CFD simulation of pollutant dispersion in a street canyon: Impact of idealized and realistic sources

Pollutant dispersion is of great relevance for people living in urban areas. High levels of pollutant can usually result from the combination of poor natural ventilation and high-traffic volumes of vehicles. Idealized point and line sources are commonly used to reproduce traffic emissions in simplified portions of urban areas, as street canyons. However, a limited number of studies focuses on the usage of realistic sources, as real car geometries which can influence the flow characteristics and the pollutant distribution inside the canyon. This is also the goal of the present paper for which Computational Fluid Dynamics (CFD) simulations were performed by means of scale-adaptive simulation (SAS) on a street canyon to investigate the impact of idealized and realistic sources. In stage 1, SAS simulations were performed with idealized line sources by reproducing reduced-scale wind-tunnel (WT) experiments. In stage 2, SAS simulations were carried out on a street canyon using idealized line sources and realistic sources with different levels of simplification. The results showed that the use of realistic sources can result in an increased concentration of 1.03 - 6.76 (at z = 0.33 m above the ground), with respect to the use of idealized line sources. Overall, at the lower level of the street canyon (e.g. z < 1.5 m), the concentration can be strongly affected by the presence of the car bodies. The results of the present study are expected to help urban planners as well as governmental institutions to reduce pollutant concentrations in the street canyon.