CFD Modeling for Urban Area Contaminant Transport and Dispersion: Model Description and Data Requirements

Computational Fluid Dynamics (CFD) modeling for urban area wind, turbulence and contaminant transport and dispersion is becoming more accepted by the community as a useful means to understand the complex flow behavior in urban areas. As shown in a companion paper presented at this conference, urban areas, such as New York City, may exhibit localized, intense vertical mixing and lateral spreading behavior that is highly dependent upon building shapes, sizes, locations, and prevailing wind conditions and that small changes in contaminant source locations can produce quite different contaminant spreading behavior. This paper describes a model that has been developed to simulate the wind, turbulence and dispersion in urban areas on the building to city blocks scale, and summarizes the data typically needed to perform the simulations. In particular, the finite-volume, Reynolds-Averaged Navier-Stokes formulation of the model is described, as well as different techniques that are used to model buildings both explicitly (by resolving the building surfaces) and implicitly (by introducing momentum and turbulence source terms to represent building effects upon the flow fields). Turbulence closure using a standard and a Renormalization Group variant of the k-e model is described, including modifications to the turbulence model and boundary conditions to better represent atmospheric boundary layers. Data requirements for this model are defined, including; flow and turbulence boundary conditions, building geometric descriptions, contaminant source description. Recommendations for data to be included in a community-wide urban database are made to allow the more widespread usage of CFD-based modeling.

Acknowledgements The authors gratefully acknowledge the financial support for this work from the Defense Threat Reduction Agency, Technology Development Directorate/TDOC, Technical Monitor Mr. Rick Fry.