Impact of viaduct on flow reversion and pollutant dispersion in 2D urban street canyon with different roof shapes - Numerical simulation and wind tunnel experiment

Abstract A numerical simulation and a wind tunnel experiment are performed to investigate the flow field and pollutant dispersion in a two dimensional (2-D) ideal urban street canyon with roofs installed in a viaduct at different heights. Two typical roof shapes are taken into consideration: double flat (DF) and double triangular (DT). The simulation results show that when the height of the viaduct is at 0.875 H –0.98 H for DF and at 0.71 H –0.988 H for DT, the main flow field in the canyon will be reversed compared to initial flow field. This reversing phenomenon will aggravate pollution for DF and significantly mitigate pollution for DT compared to levels without a viaduct. The wind tunnel experiment is qualitatively consistent with the numerical simulation results which indicates that this reversing phenomenon is not just theoretical. A mechanism is proposed whereby the viaduct obstructing airflow is the key reason for the flow field reversion.