Numerical Simulation On The Saltation Trajectories Of Sand Grain

The single sand law of motion is relates the wind-blown sand macroexamination and the microexamination link.Saltation is the most significant in the three basic forms (Saltation,Suspension and Creep) of sand movement blown by wind.In this paper,by comparing the common models in the numerical simulation of gas-solid flow, Lagrangian discrete particle model was chosen to achieve the real characteristics of the sand saltation.Sand saltation trajectories were calculated under the different inflow conditions such as logarithmic distribution,periodic sinusoidal and field gust of wind speed.The results showed that the consecutive saltation times of each saltation trajectories under former two wind conditions was less than that under gust condition.Next the influence of the turbulent intensity and the averaged wind speed on the saltation trajectories were discussed.It could be found that when the turbulent intensity and the averaged wind speed remained were fixed,the saltation trajectories of the sand with size less than the critical diameter were not smooth parabola unlike the trajectories of the sand with the size larger than the critical diameter.Therefore the influence of the turbulence on sand saltation needs to be considered in the numerical simulation when the sand size was less than critical diameter.When the turbulent intensity remained was definite value, the critical diameter of sand saltation sand increased with the averaged wind speed increased;when the averaged wind speed was fixed,the critical diameter increased with the turbulent intensity increased until the critical diameter grew up 200μm.The HL-model and the shape factor modification of sand were used in the numerical simulations of the sand saltation to study the effect of the sand's irregular shape on sand motion,and the simulation results were compared with measurement data of the high speed camera experiment.The results showed that the deviations were significant when the shape factor were not considered in the numerical simulations. The simulation results using HL-model were coincident with the experimental data in the vertical direction,and deviated obviously in the horizontal direction.For 200～300μm sand particles,the deviations of saltation height and saltation distance between the results of simulation using shape factor modification and experiment were 0.2%and 3.5%,and for 100～125μm sand particles,the deviations were 0.16%and 12.4%.