Releases and spills of dense gases represent significant hazard particularly in densely populated urban environments. Better understanding of the physical processes and effects associated with dense gas dispersion in complex urban environments is needed to improve approaches for emergency planning and response in case of a release. To achieve this goal we study dense gas dispersion over complex terrain using large-eddy simulations (LES). We carry out LES of dense gas dispersion using our urban dispersion model FEM3MP, which we have recently extended to dense gas applications. Here we present validation of FEM3MP model using data from Petroleum Environmental Research Forum (PERF) Kit Fox field study. This field study took place in 1995 at the Nevada Test Site. The Kit Fox field study consisted of releases of carbon dioxide over a desert environment that was modified to represent an industrial facility by introduction of two types of obstacles. A dry lake bed was covered with small, billboard-type obstacles. Into this small-obstacle array, an array of larger obstacles was imbedded. We treated small obstacles as surface roughness while fully resolving large obstacles. We carried out LES using both the Smagorinsky subgrid model (Lilly, 1967) and the nonlinear subgrid model (Kosoviæ, 1997). In addition to evaluating the effects of surface roughness on dense gas dispersion, we also explore the effect of atmospheric stability using data from Kit Fox releases carried out during neutral and stable atmospheric conditions.

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS- 405692