风沙流中近床面沙粒三维运动的LES-DEM分析

LES-DEM study of 3-D motion of sand particles nearing bed in aeolian sand transport

采用自行开发的大涡模拟(Large-Eddy Simulation,LES)和离散单元法(Discrete Element Method,DEM)耦合的数值计算程序,对风沙气固两相三维运动进行了数值模拟。对近床面沙粒的起跳速度、起跳角、入射速度和入射角的概率分布,以及沙粒展向速度的分布做出统计分析。结果显示:本文所建立两相耦合数值模型,能够复现风沙输移中散体沙粒的运动特征;入射速度和起跳速度服从对数正态分布,并随着来流平均风速增大,概率分布呈现集中趋势;入射角、起跳角分别集中在10°和15°左右,表明沙粒动能向垂直方向转移的趋势;沙粒的展向速度的随来流风速增大而更加显著。

The numerical code base on coupling of large-eddy simulation （LES） and discrete element method （DEM） is developed. Three dimensional transport of gas-solid two phase aeolian sand is simulated with the code. Velocities and angles of incident and lift-off sand particles near the surface of sand bed are analyzed statistically. The re suits show that the code is able to simulate the features of motion of sand particles in aeolian sand flow. The lognormal function can be used to express the distribution of incident and lift-off velocities of sand particle. The value of distribution functions in a more focused with the increase of wind speed. Angle of incident and lift - off concentrate in 10 and 15 degree separately. This indicate that the momentum of sand particles tend to transfer to the vertical direction. Spanwise velocities of sand are more significant with the increase of wind speed.