Influence of wind directions on the airflow and pollutant concentrations in the 3D street canyon with different canyon configurations

Abstract In the present study, effects of the wind directions on the airflow and pollutant concentrations in the different canyon configurations (step-up, flat and step-down canyon) are investigated by numerical simulation and the wind-tunnel experiment, respectively. Specifically, five wind directions of α = 90°, 60°, 45°, 30°and 0° (α is the angle between the approaching flow and street canyon) are considered in the step-up, flat and step-down canyons. The results reveal that the wind direction has a vital influence on the flow structures in the different canyon configurations. When α is relatively small (0°, 30°), ventilation capacity is similar in all of the canyon configurations (step-up, flat and step-down canyon). However, under the large α (45°, 60° and 90°) wind direction, the significant difference of ventilation capacity can be obtained among the step-up, flat and step-down canyons. When α = 45°, the ACH of step-up canyon is much higher than that of flat and step-down canyons. When α = 60° and 90°, ventilation capacity is the highest in the step-up canyon and the lowest in the step-down canyon. As for the pollutant concentrations on the building walls under the perpendicular wind direction, the leeward side of the step-up and flat canyons is polluted from the floor to the top and will affect the indoor air quality through the windows. For the step-down canyon, high pollutant occurred at the windward side, which is contrary to that in the flat and step-up canyon. Notably, the pollutant accumulated on the leeward side and then gradually change to concerned on the windward side of step-down canyon with the increases of α. The findings in the present study are conductive to understanding the effects of canyon configurations together with wind directions on the airflow structures and pollutant dispersion inside the canyon, and the results will provide technical support for urban building planning to control air pollution during the urban renewal.