风向对街道峡谷内污染物扩散的影响

采用Fluent软件，选用RNG k-ε湍流模型，对长高比为5的街道峡谷(简称街谷)在0°～90°风向下流场和污染物浓度场进行了数值模拟. 结果表明: 0°～75°风向时，街谷内流场呈明显的三维特性，90°风向时，流动表现出中长街谷的二维特点；风向对街谷内壁面污染物浓度的分布有显著影响，90°风向下的街谷壁面浓度最大，其次是45°风向，其余风向下的相对较小，污染物浓度的计算值与风洞试验值在趋势上吻合较好；壁面污染物浓度的分布由街谷内长度方向漩涡、来流冲角产生的进口回流及沿长度方向的流动所决定，壁面浓度的分布差异均可从附近的流场获得解释. 街道峡谷内长度方向的漩涡模拟过强会导致地面附近污染物浓度的计算值偏离试验值. 

Influence of Wind Direction on Pollutant Dispersion in a Street Canyon

The influence of wind directions from 0° to 90° on flow and concentration fields in a street canyon with length to height ratio of five was numerically simulated using the RNG k-ε turbulence model.The governing equations were solved using Fluent software.The results showed that three-dimensional flow features were depicted for wind directions of 0° to 75°,while two-dimensional flow features were shown for the wind direction of 90°.The distribution of wall concentrations in the street canyon was significantly affected by wind direction.The maximum wall concentration occurred at the wind direction of 90°,and the second highest value occurred at the wind direction of 45°.The wall concentrations were relatively smaller at other wind directions.The predicted concentrations were validated against wind tunnel data,and good agreement was obtained.The wall concentrations were determined by the in-canyon vortex,the backflow caused by the incident wind angle and the horizontal flow along the canyon length.The difference of wall concentration distribution at different wind directions could be illustrated from the flow fields near the wall.The over-predicted canyon vortex may lead to discrepancies between the computed concentrations and experimental results.