A Laboratory Model of Urban Street-Canyon Flows

Abstract

A circulating water channel is constructed to examine urban street-canyon flow. In the cases of an even-notch street canyon in which model buildings on both sides of the street have equal heights, one vortex is observed in model canyons with aspect ratios of 1 and 1.5, and two counterrotating 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 the 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 are almost independent of the aspect ratio. In the case of a stepup notch, one vortex is observed in the canyon. In the case of a stepdown notch, two counterrotating 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 a numerical model with a turbulent kinetic energy–dissipation (k–ε) turbulence closure scheme, although there is a noticeable difference in the relative strengths of the upper and lower vortices in the two-vortex regime. This study demonstrates that the circulating water channel is useful for the study of street-canyon flow.