Building-Resolving Simulations of Dense Gas Dispersion

Large amounts of naturally-occurring and manufactured gases used in chemical industry or for power production are stored and transported in liquefied form in or near densely populated urban environments. When released, liquefied gases are often denser than air, either due to their molecular mass or to the storage conditions (high pressure and lower temperature than that of the ambient air). Accidental or intentional releases and spills of these gases represent a significant hazard. To improve approaches for emergency planning and response in case of dense gas release we need to develop a better understanding of the physical processes and effects associated with dense gas dispersion in complex urban environments. Since outdoor experimental studies require significant resources, high-resolution numerical simulations using computational fluid dynamics (CFD) models represent a complementary tool that enables us to span the space of parameters governing dense gas dispersion.

To address these needs for simulating dense gas dispersion in the urban environment, we have developed and tested a new massively-parallel version of the CFD model FEM3MP. The new version of FEM3MP includes both the dense gas physics (gravity-induced flow, turbulence suppression, heat transfer with the ambient atmosphere) coupled with ambient conditions (wind speed, atmospheric stability, humidity), and the terrain effects (building-induced turbulence, building channeling, gravity effects due to terrain slope, ground characteristics) are explicitly represented.

We demonstrate, analyze, and compare the relative effects of density and buildings on non-isothermal dense gas transport and contrast them to the dispersion of neutrally buoyant gas over complex terrain (including buildings). Finally, we present an initial model validation by comparing simulations to measured concentrations from the Burro 8 experiment in which liquefied natural gas was released at the China Lake test facility.