A Numerical Study of Thermal Effects on Flow and Pollutant Dispersion in Urban Street Canyons

Abstract This study investigates thermal effects on the flow and pollutant dispersion in urban street canyons. A two-dimensional numerical model with a k–ϵ turbulent closure scheme is developed, and the heat transfer between the air and the building wall or street-canyon bottom is effectively represented by a wall function. For each of seven cases with different aspect ratios (building height/width between buildings = 0.5, 1, 1.5, 2, 2.5, 3, and 3.5), four thermal situations (no heating, upwind building-wall heating, street-canyon bottom heating, and downwind building-wall heating) are considered. In the cases of upwind building-wall heating, one vortex appears regardless of aspect ratio. When the aspect ratio is greater than or equal to 1.5, the upward motion forced by upwind building-wall heating overcomes the downward motion that appears in the cases of no heating. In the cases of street-canyon bottom heating, when the aspect ratio is less than 3, flow patterns are similar to those in the cases of upwi...

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