Large-eddy simulation of dominant wind and contaminate transport in New York City

The danger of pollutants, biological agents and poisonous chemicals released in urban locations has become a major concern for public safety. While past studies have investigated contaminant transport in small city sections, this research seeks to address the transport of a point-source pollutant in a 3 km-long and highly-populated area of the Lower Manhattan. The study area includes southern Manhattan from the southern tip north all the way to Canal St. A computational grid system with approximately 76 million grid points is used to resolve the flow while the immersed boundary method is employed to resolve the geometry of the buildings, roads, and other objects including many skyscrapers of varying heights. The large-eddy simulation method is used to resolve the wind flow within the urban area. A Eulerian transport model is coupled with LES to compute the concentration field of the pollutant. We found that the pollutant propagates downwind at 42% of the prevailing wind velocity of 3.6 m/s. Once the pollutant source is removed, the pollutant plume propagates out of the study area at 20% of the prevailing wind velocity.