Fast and Accurate Urban Aerodynamics for Civil Defense in Cities ( More about this event )
Speaker: Jay P. Boris, United States Naval Research Laboratory
Department: Mechanical & Aerospace Engineering
Location: Engineering Quadrangle J223
Date/Time: Friday, December 7, 2012, 3:30 p.m. - 4:30 p.m.
Fast and Accurate Urban Aerodynamics for Civil Defense in cities
Dr. Jay Boris, Chief Scientist, Code 6003
United States Naval Research Laboratory
ABSTRACT: Urban airflow accompanied by contaminant transport (CT) presents new, extremely challenging modeling requirements best met using complex-geometry simulation tools developed by the aerospace industry. Urban aerodynamics deals with com¬plex geometries, highly turbulent flows, and unsteady buoyant flow physics. Crucial technical issues that need to be addressed include time-dependent turbulent fluid transport (aerodynamics) coupled to environmental boundary condition modeling (meteorology). The advantages of the Computational Fluid Dynamics (CFD) approach and the Large Eddy Simulation (LES) representation include the ability to quantify complex geometry effects, to predict dynamic nonlinear processes faithfully, and to treat turbulent problems reliably in regimes where experiments, and therefore model validations, are impossible or impractical. NRLs FAST3D-CT three-dimensional urban aerodynamics model is based on the scalable, high-order, low dissipation Flux-Corrected Transport convection algorithm. The model also incorporates a stratified urban boundary layer with realistic wind fluctuations, solar heating including shadows from buildings and trees, aerodynamic drag and heat losses due to the presence of trees, surface heat variations and turbulent heat transport.
Since accuracy alone is not enough, we have developed a methodology for using very high fidelity Monotone Integrated Large Eddy Simulations (MILES) to drive a much faster-than-real-time contaminant transport model for crisis management. The system called CT-Analyst®, based on urban aerodynamics computations, has been developed, tested, and deployed to evaluate windborne Contaminant Transport (CT) threats and to aid in time-critical civil defense decisions in cities where current transport and dispersion methods are too slow and inaccurate. Designed for the military prior to 9/11, CT-Analyst can incorporate verbal reports, handle input from fixed and mobile sensors, and functions in realistic emergencies where the nature, amount, and location of an airborne contaminant source or Chemical, Biological, Radiological (CBR) agent is unknown and where the wind fields are dynamic and complicated by the city geometry. CT-Analyst is well suited to urban and site defense in the homeland Security context.