屋顶形状对街道峡谷内污染物扩散的影响

采用Spalart-Allmaras湍流模型,通过求解二维连续性方程，Navier-Stokes方程及污染物输运方程，模拟了具有不同屋顶形状的街道峡谷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.由于屋顶形状的不同，峡谷内的流场会形成顺时针或逆时针方向的旋涡，从而影响建筑物迎风面与背风面污染物浓度分布.在各种屋顶形状的街道峡谷中，壁面污染物浓度的相对大小与其附近的速度分布有直接关系.通过对街道峡谷建筑屋顶高度处垂直方向污染物通量的计算和比较，说明了不同屋顶形状的街道峡谷平均流扩散和湍流扩散的强弱，污染物湍流扩散通量值有可能为正或为负；同时，峡谷内剩余污染物浓度的大小表明了屋顶形状对污染物扩散出街道峡谷难易的影响. 

Influence of Roof Shape on Pollutant Dispersion in Street Canyons

The influence of roof shape on the flow field and traffic pollutant concentration field in street canyons was investigated by two- dimensional numerical model, which was based on Reynolds-averaged Navier-Stokes equations, Spalart-Allmaras turbulence model and pollutant transport equations. A general agreement between the numerical and the wind tunnel experimental results was obtained. Because of different roof shapes, the flow regime in street canyons changed remarkably. The vortex orientation could be clockwise or counter-clockwise, resulting in quite different pollutant distributions on the leeward and windward walls. The concentration values on the walls were closely related with the nearby velocity magnitude. The vertical pollutant flux at the roof level of street canyons showed quantitative contributions of mean flow and turbulent flow to the pollutant escape from canyons. The vertical turbulent flux of pollutants could be upward or downward. Meanwhile the pollutant amount remained within canyons indicated the influence of roof shape on the pollutant dispersion extent from street canyons.