Numerical study on flow and dispersion in rban street canyons of asymmetrical configurations*

A study was carried out by using the numerical simulation method to obtain the total concentration of a specific objective street canyon for different layouts with the different aspect ratio of Hd/Hu (windward-building-height-to-leeward-building-height) under a specific street width. It is shown that the concentration distributions and the total concentration values are strongly dependent on the number and rotating direction of vortices within and out of the street canyon due to the variation of geometric configurations of the street canyon. The preliminary study for the limited street canyon configuration shows that there may exist a critical aspect height ratio to make the total concentration of the specific street canyon be small. Generally the strong step-down canyon is a good layout relative to the other types.