A Numerical Study on Sensitivity of Pollutant Dispersion to Turbulent Schmidt Number and Inflow Wind Speed in a Street Canyon

Sensitivity of turbulent Schmidt number and inflow wind speed to pollutant dispersion in an urban street canyon is investigated in this study. First, we compared the CFD‒simulated results to wind‒tunnel results. For this, we changed systematically inflow wind speed at the street‒canyon height (1.5 ~ 10.0 m s-1 with the increment of 0.5 m s-1) and turbulent Schmidt number (0.2 ~ 1.3 with interval of 0.1). Also, we performed numerical experiments under the conditions that turbulent Schmidt numbers selected with the magnitude of mean kinetic energy at each grid point were assigned in the street canyon. With the increase of the inflow wind speed, the model underestimated (overestimated) pollutant concentration in the upwind (downwind) side of the street canyon because of the increase of pollutant advection. This implies that, for more realistic reproduction of pollutant dispersion in urban street canyons, large (small) turbulent Schmidt number should be assigned for week (strong) inflow condition. In the cases of selectively assigned turbulent Schmidt number, mean bias remarkably decreased (maximum 60%) compared to the cases of constant turbulent Schmidt number assigned. At week (strong) inflow wind speed, root mean square error decreases as the area where turbulent Schmidt number is selectively assigned becomes large (small).