孤立与非孤立城市街道峡谷内污染物扩散

通过求解二维不可压N-S方程、k-ε方程及污染物对流扩散方程,模拟了孤立街道峡谷与非孤立街道峡谷内的流场及交通污染物浓度场.计算结果与风洞试验结果总体趋势一致.非孤立街道峡谷内污染物壁面浓度要大于孤立街道峡谷内的壁面浓度.通过计算街道峡谷建筑屋顶高度处的垂直方向污染物通量,说明了湍流扩散是污染物扩散出街道峡谷的主要原因,其污染物通量总为正,而平均流通量可以为负.非孤立街道峡谷由于平均流流动和湍流流动的总扩散通量减少,造成污染物在街道峡谷内集聚,从而理论上解释了非孤立街道峡谷与孤立街道峡谷污染扩散的差别.

Pollutant dispersion in urban isolated and non-isolated street canyons

The flow field and traffic pollutant dispersion of urban isolated and non-isolated street canyons were investigated by two-dimensional numerical model,which was based on Reynolds-averaged N--S equations,k--e turbulence model and pollutant transport equations. A general agreement between the numerical and experimental results was obtained. The pollutant concentration was greater in non-isolated street canyons than in isolated street canyons. The vertical pollutant flux at the roof level of the street canyons showed that the turbulent flux was the main reason for the pollutant escape from canyons. The vertical turbulent flux of pollutants was upward everywhere, while the vertical flux by mean flow was upward or downward. Compared with isolated street canyons, the decreasing in total flux within non-isolated street canyons resulted in the pollutant buildup, which gave the theoretical explanation for the test results.