优选数值计算方法用于不对称街道峡谷的研究

分别将迎风、混合及调和QUICK格式用于对称街道峡谷的汽车排放污染物浓度预测，并与风洞实验结果相比较，研究表明数值模拟与风洞实验吻合较好，调和QUICK格式的预测效果最佳。将调和QUICK格式用于不对称街道峡谷的研究，发现当迎风面建筑物高于背风面建筑物时，峡谷内的流场和浓度场与对称街道峡谷相似，即峡谷内有一个顺时针方向的强漩涡，使得背风面污染物浓度高于迎风面污染物浓度。同时，随着迎风面建筑物高度的增加，漩涡中心的位置成垂直向上分布，且与迎风面建筑物的高度基本成线性关系；当迎风面建筑物低于背风面建筑物且差别较大时，街道峡谷内出现了两个反时针方向旋转的强漩涡，使得峡谷内的流场与浓度场都发生较大的变化，迎风面污染物浓度会高于背风面污染物浓度。同时表明，峡谷上方的顺时针方向漩涡的中心呈抛物线向右上方向发展，而峡谷下方的逆时针方向旋涡的中心呈抛物线向左E方向发展。

Study of a symmetrical street canyons with the optimized difference scheme

The Upwind,Hybrid and HQUICK schemes were firstly used to predict the vehicle exhausted pollutant dispersion in a symmetrical street canyon. The HQUICK scheme was proved to be the best by comparing the predicted results with that of the wind tunnel experiment. By use of the HQUICK scheme to study the asymmetrical street canyons, it was found that when the windward side of building in the canyon is higher than the leeward side of building, the flow field and concentration field are similar to those in the symmetrical street canyon,that is, a strong clockwise vortex exists in the street canyon and there are much more pollutants on the leeward side than on the windward side and the concentration of pollutants increases with the decrease of the height of the building. And with the increase of windward building, the vortex center increases vertically and linearly with the building height of windward side. When the windward side of building is lower than the leeward side, there are two vortices with reversal rotation direction in the street canyon if the ratio of the height of leeward side of the building to the windward side is smaller than a critical value. So the flow field and concentration field are quite different from that in the symmetrical street canyon, and the concentration of pollutants on the leeward side may be higher than that on the windward side of the buildings. It was also found that the vortex center of the upper vortex with clockwise rotation develops towards the upper right direction in a parabolic path, while the vortex center of the lower vortex with counterclockwise rotation develops towards the upper left direction in a parabolic path.