Numerical Simulations Of Wind-blown Sand Saltation With Consideration Of Two Feedback Mechanisms

For the sand saltation is a stochastic and complex process, the exiting model rarely consider the effects of mid-air collision between sand particles on wind-sand flow. In this dissertation, a theoretical model is suggested to mathematically describe the wind-sand flow by considering the mid-air collision mechanism as well as the existing wind-particle feedback mechanism, and quantitatively simulate the influence of mid-air collision mechanism on structure of the wind-sand flow. The main works are concluded as follows:1. Based on the exiting mid-air collision probability model and the theoretical modeling of the wind blown sand movement at the steady state with concerning the coupled interaction between saltation particles and wind, a model is established with consideration of the mid-air collision mechanism and the wind-particle feedback mechanism to simulate the sand mass flux at heights and sand particle' trajectory.2. On the base of the theoretical model above and the probability distribution function which considers both horizontal and vertical velocity, the mass flux against heights and sand transport rate against wind friction velocity are discussed under three conditions which are only considering the probability distribution function of vertical velocity, considering the probability distribution function of horizontal and vertical velocity, and both considering the probability distribution function of horizontal and vertical velocity and the mid-air collision mechanism. It suggests that the results, with consideration of the probability distribution function of horizontal and vertical velocity and the mid-air collision mechanism, are less and much closer to the corresponding values of experiments when the sand diameter is large than 0.5mm. While for the sand diameter less than 0.5mm, it might consider other factor, such as irregular shape of sand particle.3. Then the shape of sand particle is taken into account in the theoretical model. Choose six non-spherical sand particles to analysis the influence of different particle shape on the structure of wind-sand flow. The simulation results show that the shape of particles has great influence on the mass flux; at the same situation, the difference of mass flux of different shape particle may be up to several times; for same shape, the mass flux is increasing with the aspect ratio; for the elliptical particle and cylindrical particle,, when the aspect ratio is larger than one, their mass flux is larger then the spherical particle's, while the aspect ratio is less than one, their mass flux is less then the spherical particle's. So the shape of sand particles is also an important factor of mass flux.4. A theoretical model is developed to mathematically describe the evolution of wind-sand flow by considering both the exiting wind-sand feedback mechanism and the particle mid-air collision mechanism, based on the theoretical model of wind-sand flow evolution which only considers the interaction between wind and sand, the sand-bed collision. Then the entire process of sand saltation is simulated quantitatively. The simulated results show that the particle mid-air collision mechanism makes a great contribution to the whole evolution process and the sand transport.