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Steven R. Hanna, Michael J. Brown, Fernando E. Camelli, Stevens T. Chan, William J. Coirier, Olav R. Hansen, Alan H. Huber, Sura Kim, and R. Michael Reynolds

Computational fluid dynamics (CFD) model simulations of urban boundary layers have improved in speed and accuracy so that they are useful in assisting in planning emergency response activities related to releases of chemical or biological agents into the atmosphere in large cities such as New York, New York. In this paper, five CFD models [CFD-Urban, Finite Element Flow (FEFLO), Finite Element Model in 3D and Massively-Parallel version (FEM3MP), FLACS, and FLUENT–Environmental Protection Agency (FLUENT-EPA)] have been applied to the same 3D building data and geographic domain in Manhattan, using approximately the same wind input conditions. Wind flow observations are available from the Madison Square Garden 2005 (MSG05) field experiment. Plots of the CFD models' simulations and the observations of near-surface wind fields lead to the qualitative conclusion that the models generally agree with each other and with field observations over most parts of the computational domain, within typical atmospheric uncertainties of a factor of 2. The results are useful to emergency responders, suggesting, for example, that transport of a release at street level in a large city could extend for a few blocks in the upwind and crosswind directions. There are still key differences among the models for certain parts of the domain. Further examination of the differences among the models and the observations are necessary in order to understand the causal relationships.

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