动态风场及交通流量下街道峡谷内污染物扩散模拟

根据现场实测数据,应用标准k-ε模型研究了动态风场及交通流量下三维街道峡谷内的污染物扩散规律,数值模拟利用CFD软件FLUENT,其中动态风场和车流量变化信息通过用户自定义编程实现.结果发现,动态风场下空气在街道内部不断经历膨胀和压缩的过程,街道峡谷内部流场形态时刻都在变化;当风速由大变小时,空气膨胀出街谷,流型呈近似椭圆形分布;当风速由小变大时,空气压缩在街谷内部,流型呈近似圆形分布.风速的不断变化引起街谷内、外大气的压缩和膨胀过程,这种过程能够改善街谷内污染物的扩散情况.背风面行人高度处,动态来流下的平均污染物浓度要比定常来流下低17.7%;迎风面行人高度处,动态来流下的平均污染物浓度要比定常来流下低27.1%.动态环境下污染物浓度的分布和峰值由风场和车流量变化共同决定.

The numerical simulation of pollutant dispersion in street canyons under dynamic wind field and traffic flux conditions

Based on measured data,dispersion of pollutants in a street canyon under dynamic wind field and traffic flow were simulated by software FLUENT, with the standard k-ε model was adopted.The simulations showed that the fluctuation of inflow air velocities greatly changed the wind field in street canyons,resulting in the air mass expansion or contraction in the street canyon. The changing of wind field inside the street canyon could enhance the dispersion of pollutants. The averaged pollutant concentration at the pedestrian level near the leeward wall under the dynamic background wind condition was 17.7% lower than that under the steady background wind condition; and the averaged pollutant concentration at the pedestrian level near the windward wall under the dynamic background wind condition was 27.1% lower than that under the steady background wind condition. Pollutant dispersion and pollutant concentration peaks were affected by two factors,i.e., the background wind condition and the traffic fluxes.