A Laboratory Model for the Flow in Urban Street Canyons Induced by Bottom Heating?

Water tank experiments are carried out to investigate the convection flow induced by bottom heatingand the effects of the ambient wind on the flow in non-symmetrical urban street canyons based on thePIV (Particle Image Visualization) technique. Fluid experiments show that with calm ambient wind,the flows in the street canyon are completely driven by thermal force, and the convection can reach theupper atmosphere of the street canyon. Horizontal and vertical motions also appear above the roofs ofthe buildings. These are the conditions which favor the exchange of momentum and air mass between thestreet canyon and its environment. More than two vortices are induced by the convection, and the complexcirculation pattern will vary with time in a wider street canyon. However, in a narrow street canyon, justone vortex appears. With a light ambient wind, the bottom heating and the associated convection resultin just one main vortex. As the ambient wind speed increases, the vortex becomes more organized and itscenter shifts closer to the leeward building.