Advances in the fine scale simulation of urban wind environment

This work gives a review of studies on the air flow and pollutant dispersion in the fine scale environment of the urban street canyon. The affecting factors on the air flow and pollutant dispersions in urban street canyons are illustrated by analyzing the street canyon physical model and boundary conditions. The building layouts along the street and the variations in the ambient wind velocities and directions could contribute an impact on the basic air flow within urban street canyons, while the atmospheric instabilities inside the street canyons, the vehicle induced turbulence, and tree plantings could affect the turbulence and pollutant distributions inside the street canyons, especially under weak-wind conditions. In the case of the street canyons with high aspect ratio (building height H over street width W), Reynolds number would be related to the vortex structure. The current empirical or semi-empirical models are lacking of careful description of the street canyon's real geometries and atmospheric conditions, which had often resulted in large errors in the simulated or forecasted results. Based on the computational fluid dynamic (CFD) method, further development of numerical models should focus on the integrated model, taking account of canyon's real geometries and the real atmospheric conditions.