The Influences Of Different Bedforms On Wind-Blown Sand Movements

In order to simulate the effect of different boundaries on wind-blown sand flow, this thesis deals with the particle motions in air under the consideration of different bedforms by using self-developed computer program. Firstly, the flow around a circular cylinder is simulated to verify the reliability and validity of the program. In order to simulate the real properties of flow around two-dimension cylindrical body, and also to analysis the wake vortex, discrete forms of the large eddy simulation of continuity equation and motion equations have been performed in chapter 2. At the same time, in order to guarantee the convergence of the algorithm, SIMPLER method is applied. Based on the simplification of actual situation, numerical simulation method for accurate analysis is used, then the flow patterns among different Reynolds number were obtained. Particularly, some numerical results are compared with those in literature, it is shown that LES method is reliable and useful in 2D wind-blown sand movement.Secondly, the thesis works out the development of velocity profile for flow field around sand ripples with various lengths and widths under different Reynolds numbers, which is based on the change of flow field's structure with different space distances. The developing tendency for the peak of the sand ripple flow field and for the separation and reflux positions behind the sand ripple have been studied. For the case in which there is only one unsymmetrical sand ripple, the thesis obtains the velocity profiles at different positions under the circumstance, and then analyses are carried out.At last, to study the motion of wind-blown sand near sand ripples surface, large eddy simulation method and SIMPLER algorithm are employed. First, based on the flow field near the boundary calculated in previous sections, the paper simulates the trajectories of sand particles with the same diameters, and also the thesis calculates the relationship between sand saltation length and the geometrical sizes of sand ripple which represents the real word of wind-blown sand movement with considering the influence of different sand bedforms. The work in this thesis is of important value in sand landforms.