ASSESSMENT OF VELOCITY AND TURBULENCE BOUNDARY CONDITION TREATMENTS UPON THE IN-CANOPY WIND, TURBULENCE AND TRANSPORT AND DISPERSION BEHAVIOR IN MIDTOWN MANHATTAN

In this paper, we summarize the results of a study showing the effects of specifying different approaching velocity and turbulence profiles upon the wind, turbulence and transport and dispersion behavior in Midtown Manhattan. Three different, commonly used velocity and turbulence profiles are implemented to specify the farfield boundary conditions for a Computational Fluid Dynamics-based, urban area transport and dispersion model, CFD-Urban. The transport and dispersion behavior from these different profiles is compared and contrasted, and the effect of mesh density and location of the far-field boundaries is also assessed. The three profiles used in this comparative study are logarithmic, Monin-Obukhov and Urban Canopy Model (UCM). The turbulence quantities derived for these three profiles is an important, controlling parameter with regards to the dispersion behavior, and we show how turbulence profiles that are in turbulence equilibrium are derived for each, and compare volumetrically-averaged velocity and turbulence profiles at various locations, deep within the urban area. The intent of the study is to address some commonly asked questions: What is the effect of the prevailing conditions upon the transport behavior in a dense, deep canyon city, such as Midtown Manhattan? How sensitive are the in-canopy velocity and turbulence profiles to the prevailing/boundary conditions? We will address these issues with this paper.

Acknowledgements The authors gratefully acknowledge the financial support for the MSG05 and UDP CFD calculations from the Defense Threat Reduction Agency (Mr. Rick Fry) and the US Army Dugway Proving Ground (Mr. Jim Bowers).