A Computational Fluid Dynamics Approach for Urban Area Transport and Dispersion Modeling |
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Authors: | Email author" target="_blank">W?J?CoirierEmail author D?M?Fricker M?Furmanczyk S?Kim |
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Institution: | (1) CFD Research Corporation, 215 Wynn Drive, Huntsville, AL, U.S.A |
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Abstract: | A simulation tool has been developed to model the wind fields, turbulence fields, and the dispersion of Chemical, Biological,
Radiological and Nuclear (CBRN) substances in urban areas on the building to city blocks scale. A Computational Fluid Dynamics
(CFD) approach has been taken that naturally accounts for critical flow and dispersion processes in urban areas, such as channeling,
lofting, vertical mixing and turbulence, by solving the steady-state, Reynolds-Averaged Navier–Stokes (RANS) equations. Rapid
generation of high quality cityscape volume meshes is attained by a unique voxel-based model generator that directly interfaces
with common Geographic Information Systems (GIS) file formats. The flow and turbulence fields are obtained by solving the
steady-state RANS equations using a collocated, pressure-based approach formulated for unstructured and polyhedral mesh elements.
Turbulence modeling is based upon the Renormalization Group variant of the k–ε model (k–ε RNG). Neutrally buoyant simulations are made by prescribing velocity boundary condition profiles found by a power–law relationship,
while turbulence quantities boundary conditions are defined by a prescribed mixing length in conjunction with the assumption
of turbulence equilibrium. Dispersion fields are computed by solving an unsteady transport equation of a dilute gas, formulated
in a Eulerian framework, using the velocity and turbulence fields found from the steady-state RANS solution. In this paper
the model is explained and detailed comparisons of predicted to experimentally obtained velocity, turbulence and dispersion
fields are made to neutrally stable wind tunnel and hydraulic flume experiments. |
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Keywords: | Urban area transport and dispersion computational fluid dynamics |
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