Large eddy simulation (LES) using the model FAST3D-CT showing contaminant release near Rockefeller Center, NYC. Winds are from the west, and Bryant Park and the NYC public library are visible in the foreground. The model has 6-m horizontal and vertical resolution. FAST3D-CT was developed by the Laboratory for Computational Physics and Fluid Dynamics (led by Jay Boris) at the Naval Research Laboratory in Washington DC.
Our work quantitatively assesses the spatial extent of modeled contaminated regions resulting from hypothetical airborne agent releases in major urban areas. We compare statistics from a release at several different sites in
Washington DC and Chicago using a Gaussian puff model (SCIPUFF, version 1.3, with urban parameter settings) and a building-resolving computational fluid dynamics (CFD) model (FAST3D-CT). For a neutrally buoyant gas source term with urban meteorology, we compare near-surface dosage values within several kilometers of the release during the first half hour, before the gas is dispersed beyond the critical lethal level. The taller, denser and more variable building landscape of Chicago created increased sensitivity to release site and led to greater divergence in FAST3D-CT and SCIPUFF results relative to the flatter, sparser and more uniform urban morphology of Washington DC.
In our most recent work we are initializing FAST3D-CT with potential temperature and wind velocity from our 0.44 km COAMPS nest centered on Manhattan. Initializing with a mesoscale model that includes urban effects affords a more accurate representation of the local atmospheric boundary layer. The mesoscale model also contains some spatial variability within midtown Manhattan that is communicated to the FAST3D-CT grid at initialization.
Pullen, J., J. Boris, T. Young, G. Patnaik, and John Iselin, “A comparison of contaminant plume statistics from a Gaussian puff and urban CFD model for two large cities,” Atmospheric Environment, 39, 1049-1068, 2005 (pdf)