Comparison of wind-tunnel and full-scale street-canyon data from Joint Urban 2003

Abstract – The complexity of the flow structure in urban street canyons is well known from previous studies. However, a number of previous studies, particularly in the wind-tunnel, focused on the flow in street canyons with idealized, regular building geometries. For such building arrangements, a characteristic flow feature is often a 2D-like vortex rotating, which has been frequently observed in narrow streets under perpendicular approach flow. The formation of typical street-canyon vortices becomes however questionable in complex urban settings with highly variable building geometries and fluctuating meteorological conditions. New insights on the nature of urban flow and dispersion patterns can be expected from the data collected during the Joint Urban 2003 street-canyon sub-experiment for which more than 40 3D-sonics were continuously operated inside a relatively narrow downtown street (Park Ave.). The field data analysis has shown that the street-canyon flow appears to be strongly affected by lateral vortices developing near intersections and wakes behind tall buildings at the western end of the study area. Even for perpendicular approach flow, typical 2D-like street canyon vortices can thus be hardly identified. Due to the limited number of sensors available during the field experiments it is also difficult to capture the full complexity of the Park Ave. flow patterns, which was the motivation for an extensive wind-tunnel campaign at the Hamburg University Environmental Wind Tunnel Laboratory (EWTL) in Germany. The paper presents a comparison between the Park Ave. field and wind-tunnel data. The results are qualitatively in good agreement, and the complementary analysis of field and wind-tunnel data provides new insights into flow and dispersion phenomena in complex urban settings.