Convective dispersion of heat and airborne pollutants inside street canyons under the influence of urban ground heat flows

This paper reports a computational fluid dynamics simulation of airflow and species dispersion inside street canyons and building blocks simultaneously. Urban thermal boundary flows could cause a profound effect on the dispersion of pollutant scalars and ventilation performance of street canyons. Nominal pollutant concentration differences between the urban street canyon and the countryside fresh air could be determined by a consideration of wind profile and ground vegetation. This study models the interaction of the fluid flow, thermal and pollutant dispersions based on the Reynolds number (Re), Grashof number (Gr) and their combinations - Archimedes number (Ar). The fluid, heat and pollutant dispersion performances were compared with the air, heat and pollutant removal efficiencies, indicated by the air change rate (ACR), heat removal rate (HRR) and pollutant removal rate (PRR). Numerical results indicate that Ar could promote fluid, heat and pollutant removals in street canyons. Transport function lines (contours of heat and mass functions) produced would illustrate the main recirculation developed inside these street canyons studied, to allow development of control strategies for dispersion of heat and pollutant species within these environments. The present work could contribute towards the understanding of the ventilation mechanism in street canyons surrounded by the residential buildings.