Large Eddy Simulation of the aerodynamic role of trees on airflow and pollutant dispersion in urban street canyons

This work analyses the aerodynamic effects of avenue-like tree planting on the flow field and dispersion of pollutants in urban street canyons by means of large eddy simulations (LES) coupled with the Dynamics Smagorinsky-Lilly Subgrid scale model and the advection-diffusion module for concentration prediction using the commercial CFD software FLUENT. Flow and concentration levels are compared between an empty (i.e. tree-free) street canyon and one containing avenue-like tree planting with two porosities of λ = 80 m-1 and λ = 200 m-1. In the presence of trees, considerably larger pollutant concentrations near the leeward wall and slightly lower concentrations near the windward wall are observed in comparison to the tree-free case. The difference in porosities did not play a significant role. Simulation results obtained by LES are agreeable to wind tunnel (WT) measurements due to the resolution of the internally induced fluctuations.