Effects Of Specularity Coefficient And Drag Force On Wind-Blown Sand Structure In Two-flow Model

From the view of the fluid mechanics, the wind-blown sand movement is a typical gas-solid two-phase flow, and its evolution depends on the interaction between the physical medium (air and sand) with different densities. With the rapid development of computer software, hardware technology and numerical calculation methods, computational fluid dynamics is widely used in the analysis and study of the dynamics characteristics of wind-blown sand flow. In order to be close to the actual situation of the wind-blown sand movement and to provide some analysis and numerical data for the experimental study, this paper used Euler-Euler two-fluid model in the FLUENT software, and simulated the development of the wind-blown sand flow under different conditions.First of all, using the Euler two-fluid model, we established the basic equations of the wind-blown sand, and a standard k-ε model was used in this paper to compute air phase turbulence movement. The basic governing equations of the sand movement were established with a supplement containing the additional of turbulent momentum transfer between gas and solid.Secondly, in the given computational domain and boundary conditions, we simulated the wind-blown sand movement in two-dimensional space, and three kinds of drag coefficient model (Syamlal-O’Brien, Wen-Yu and Gidaspow) and different thicknesses of the sand bed and specularity coefficients were taken into account in this paper. Then, we offered the distribution of solid particle volume fraction at chosen position and the time needed for wind-blown sand movement to reach the dynamic equilibrium. The computational results show that:the simulation using Syamlal-O’Brien drag coefficient model is much closer to the data of the field observations and experimental measurements; at the same position, while the specularity coefficient increases, the time for wind-blown sand flow reaching the dynamic equilibrium reduces, and the thickness of the saltation layer decreases; under the condition of same time and same section, along with the increase of the thickness of the sand bed, the sand volume fraction at the same height increases, and the time for reaching the dynamic equilibrium is longer.Finally, reasonable parameters were validated by comparing and analysing the computational results. The simulation results show that:the sand volume fraction in the wind-blown sand flow gradually decreases as time goes by until reaching the dynamic equilibrium. When the dynamic equilibrium reaches, the sand volume fraction along the height has the stratified rule of "increment-saturation attenuation". In the attenuation layer, the distribution of the sand volume basically shaped the form of negative exponential as the height increases. In the same position, the development of sand’s volume fraction along with the time presents an "increase-reduce-stable" trend. The numerical results are consistent with those in the literatures, therefore, it certifies that this model can better describe the wind-blow sand movement; to some extent, it provides a basis for the theoretical research and prevention of the desertification.