Large-eddy simulation of reactive pollutant dispersion in a street canyon using a subgrid scale variance model of concentration field

ABSTRACT: Bi-molecular reactions can affect the transport of air pollutants in urban street canyons. In numerical simulations, we need to evaluate the correlation between the concentrations of the reactants to know the reaction rate. In this paper, we examine the effects of the subgrid scale (SGS) on the reaction rate in large-eddy simulations (LESs). LESs coupled with an SGS variance model are used to study the dispersion of both inert and reactive pollutants in a simulated street canyon. First, we conduct simulations of an inert pollutant at different grid resolutions. The results of these simulations demonstrate the validity of our model for calculating the variance of concentration at the SGS. Second, we apply the model to the dispersion of reactive pollutants. The correlations of the SGS variances become relatively large in a free shear layer at the height of the canyon. However, the SGS variance is very small and has a negligible impact on the mean concentrations of pollutants within the canyon.