An Experimental Investigation of Urban Street-Canyon Flows

A circulating water channel is constructed to examine urban street-canyon flow. In cases of even-notch, one vortex is observed in model canyons with aspect ratios of 1 and 1.5 and two counter-rotating vortices are observed in canyons with aspect ratios of 2, 2.4, and 3. In all of the even-notch cases, the center of the vortex (or upper vortex) is located slightly downstream of the canyon center and the downward motion downstream is stronger than the upward motion upstream. The magnitudes of the maximum updraft and downdraft upstream and downstream, respectively, are almost independent of the aspect ratio. In a case of step-up notch, one vortex is observed in canyon. In a case of step-down notch, two counter-rotating vortices are observed. The upper vortex resembles to some extent an isolated roughness flow and the lower vortex is characterized by a skimming flow. It is shown that the results of the water channel experiments are generally in good agreement with those simulated using the numerical model with a k-¥åturbulent closure scheme, although there is a noticeable diffenence in the relative strength between the upper and lower vortices in the two-vortex regime. This study clearly demonstrates that the circulating water channel is useful for the study of street-canyon flow.