大气边界层中沙粒悬移运动的数值模拟

Numerical Simulation of Sand Suspension and Transportation in Atmospheric Boundary Layer

将双时间法和k-ε湍流闭合模型应用于求解雷诺平均的Navier-Stokes方程,模拟了沙地、沙丘流场。在此基础上,应用梯度输送理论求解平流扩散方程,模拟了平坦沙地、单个沙丘和连续沙丘周围沙粒的悬移。结果表明:1)来流的风速度足够大,使得地面摩擦速度大于起沙的临界速度,这是沙粒发生悬移的必要条件。但是光有足够的风速还是不够的,要使卷入空中的沙粒能在较大的高度范围内扩散,流场中必须存在一定强度的抬升气流。比较剧烈的地形起伏容易造成流动的不稳定;2)只有流场中存在抬升气流,才会使沙粒扩散到较高的高度;3)平坦地形时气流偏折主要是压力梯度的作用;而在沙丘起伏的表面,气流偏折受沙丘地形的影响很大。

A dual-time method and k-ε turbulent closure scheme are used to solve Reynolds averaged Navier- Stokes equations. The flow over dunes is simulated. And then the transportation-dispersion equation is solved with K theory to simulate the suspension and transportation of sands. The results show that, 1） the necessary condition of sand suspending is that the wind speed of inflow is so large that the surface friction velocity is larger than the threshold velocity for rising sand. If only there is certainly strong lifting air stream, the involved sands can spread highly. 2） The lifting stream can be caused by the unstable flow or the obvious change of terrain. 3） The main factor that cause the stream deflect over flat terrain is pressure gradient, however over dunes the terrain have important impact on the stream