CFD Study on the Effects of Trees on Pollutant Dispersion in a Street Canyon

The objective of this study is to investigate the effects of trees on flow and pollutant dispersion in a street canyon. For this, the drag effect of trees are considered in the CFD model. Simulated results are validated against the wind-tunnel results. For comparison, the same building configuration as the wind-tunnel experiment are considered. To investigate the effects of trees, flow and pollutant dispersion fields in the low-density tree and medium-density tree cases with the pressure loss coefficients of 80 and 200 Pa m-1, respectively were compared to those in the tree-free case. As the tree density increased, wind speeds overall decreased in the street canyon and pollutant concentrations increased near the upwind building wall and decreased near the downwind building wall. This resulted from the drag effect of trees located at the center of street canyon. The flow and concentration distribution simulated by the CFD model were quite similar in pattern to those in the wind-tunnel experiment. The simulated results were further evaluated using several statistical methods. It was concluded that the CFD model with the drag effect of trees successfully simulated the measured flow and pollutant dispersion in the wind-tunnel experiment.