Impacts Of Upstream Buildings On The Flow Fields And Pollutant Distributions In Street Canyons

Local air environment in building clusters not only has directly effects on the health of theresidents who live in the district and pedestrians, but also has significant impacts on urban airenvironment. With the rapid increase of the city’s vehicle fleet, the pollutant emission fromvehicles has become one of the main factors affecting the urban air environment. Because of thebuilding layouts in urban areas have direct effects on the atmospheric dispersion of pollutants, it isimportant to study the airflow fields and pollutant distributions in street canyons for predictingchanges in urban air environment and providing some available information for urban planning.Based on the previous studies, numerical simulations have been conducted for exploring theenvironment of street canyons with different building layouts by employing CFD techniques.Under the same background wind speed, and according to the numerical simulations, the airflowvelocity and the diffusion of pollutants were analyzed for different positions, different directions,and different height. Moreover, same analyses and discussions were made under differentbackground wind speeds.The numerical results showed that the upstream buildings change the local wind speed anddistort the secondary flows in the canyons and thus have significant effects on the flow andconcentration fields. In the regular street canyons, the average pollutant concentrations could bereduced regardless of layout of the upstream buildings. The average concentration would beoverestimated by numerical simulations without considering the existence of the upstreambuildings in practice. Inside the staggered street canyons, when upstream buildings are alignedwith street canyons, the pollutant concentrations in the street canyon could be reduced by theblocking effect. In contrast, when the upstream buildings are staggered with the canyons, theconcentrations could be increased. The results also showed that the pollutant dispersion andremoval in street canyons are effected by both the airflow velocity and local vortex characteristics.In addition, for regular street canyon, when the background wind speed increases, the features ofthe airflow velocity and pollutant concentration distribution will not be changed, only the values of the speed and concentration can be changed. For the staggered canyon, both the airflow patternand the concentration field will be changed.