High-Resolution CFD Simulation Of Airflow and Tracer Dispersion In New York City

In 2004, a research project - the New York City Urban Dispersion Program (NYC UDP) -was launched by the Department of Homeland Security with the goal to improve the permanent network of wind stations in and around New York City and to enhance the city's emergency response capabilities. Encompassing both field studies and computer modeling, one of the program's objectives is to improve and validate urban dispersion models using the data collected from field studies and to transfer the improved capabilities to NYC emergency agencies. The first field study was conducted in March 2005 and two additional studies will occur in 2005 and 2006. Concurrently model simulations, using simple to sophisticated computational fluid dynamics (CFD) models, have been performed to aid the planning of field studies and also to evaluate the performance of such models.

Airflow and tracer dispersion in urban areas such as NYC are extremely complicated. Some of the contributing factors are complex geometry, variable terrain, coupling with larger scale flows, deep canyon mixing and updrafts/downdrafts due to large buildings, street channeling and upstream transport, roof features, and heating effects, etc. Our CFD model, FEM3MP, has been developed to address some of the above complexities. It is based on solving the three-dimensional, time-dependent, incompressible Navier-Stokes equations with appropriate physics for modeling airflow and dispersion in the urban environment. Also utilized in the model are finite-element discretization for effective treatment of complex geometries and a semi-implicit projection method for efficient time-integration.

Predictions from our model are continuously being verified against data from field studies, such as URBAN 2000 and the Joint URBAN 2003 experiments. Recently our model was also used to perform simulations to support the planning of the UDP field experiments. In this study, flow and dispersion simulations will be conducted for a subset of the field experiments, a model-data comparison will be performed, and major findings will be reported at the conference.

Acknowledgement. This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.