Numerical and physical modeling of bluff body flow and dispersion in urban street canyons

To develop reliable computer models for the bluff body flow and transport of pollutants or chemical and biological (CB) agents in urban environments requires accurate measurements of the basic flow fields for carefully controlled, well-known conditions. Fluid modeling in an industrial wind tunnel provides an opportunity to produce accurate simulations of the bluff body flow and transport of urban pollution or of CB agents associated with urban terrorism incidents. A basic building shape, the Wind Engineering Research Field Laboratory building (WERFL) at Texas Tech University, is used for this study. The urban street canyon was represented by a 1:50 scale WERFL model that was surrounded by models of similar dimensions. These buildings were arranged in various symmetric configurations with different separation distances and different numbers of surrounding building. A series of measurements is made over a generic urban street canyon arrangement using flow visualization, anemometry, pressure transducer and gas chromatography. The experimental data include visualization, velocity and turbulence intensity profiles, surface pressure on the building and dispersion of releasing gas. Results are compared to three-dimensional numerical models of the same configuration using the commercial code, FLUENT 5.3. The effects of grid resolution, boundary conditions, source placement and selection of turbulence model (kappa-epsilon, RNG kappa-epsilon, Reynolds stress, etc.) are examined in a series of sensitivity calculations.