风沙环境中公路风沙灾害的数值模拟

Numerical Simulation of Sand Transport around the Highway in Sandy Desert Area

为揭示沙漠公路两侧风沙流场的空间分布特性,采用欧拉-拉格朗日方法,把气流作为连续介质,把沙粒作为离散体系,利用ANSYS标准k-ε湍流模型和DPM离散相模型,模拟了不同沙粒粒径(150、200、250、300、350μm)、不同摩阻风速(0.20、0.35、0.50、0.65、0.80 m·s^(-1))、不同挡风墙高度(1.0、1.5、2.0、2.5、3.0 m)以及不同挡风墙开孔情况下的公路路基附近的沙粒跃移运动,统计了挡风墙前后的沙粒数目,给出了公路路基坡脚和坡顶等典型断面上的气流速度廓线。结果表明:气流通过挡风墙顶部时受压加速,有利于沙粒的输送,而在挡风墙前部气流遇阻减速,形成沙粒堆积。随着沙粒粒径的变大,沙粒跃过挡风墙的能力逐渐变低;随着摩阻风速的变大,气流输运能力增强,更多沙粒越过挡风墙;随着挡风墙高度的增加,阻挡沙粒数亦逐渐增多;挡风墙开孔的位置和大小亦影响着沙粒的运动。这表明离散相模型对复杂下垫面风沙跃移运动的计算具有良好的效果。

The objective of this study is to identify and describe wind-blown sand motion near and around the highway in sandy desert areas. The Euler-Lagrange approach was used to describe a coupled gas-solid two-phase flow. The air flow was treated as a continuous phase flow by solving the time-averaged Navier-Stokes equations,while the discrete sand particle motion was calculated based on the mean continuous flow field. We conducted a series of numerical simulations with different parameters by using ANSYS k-ε model and Discrete Particle Model. The sand particle diameters range from 150 μm,to 200 μm,250 μm,300 μm,350 μm,the friction velocity of air flow are from 0.20 m·s^-1,to 0.35 m·s^-1,0.50 m·s^-1,0.65 m·s^-1,0.80 m·s^-1,the height of retaining wall are from 1.0 m,to 1.5 m,2.0 m,2.5 m,to 3.0 m,and a variety of retaining walls with different openings are considered as well. The sand particles passing the retaining wall were counted statistically,the typical wind velocity profiles were depicted in this paper. The numerical results show that the flow speeds up at the top of the retaining wall,which is positive to transport of particles,while the flow slows down in the front of the retaining wall and between the wall and the roadbed,which leads to the sand deposition near these zones. As the sand particle becomes larger,the ability of sand particles over the retaining wall becomes lower;with the friction velocity being larger,block effect of windbreak of sand decreases;and with increasing of the retaining wall height,the sand amount over the wall will reduce;meanwhile,the opening position and size of the retaining wall play an important role on the sand movement near the highway. It is concluded that the discrete particle model is useful to the calculation of sand saltation in air,and can provide some theoretical support for the control of windblown sand and for the safe running and operation of highway in sandy desert areas.