Large-eddy Simulation Of Three Dimensional Turbulent Aeolian Motion And Numerical Simulation Of Evolution Of Sand Ripples

In this thesis, numerical simulation of three dimensional turbulent aeolian motion and the formation of sand ripples under three dimensional turbulent wind are carried out. The main work and resuls are as follows:A large-eddy simulation program for three dimensional aeolian motion and sand ripples under three dimensional turbulent wind is obtained, which combines the three dimensional pseudo-spectrum method and the method of immersed boundary and models of three dimensional aeolian motion. The reliability and verification of the code is vertified with the trajectory of single particle and the sand flux per width with others numerical and experimental results.In the motion of single particle, we analyze the trajectories in one-way model when different force act on single particle, and discuss the influence of each force on trajectories of particle, the results show that gravity and aerodynamic drag are the most important forces, electrostatic force play a more important role than lift force. The influence of Magnus force is determined by the angular speed of particle, therefore when the angular speed is small, the influence can be neglected. Because the partcles obstructs the wind, so that the saltation length of single particle obtained by the one-way model is slightly larger than that of by the tow-way model.In the motion of large amount of sand particles, electrostatic force plays a more important role than lift force in the average velocity of particles and the structure of aeolian motion. The average velocity of particles in Y direction is hardly affected by the force in Z direction, even this force is quite large. Furthermore, we find the aeolian sand flow is divided into three layers: linearly increasing layer, saturation layer and decrease layer, according to the amount of transportation of sands, which is agreed with experimental results.The evolution process of three dimensional sand ripples is obtained, with the models of saltation and creep, the resulting form of sand ripples has the feature of sand ripplrs in the nature, i.e., the slope of lee side is steeper than the slope of up-wind side. Furthermore,...