Flow Patterns at the Ends of a Street Canyon: Measurements from the Joint Urban 2003 Field Experiment

During the Joint Urban 2003 experiment held in Oklahoma City, Oklahoma, an east–west-running street canyon was heavily instrumented with wind sensors. In this paper, the flow patterns at the street canyon ends are investigated by looking at sonic anemometers placed near ground level and tethersonde wind vane systems operated in “ladder” mode that were suspended over the sides of the buildings on each side of the street. For southerly flow conditions, the street-level wind sensors often showed what appeared to be a horizontally rotating “corner” or “end” vortex existing at each end of the street canyon near the intersections. It was found that this vortex flow pattern appeared for a wide range of upper-level wind directions but then changed to purely unidirectional flow for wind directions that were outside this range. The tethersonde wind vane measurements show that this vortexlike flow regime occasionally existed through the entire depth of the street canyon. The horizontal extent of the end vortex into the street canyon was found to be different at each end of the street. Under high-wind conditions, the mean wind patterns in the street did not vary appreciably during the day and night. The end vortex may be important in the dispersal of airborne contaminants, acting to enhance lateral and vertical mixing.