Large-eddy simulation of turbulent flows and pollutant transport inside and above idealized urban street canyons under different unstable thermal stratification

摘要

Large-eddy simulation (LES) is employed to study the behaviours of flows and pollutant transportinside and over idealized urban street canyons under different unstable thermal stratification. Threeconfigurations of idealized street canyon, consisting of building-height-to-street-width (aspect) ratios,0.5, 1 and 2, are considered. Under unstable stratification, the vertical profiles of streamwise velocityand temperature over the bottom rough surface are more uniform and the turbulent transport ofmomentum and heat are enhanced. Inside the street canyons, the ventilation performance, which arecharacterized by the air exchange rate (ACH), pollutant exchange rate (PCH), pollutant retention timeand average pollutant concentration, is found improved in unstable stratification.