Numerical Investigation Of Sand Saltation Over Slope Terrain

Wind-blown sand movement is a nonlinear stochastic systems with multi-scale and multi-field. Meanwhile, the complex terrain influences turbulent flow characteristics and sand transport near surface sand. Therefore, non-flat surface should be considered in the wind-blown sand model as an important factor. Since the randomness and intermittent of turbulent flow, it is difficult to measure the achieve real-time observations of turbulence flow and sand transport in the field environment. Although wind tunnel experiments is easy control, turbulent flow with high Reynolds number could not be achieved due to wind tunnel size restrictions. Currently, numerical simulation is an effective way to observe wind-blown sand field in real-time. Therefore, this paper carried out numerical simulation. Therefore, this paper simulates wind-blown sand characteristics over non-flat surface under the influence of turbulent. It is an important method to study wind-blown sand patterns in natural environment. And then, mechanism analysis of complex interactions among surface terrain, turbulence flow and sand particles is studied.Barchan as a typical dune shape has been the main research object in the study of sand dunes. Therefore, this paper selects the transverse section of Barchan as the basic terrain in order to discuss sand saltation over the barchan dune. This paper established coupled model of terrain, sand transport and turbulent flow. It provides theoretical prediction of wind-blown sand movement in natural environment. The main resaerch contents of this paper are discussed as folling aspects:In the second chapter, wind-blown sand movement over the slope surface was observed in the wind tunnel. Phase Doppler Particle Analyzer(PDPA) was used to measure wind flow velocity over the slope terrain in the wind tunnel. Furthermore, sand emission rate was measured at the different position by using Particle Image Velocimetry system(PIV) over the slope terrain. And also the sediment transport rate at different position over the slope terrain were measured by sand trap in order to verify the accuracy of the numerical simulation model. The experimental results show that sand emission rate and mass flux over windward slope surface are greater than over flat surface.In the third chapter, in considering the influence of terrain on wind-blown sand movement we establish a two-dimensional two-way coupling model of windblown sand movement over slope terrain. The SIMPLE(Semi-Implicit Method for Pressure-Linked Equations)algorithm was used to calculate the Navier-Stokes equation in order to simulate wind flow field. The sand transportation was calculated by tracking sand particle trajectory. The coupling effect of wind-sand was taking into account in the numerical simulation model. The slope terrain boundary condition was approached by using the immersed boundary method. Through the two-way coupling model we simulate and discuss wind velocity profile and sand transport rate at the different positions. The two-way coupling effect of wind-sand on the wind flow field over the slope morphology was analyzed. We also compared the numerical simulation results of sediment transport rate with wind tunnel experiment.Turbulence have great influence on sand saltation. The turbulence influence was considered in the model of wind blown sand movement over slope terrain. In the fourth chapter, large eddy simulation method was used to calculate the turbulent flow structure over flat surface. The same boundary condition of Fackrell and Robins(1982)wind tunnel experiment was used in the turbulence flow model in order to verify the model accuracy. Average wind velocity profile, turbulent kinetic energy and fluctuation velocity are analyzed.In the fifth chapter, three-dimensional turbulence model of windblown sand movement over slope morphology was established. We analyzed sand transport rate in the turbulence flow field at the different position over the slope morphology.In all, the study of sand saltation over slope terrain reveals the complex interactions among slope morphology, sand transport and turbulent wind flow. This paper gives the preliminary analysis method in the study of surface morphology and turbulent wind flow effect on sand saltation. It laid the foundation for depth research of sand transport over complex terrain in natural environment.