Numerical Investigation of the Effect of Green on the Convective Mass Transfer in the Street Canyon

The road green belt can affect the convective flow, heat and mass transfer in the street canyon. The CFD technology coupled with porous media model was applied to investigate the effects of the different road green arrangement patterns on the convective heat transfer and vehicle exhaust pollutant diffusion in the street canyon with W/H = 1 : 2. By analyzing the flow structure, temperature and pollutant distributions under different cases, it was found that the ventilation in the street canyon would be enhanced by the mixed flow (Ri=0.47) due to the heating ground, but not significantly. The roof greening can reduce the flowing air temperature and enhance the convection in the street canyon, but which also can cause the inflow velocity to get smaller and deteriorate the ventilation. In addition, the increasing green belts will reduce the ambient temperature in the street canyon significantly, but also obstruct the airflow more sharply. Furthermore, it reduced the average velocity in the street canyon to increase the high concentration area of pollutant CO.