Numerical evaluation of turbulence induced by wind and traffic, and its impact on pollutant dispersion in street canyons

Abstract

In cities, street canyons are common features that affect the exposure level and health of pedestrians, drivers, and passengers. The purpose of this study is to analyze the characteristics of velocity, turbulence, pollutant dispersion, and pedestrian exposure levels inside a nearly 400 m asymmetrical street canyon in Dalian, China. We present a realizable k–ε turbulence model, with additional vehicle-induced turbulence (VIT) source terms in the momentum equation, turbulent kinetic equation, and turbulence dissipation rate equation, to simulate velocity and pollution diffusion under the predominant wind directions, varying inlet wind flow conditions, and different vehicle speeds. The results showed that the VIT effect dominated the velocity and pollution distribution under continuous traffic flow conditions. A significant underestimation of up to 33% for velocity, and obvious overestimation of up to 78% for CO concentration, appeared if the effect of VIT was neglected. The results also indicated that more attention should be paid to pedestrian health, as extremely high exposure levels occurred during traffic rush hours due to high vehicle exhaust emissions.