Numerical Simulation on the Effect of Vehicle Movement on Pollutant Dispersion in Urban Street

Combined processes of ambient crosswind and vehicle-induced turbulence have a very significant effect on the distribution of pollutants emitted by vehicles in street canyon. So the purpose of this study is to analyze the process of pollutants dispersion when moving vehicles pass the urban streets based on the basic theory of hydromechanics. The air flow and pollutants dispersion in a street canyon in the presence of a moving vehicle by a dynamic mesh approach using computational fluid dynamics (CFD) is investigated. The standard k-epsilon model and enhanced wall functions are employed to establish airflow field, and species transport model and the tracer gas technique are combined to simulate pollutants dispersion. The simulation results are compared with the published experimental data of mean velocity and turbulence for the validation. Then on the base of this validation, we further explore the effect of vehicle speed and the vehicle driving lanes. This study is a good understanding of the mechanism of vehicle-induced pollutants dispersion within the urban street canyon. Thanks to the different piston effect formed by moving vehicle in different lanes, the concentration on the leeward side in the descending order are L1, No vehicle, L4, L3, L2. Meanwhile, the concentration of pollutant behind the vehicle on the leeward side decreases with increasing vehicle moving speed. Higher moving speed could lead to a reduction of concentration on the windward side.