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World Trade Center (WTC) Research

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Air Quality Forecasting

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Climate Impact on Air Quality

Fine-Scale Modeling

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NOx Accountability

The collapse of the World Trade Center (WTC) towers brought considerable focus to the need for adequate simulation tools for determining exposure and risk from such catastrophic events. An important first step in a methods development program is to examine the exposure pathways through a reconstruction of the transport and dispersion of pollutants released from the WTC site using available modeling and monitoring approaches. Central to development and evaluation of exposure modeling methods is a laboratory scale model simulation of pollutant transport and dispersion in Lower Manhattan. A 1:600 scale model of Lower Manhattan has been constructed and inserted into the test section of the Fluid Modeling Facility's Meteorological Wind Tunnel.



Fine Scale Modeling

Philadephia Modeling Prototype (PDF, 19 pp, 490KB)About PDF

World Trade Center Disaster Site
Fluid Modeling Facility's Meteorological Wind Tunnel

Fluid Modeling Facility’s Meteorological Wind Tunnel

The model is constructed on a large turntable so that different wind directions may be selected for study. In addition to the many buildings and structures of Lower Manhattan, the model includes a emulation of the WTC rubble pile as it appeared approximately one week after the collapse. Smoke and tracer gas are released from nine positions throughout the simulated sixteen acre site.

WTC rubble pile as it appeared approximately one week after the collapse.

The study design includes smoke visualization for a qualitative examination of dispersion in this very complex urban landscape and detailed measurements of flow characteristics (velocities and turbulence) and concentration distributions within all of Lower Manhattan. Smoke visualizations have been conducted for the due westerly wind direction suggesting a number of interesting flow phenomenon. Among them are vertical venting behind large/tall buildings, channeling down street canyons, and both horizontal and vertical recirculations associated with individual structures and groups of tall and tightly compacted buildings (such as the Wall Street area in the southeast edge of Manhattan).

Natural light is illuminating the smoke.

Examples of neutrally buoyant smoke released from the WTC site with flow from left to right are displayed; natural light is illuminating the smoke and a vertical laser sheet is additionally illuminating the plume near the centerline of source.

Vertical laser sheet is additionally illuminating the plume near the centerline of source.

This shows an example where a significant amount of plume material is vented quickly upward by the tallest buildings in the immediate vicinity of the site. The vertical extent of the resultant plume is, therefore, well above the buildings at the time the material passes beyond the downwind city boundary.

The new Laser Doppler Velocimeter

The velocity and turbulence measurements for the westerly wind directions are just underway. The new Laser Doppler Velocimeter, providing remote measurements of flow and turbulence through optical windows in the tunnel floor, has been successfully inaugurated. A preliminary study was conducted within narrow, two-dimensional model street canyons to determine the critical Reynolds number needed to insure turbulent flow. Using the street canyon width as the appropriate length scale, the critical Reynolds number (above which similarity of turbulence in the model and atmosphere can be assumed) was found to be between 4000 and 5000. In the proposed study of Lower Manhattan, the lowest Re will exceed 10,000 (well above the critical value). The flow measurements will be followed by detailed tracer-concentration measurements throughout the model domain. The entire process will be repeated for other interesting wind directions. Upon completion of the data collection phase in early spring of 2003, the database will be analyzed, documented, and made available to developers for comparison with the simulation results from Computational Fluid Dynamics and other types of models. (Steve Perry, 919 541 1896; Roger Thompson, 919 541 1895)

Atmospheric Modeling

Research & Development | National Exposure Research Laboratory

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