Effect of moving vehicles on pollutant dispersion in street canyon by using dynamic mesh updating method

Abstract

Moving vehicles exert a considerable influence on air flow and turbulence within urban street canyons, which is an important consideration for the pollutant dispersion and thus, local air quality management. In order to evaluate vehicle-induced turbulence and its contribution to pollutant dispersion, this study proposes a computational fluid dynamics based simulation methodology that uses a dynamic mesh updating method. The unsteady RNG k-ε turbulence model was employed to investigate the turbulent kinetic energy (TKE) induced by vehicle movement and pollutant profile in the target street canyon. The simulation accuracy is successfully validated against a published wind tunnel experiment. The results demonstrate that: (1) The TKE is mainly located behind the vehicle, and the magnitude of the TKE around the moving vehicle body far exceeds that of stationary vehicles; (2) Travelling speed has a significant influence on the TKE. When the moving speed is 15 m/s, its TKE near the tail is about 1.8 times and 6.3 times than that at 10 m/s and at 5 m/s, respectively; (3) Vehicle movement greatly contributes to pollutant dispersion. Compared to no vehicle movement (V = 0 m/s), vehicle-induced turbulence with V above 5 m/s can reduce the carbon monoxide concentration by about 4% at breathing height.