Cellular model for sand dunes with saltation, avalanche and strong erosion: Collisional simulation of barchans

摘要

Barchans are crescent-shaped dunes that form under unidirectional wind in areas of limited sand supply. The recent development of flume experiments and computer simulations has renewed interest in the interaction dynamics of two or more barchans. From the flume experiment, four distinguishable types of collision patterns between two barchans have been observed: coalescence, ejection, split and reorganization. We have proposed a simple cellular model for numerical simulations of dune dynamics, in which saltation and avalanche are elementary processes. In the present paper, we first describe the model in detail. The model reproduces three types of collision patterns: coalescence, ejection, and reorganization. The largest reason for a split pattern not to occur is the lack of an effect of the flow separation at the brink line of dunes and the recirculation bubble that it produces. We then model the effect of the recirculation bubble by assuming that strong erosion occurs at the reattachment point of the separation flow. The strong-erosion model successfully reproduces all the collision patterns. Thus, three elementary processes - saltation, avalanche and strong-erosion - are sufficient for a phenomenological description of the interaction dynamics of aqueous barchans. It is also shown that the type of collision is determined by competition between the filling-up of the interdune between two barchans and the change in height of each dune.