Thermal Effect on Pollutant Dispersion in an Urban Street Canyon

Abstract

his investigation was carried out to reveal the impact of solar radiation on wind flow structure and pollutant dispersion in an urban street canyon of aspect ratio of one using the computational fluid dynamic (CFD) technique. The simulation results (velocity and concentration data) show that heating from building wall surfaces and ground lead to strong buoyancy forces as the air is heated by the wall surface when receiving direct solar radiation. This thermally induced buoyancy plays a significant role in determining flow fields within street canyon. When the sun shines on the leeward side of the building and the ground, the airflow structure and pollutant dispersion patterns are similar to that without solar radiation, the buoyancy flux adds to the upward advection flux along the wall strengthening the original vortex. When the windward wall is warmer than the air, an upward buoyancy flux opposes the downward advection flux along the wall, and divides the flow structure into two counter-rotating vortices indicating a clockwise top vortex and a reverse lower vortex within the canyon. Further, the impact of various temperature differences on the windward heating and different velocities for inlet velocity has been examined. The relative influence of the thermal effect can be estimated by bulk Richardson number (Rb).