Large-eddy simulation of pollution dispersion in an urban street canyon—Part II: idealised canyon simulation

Abstract

Three-dimensional large-eddy simulations are performed with the dynamic sub-grid scale model for an idealised urban canyon with pollution modelled as a passive scalar. In addition to concentration distributions, turbulence statistics for the canyon are presented. Higher turbulence intensities are predicted in the core of the vortex compared to the widely used k– ε model. This results in a more homogeneous distribution of pollutants, in agreement with experimental studies reported in the literature. Regions of enhanced turbulence are also observed near the walls leading to a lateral dispersion of pollutants along the canyon. The centre of the vortex is observed to precess around the canyon and also meanders along the length of the canyon. Puffs of pollution are ejected from the top of canyons intermittently rather than smoothly, with a characteristic time scale of the order of 30–60 s.