A laboratory model of urban street-canyon flows

A circulating water channel is constructed to examine urban street-canyon f low. In the cases of an even-notch street canyon in which model buildings o n both sides of the street have equal heights, one vortex is observed in mo del canyons with aspect ratios of 1 and 1.5, and two counterrotating vortic es are observed in canyons with aspect ratios of 2, 2.4, and 3. In all of t he even-notch cases, the center of the vortex (or the upper vortex) is loca ted slightly downstream of the canyon center, and the downward motion downs tream is stronger than the upward motion upstream. The magnitudes of the ma ximum updraft and downdraft are almost independent of the aspect ratio. In the case of a stepup notch, one vortex is observed in the canyon. In the ca se of a stepdown notch, two counterrotating vortices are observed. The uppe r 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 o f the water-channel experiments are generally in good agreement with those simulated using a numerical model with a turbulent kinetic energy-dissipati on (k-epsilon) turbulence closure scheme, although there is a noticeable di fference in the relative strengths of the upper and lower vortices in the t wo-vortex regime. This study demonstrates that the circulating water channe l is useful for the study of street-canyon how.