Eulerian numerical modeling of contaminant transport in Lower Manhattan, New York City, from a point-source release under the dominant wind condition: Insights gained via LES

Released pollutants and poisonous chemicals in the highly-populated urban areas can spread via wind flow and affect the health, safety, and wellbeing of those close to the source and others downstream. Being able to predict the transport of airborne contaminants in such urban areas could help stakeholders to plan emergency responses. Airflow due to the wind in urban areas with closely packed buildings results in complicated aerodynamics around buildings that, in turn, can lead to intricate contaminant transport phenomena. We conduct high-resolution large-eddy simulation (LES) of airflow in Southern Manhattan, a highly-populated area in New York City, due to a dominant wind blowing from south to north. The LES results show complex flow dynamics around the buildings of various heights and, consequently, complicated contaminant transport processes from a source-point which is located in front of the New York Stock Exchange building at 30 m above ground. The flow tends to align with the streets that are fairly parallel to the wind direction creating high-velocity core regions, while the airflow loses its momentum markedly farther downwind in the urban area. For as long as the source of contamination exists, the pollution plume rapidly travels through the streets reaching downwind areas. When the source is removed, contaminants that are trapped in the low-momentum urban area linger to exit the flow domain.