Numerical Research On Several Problems In Windblown Sand Saltation

Desertification is a fatal environmental problem, which is caused by the movement of sand under the wind field. Moreover, windblown sand movement is the main cause of soil erosion and dust storms. So, the research on the characteristics of windblown sand movement is one of the important issues concerning the windblown sand physics and the sand control project. Based on the theoretical model of particles in the coupled wind-sand-electricity fields, the forces acting on the saltating sand particles are analyzed and the trajectory characteristics of saltating particles and mass flux in the fluctuating wind field are numerically simulated. The main achievements made in this paper are as follows:1. Through numerical simulation of the saltation in the coupled wind-sand-electricity fields under the steady wind field, this paper analyzes the forces acting on saltating particles. Furthermore, the laws of above forces varying with the initial angular velocity, lift-off velocity, friction wind velocity and the diameter of the particles are discussed. The results show that, in sequence of the intensity of effect on the motion of saltating particle, they are aerodynamic drag, gravity, electrostatic force, Magnus force and Saffman force from strong to weak in order. The aerodynamic drag force is generally greater than the gravity, and even several times as much as the gravity. The electrostatic force is more than 20% of gravity. The Magnus force is about 10%-70% of the gravity. The Saffman force is much less which only accounts for less than 10% of the gravity.2. Comparing the fluctuating wind field described by Langevin equation with the experimental data, it is verified that it is feasible to describe fluctuating wind field using Langevin equation. Then the trajectory characteristics of saltating particles in fluctuating wind field are studied. The results show that the fluctuating wind velocity has significant effect on the trajectories of saltating particles. When the particles' diameters are large, the trajectories of saltating particles take on smooth parabola; but as the particles' diameters decrease, the trajectories of saltating particles become irregular gradually. Using the saltation model of coupled interaction between sand movement and wind field, the mass flux in fluctuating wind field is also simulated. The results show that the mass flux obtained by theoretical calculation with consideration of the fluctuation of wind field agrees better with experimental data than without consideration of the fluctuation of wind field. Furthermore, the distribution of mass flux with height in fluctuating wind field shows obvious stratification feature, and the friction wind velocity and particles' diameters have significant effect on the mass flux.