The Scale Characteristics and Formation Mechanism of Aeolian Sand Streamers Based on Large Eddy Simulation

Abstract

Aeolian sand transport near the surface in the field often occurs in the form of sand streamers, which is very important to understand in-depth the physics of aeolian transport and accurately predict the sand transport rate. In this paper, sand streamers were successfully reproduced by combining the Lagrangian trajectory simulation of particles with large eddy simulation of turbulence. The simulated sand streamers are hill-like. Their characteristic scales are extracted by the two-point correlation of sand concentration. It is found that sand streamers corresponding to the correlation threshold of Rcpcp=0.4 are 2.0-4.5 m long and 0.3-0.4 m wide, while 30-100 m long and 1.2-2.4 m wide for Rcpcp=0.05, which are substantially consistent with the existing field observation results and increases with particle size. Conditional averaging method provided an ensemble-mean visualization of flow structures that are responsible for the formation of streamers. It is found that sand streamers on a flat and erodible surface exist in the near-surface wake area of large/very large scale turbulent motions (LSMs/VLSMs), indicating that sand streamers are the footprint of LSMs/VLSMs. Moreover, the characteristic scales of sand streamers will be affected by the splashing process of sand saltation. On a nonerodible surface, sand streamers trailing from upstream sandy surface become narrow though it can propagate downstream for a long distance.