街道峡谷对称性对污染物扩散的影响

采用数值模拟的方法,研究了行列式和错列式街谷两侧建筑物的对称性对街谷内和下游建筑尾流区污染物浓度的影响,并引入3个用于评价室内空气环境的指标来描述街谷中人员区域内的空气质量.结果表明,平均残留时间(ART)和有效通风率(PFR)可用于评价不对称街谷内的空气质量.街谷的不对称性对街谷内部和下游建筑尾流区污染物浓度分布均有明显影响.下游建筑越低,则尾流区的浓度越高.行列式和错列式街谷中人员活动空间的无量纲平均浓度分别在建筑高度比例为7/3和7/2时最大.为在城市规划中尽可能避免出现最不利比例的街谷,根据平均残留时间和有效通风率等指标,给出了上下游建筑高度比与最不利街谷改善率的关系.

Effects of street geometric configurations on the pollutant dispersion around the canyons

The effect of street geometric configurations, i.e., building height layout, on pollutant distributions in both regular and staggered street canyons and the wake region of the downstream buildings are estimated by using the computational fluid dynamic (CFD) simulations. Three ventilation efficiency indices for evaluating indoor environment are applied to assess the air quality in the pedestrian domain. The numerical results show that average residence time (ART) and purging flow rate (PFR) can be used to evaluate the air quality inside the street canyons. The flow field and pollutant distribution inside and outside the canyon are greatly influenced by the building height layout, and the pollutant concentration in the wake region increases with decreasing the downstream building height. The highest values of the average concentration may occur in the pedestrian domain when the height ratios of the upstream building to the downstream building, i.e., H1/H2, are 7/3 and 7/2 for regular and staggered canyons, respectively. In order to avoid these unfavorable building height layouts during urban planning, the relationships between H1/H2 and the percentage reductions in PFR and ART are analyzed for both the regular and staggered arrangements.