The application of Computational Fluid Dynamics (CFD) to the understanding of urban wind flow and dispersion processes has gained increasing attention over recent years. While many of the simpler dispersion models are based on a set of prescribed meteorology to calculate dispersion, the CFD approach has the ability of coupling the wind field to dispersion processes. This has distinct advantages when very detailed results are required, such as for the case where the releases occur around buildings and within urban areas. CFD also has great flexibility as a testbed for turbulence models, which has important implications for atmospheric dispersion problems.

In the Fall of 1999, a series of dispersion field experiments (URBAN 2000) were conducted at Salt Lake City, Utah. The purpose of these experiments was to provide field data for evaluation of CFD as well as for other dispersion models. Initially several CFD modeling studies were performed to provide guidance for the experimental team in the selection of release sites and in the deployment of wind and concentration sensors. Our recent CFD calculations were focused on the near field of the release point. The proximity of the source to a large commercial building and to the neighboring buildings several of which have multi-stories, present a significant challenge even for CFD calculations involving as fine as 1 meter grid resolutions. Since the atmospheric releases were conducted during the late evening and the early morning periods, the ambient wind speeds were generally quite low and are frequently impacted by locally driven flows away from the metropolitan area.

In this paper we will present results of a modeling study based on one or more experiments where field data is available. Comparisons will be made between model results and field data for both the wind fields as well as concentrations.

This work was performed under the auspices of the U. S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.

References

Brown, M., M. Leach, R. Calhoun, W.S. Smith, D. Stevens, J. Reisner, R. Lee, N.-H. Chin, & D. DeCroix, 2001: Multiscale modeling of air flow in Salt Lake City and the surrounding region, ASCE Structures Congress 2001, Wash. DC, LA-UR-01-509.

Lee, R. L., R. Calhoun, S. Chan, J. Leone, and D. Stevens, 2000: Modeling of Building Scale Flow and Dispersion, Third Int. Symposium on Environmental Hydraulics, Arizona State University, Tempe, AZ, Dec. 5-8, 2001.