Wind fields and turbulence statistics in an urban street canyon

This is the first paper of a long-term measurement campaign to explore wind, temperature, radiation and energy fields within an urban canyon. A canyon and a rooftop mast were installed in a canyon with an aspect ratio (Height/Width) of 2.1 in Göteborg, Sweden. A number of instruments including sonic anemometers, radiometers and thermocouples were mounted in vertical profiles and across the width of the canyon. The experimental set-up, the characteristics of the canyon flow pattern and mean and turbulence statistics with respect to above canyon flow are examined using data collected under clear-sky conditions in summer and autumn 2003. Results show that under cross-canyon (within 60° of orthogonal) flow, a single helical vortex exists. High temporal resolution analysis suggests that eddies frequently penetrate the shear stress layer at the canyon top disrupting established flow patterns. A combination of complex building roof shapes and local topography may contribute to this effect by maintaining a high degree of turbulence. The profile of mean wind speed within the canyon and the relation with that above canyon depends on the ambient flow direction in relation to the canyon long axis. Turbulence statistics show results similar to other field studies, with turbulence kinetic energy and vertical mixing greatest toward the windward wall.