated transport structures parallel to the wind field, which result in a mass flux signal that is highly heterogeneous both in space and time. The temporal frequency responses up to 1 Hz of the mass flux and wind field share the same characteristics, which indicates a coupling between the two. The system can be in equilibrium, during which the stress profiles induced by the particles, the turbulent fluxes and the imposed large scale pressure gradient balance each other. A bimodal shape is found in the mass flux profile, in which we can distinguish an upper and lower saltation layer. The upper layer is associated with a transitional phase between transport by saltation and suspension that exists in the aeolian streamers. Furthermore, The setup is able to simulate ripples, although future research is needed to investigate the mechanisms that influence the final shape of the ripples.