Simulation Of Flow Over An Isolated Barchan Dune

The relationships among sand flux, wind flow and topography are complex and coupled. Studying flow field near the dunes is useful to understand the process and mechanics of dunes formation. And there are only countable papers including detailed analysis about flow over an barchan dune, such as flow acceleration up the stoss slope and what influences separation length in the lee side.This paper simulated flow over an isolated barchan dune with different aspect rations by computational fluid dynamics (CFD) software. In chapter 2, we focus on flow acceleration up with the stoss slope. For example, we analyze the relationships between speed-up factor and dune height, the angle of the stoss slope, wind-speed. And according to these relationships, we derived a formula of the speed-up factor.In chapter 3, we simulate flow over an isolated barchan dune employing commercial software CFD from FLUENT Inc., and discusse how the dune height and upwind speed to influence the separation length, protection length. After we analyzed reverse flow in the lee-side, we proposed that dune height plays a important role in leading to the more extent of the flow acceleration. The increment of wind-speed at the dune crest increases with higher dune. And upwind speed also can influence the increment of the wind-speed up the stoss slope, but comparing with the role of the dune height, this increment is small. Separation length in the lee-side also increases with dune height.In chapter 4, we simulate flow field around a 3D barchan dune, and analyze the relationship between the air flow and sand ripple on the dune surface, and preliminarily discuss the distribution of the shear stress on the dune surface. The results show that there exists apparent acceleration up the side slope, and around the dune. And the shear stress distribution is also very different from the 2D simulation, especially at the horn toe, flow was accelerated apparently.