Kinematics and dispersion characteristics of flows in asymmetric street canyons

Abstract

Flow visualization and tracer concentration measurements were made in street canyon models in which the ratio of street width to the height of the upwind building was held constant at 0.79 while the ratio of the heights of the upwind and downwind buildings was varied between 2.0, 1.0 and 0.67. Tracer measurements were obtained across the face both of the leeward and windward buildings from independent emissions on the canyon floor and the roof of the upwind building. Orientation of the canyon axis with respect to the free stream flow was varied from 0 to ± 90 deg in 10 deg increments. The structure of the dispersion patterns is strongly dependent on the canyon asymmetry and less dependent on the canyon orientation to the prevailing flow. Comparisons are presented among vertical concentration-profiles observed on the two canyon faces and estimates from one analytical and one empirical model. Bubble tracers were used to study circulation patterns: for the even notch configuration, the circumferential velocity is observed to be about one-fourth of the free stream velocity, while the ratio of velocities is about one-half for the step-up notch configuration.