Pentagon Shield
A sample of ground level CFD winds is shown in this figure. The image is from the two-dimensional user interface. Modification of a southeasterly wind by the building is clearly seen. Of particular note is the reversal of flow within the central courtyard
Pentagon Shield is a targeted emergency response transport and dispersion program designed to deal with accidental and intentional releases of hazardous materials into the urban atmosphere. The program consists of two components: The first is the development of an emergency response building-protection system and the second is both an investigation of turbulence characteristics in the urban environment and an evaluation of the transport and dispersion modeling components.
FY06 Accomplishments:
Development of the prototype Pentagon Building Protection System is complete. The system incorporates observational data feeds from Doppler radar and Doppler lidar, analysis of 3-dimensional wind fields from Doppler radial winds using VDRAS and VLAS, and numerical weather prediction capabilities from regional to metro scale. This prototype system provides a new ability to detect chemical and aerosol/particulate releases and predict the transport and dispersion of those releases. The prototype building protection system was successfully demonstrated in field trials early in FY 2006, and validation studies indicate that the prototype system did an excellent job of simulating the transport and dispersion of contaminant releases within an urban environment. To facilitate future development in this area, RAL also developed an urban transport and dispersion test bed in which to develop new applications and showcase work in progress.
An evaluation of transport and dispersion models was also conducted using field observations of a sulfur hexafluoride (SF6) tracer from an elevated line sources and the Urban Hazard Prediction and Assessment Capability (Urban HPAC) model. The evaluation showed that the general Urban HPAC concentration variation with distance was approximately correct, except for some stability-related biases, and that there was more statistical variability in the observations than in the predictions. The second point is consistent with model evaluations conducted elsewhere, and the variability is attributed primarily to the inherent random variability in the turbulent dispersion process. In related work, an investigation of the nighttime meteorology in suburban Arlington, Virginia, documented the existence of a stable boundary layer (SBL) in that area. This work is shedding new light on dispersion conditions in urban/suburban areas, contradicting the popular belief within the dispersion modeling community that near-neutral conditions always prevail at night.
Plans for FY07:
Work will focus on transitioning from a prototype building protection system to an operational system for deployment at the Pentagon. Work on optimizing the execution speed of the component models will continue. The CFD model and the transport and dispersion model will both be expanded to cover a 12 by 15 kilometer area surrounding much of the National Capitol Region. The urban transport and dispersion test bed will also be expanded to incorporate RTFDDA and advanced CFD capabilities.
Impact of the Program:
The scientific understanding and technologies developed and deployed at the Pentagon will not only help protect the more than 20,000 persons who work at that facility, but they can also be applied in many other situations for the protection of urban populations and facilities against airborne hazards.