PNNL

Abstract

A 3D computational fluid dynamics study using Reynolds averaged Navier-Stokes modeling was conducted and validated with field data from the Joint Urban 2003 dispersion study in Oklahoma City. The modeled flow field indicated that the many short buildings in this domain had a relatively small effect on the flow field, while the few tall buildings drove the transport and dispersion of tracer gas through the domain. Modeled concentrations and wind speeds were compared to observations along a vertical profile located about 500 meters downwind of the source. The isothermal base case using the k-epsilon closure model was within 50% of the field measurements, while a convective case with ground and building surfaces 10 degrees C hotter than ambient temperatures improved the modeled profile to within 30% of observations. Varying wind direction and source location had a significant effect on the plume dispersion due to the irregularity of the urban landscape. The location of the tallest obstacle in this domain with respect to the source position defined the size and shape of tracer plumes in this study. Model results based upon a Reynolds stress closure scheme were also compared to the vertical concentration profiles. For this location, the isothermal case underestimated concentrations; however, the case with thermal buoyancy resulted in concentrations within 25% of the observations.