Impacts of wind direction on the ventilation and pollutant dispersion of 3D street canyon with balconies

Abstract

Road side shapes, including balconies, have great impacts on airflow around buildings, but the couple-effect of the balcony structure and wind direction on the canyon ventilation has not been fully studied. Considering five wind directions (α = 0°, 30°, 45°, 60°, and 90°) and three discontinuous balcony arrangements (leeward-side balcony, windward-side balcony, and both-sides balconies), this study aims to investigate the effect of wind directions on the ventilation of the canyon with balconies via computational fluid dynamics (CFD). The turbulence modelling method is validated by reported wind-tunnel experiment in the literature. Moreover, ACH (air exchange rate) and NEV (net escape velocity) were used to evaluate the ventilation capability of the canyon. The results demonstrates that under all the wind directions, the ventilation capacity of the canyon with the balconies is lower than that of the regular canyon. Also, at most wind directions (α = 0°, 30°, 45°, and 60°) except α = 90°, the ventilation of the canyon with leeward-side balcony is the best, and that is the worst in the canyon with both-sides balconies. In addition, for all the canyon with balconies, with the increase of α, the ventilation capacity of the leeward pedestrian domain (leeward NEV*) becomes lower. From the result of this study, it is recommended that when designing buildings with balconies, balconies should be arranged in the buildings on the leeward side as far as possible. This paper will be useful for urban planners to design cities with high self-ventilation capacity.