SPATIAL VARIABILITY OF MEAN FLOW AND TURBULENCE FIELDS IN STREET CANYONS

Air pollution episodes in cities are often related to emissions from traffic. These emissions occur near the ground, and dispersion of the exhaust gases is highly affected by the complex flow phenomena inside the urban canopy. Applied dispersion models must be able to predict the flow patterns observed inside and above the street canyons. During the last few years, the flow and dispersion characteristics in street canyons were investigated in several wind tunnel studies. Two major questions are nevertheless left open: (i) how strong is the influence of the particular wind tunnel setup on the observed characteristics of flow in street canyons, and (ii) to what extent these characteristics can be parameterized? In the present paper, we undertake a comparison of flow parameters measured in three different wind tunnel models of street canyons with idealized geometry and in a detailed model of a real street canyon surrounded by an urban canopy. In all experiments considered, mean values and turbulent statistics of all three velocity components were derived from high-resolution flow measurements. We discuss the spatial variability of the flow and turbulence fields inside and above the canyons, and the influence of urban canopy irregularities on the properties of spatially averaged flow profiles.