Computational Fluid Dynamics Modeling of Urban Dispersion at Neighborhood Scale Validated with Tracer Data from Joint Urban 2003

During the Joint Urban 2003 field campaign, a 90 m wind speed and tracer concentration vertical profile system was erected approximately 1 km from the tracer release. During study periods, continuous 5-minute averaged concentrations of SF6 tracer gas were measured at 7 heights, from 10 to 75 meters above ground level. The vertical profile results show that tracer is relatively well-mixed through the depth of the measurements, and that most of the variation in tracer concentration observed in the profile time series is related to changes in wind direction as opposed to changes in vertical turbulence profiles. These vertical profile data along with other surface tracer concentration and turbulence data are compared to preliminary simulation results obtained using the computational fluid dynamics FLUENT model, a commercially available CFD package. At this urban scale, the upwind structures are represented as simplified blocks with appropriate heights and footprints. Characterization of dispersion at this distance yields information concerning the bulk turbulence generated by the downtown buildings, the rate at which pollutants are removed from the downtown core, and the spatial extent of hazardous pollutant concentrations.