Simulation of Fluid Dynamics Around Complex Urban Geometries

The threat of a chemical and/or biological contaminant release in an urban environment is a major concern to both mili tary and civi l ian sectors. Accurate and detailed modeling of contaminant transport in urban environments that accounts for complex physical processes and varying meteorological conditions is central to any consequence management technology aimed at providing a timely, effective response to a chemical or biological threat. To facilitate necessary improvements to contaminant transport models being applied to this class of problems, it is important to assess the ability of a given numerical model to predict atmospheric transport and dispersion around single and multiple complex buildings. Such assessments can be derived from calibration and validation studies that rely on experimental data, and numerical sensitivity studies of computational parameters. In this paper, we present the status of three ongoing Computational Fluid Dynamics modeling init iat ives, supported in part by High Performance Computing Challenge resources, and focus on the important f luid dynamic issues. The threedimensional, time-dependent computational studies are performed using FAST3D-CT, an extension of the Naval Research Laboratory's scalable FAST3D model Research Aerospace Engineer. Code 6410. Senior Member A I A A 'Chief Scientist and Director. Code 6400. Fellow A IA A ' Re search Physicist, Code 6440 'Research Physicist Code 6440 ^Staff Scientist This paper is declared a work of the U.S. Government and is not subject to copyright protection in the Uni ted States. to contaminant transport problems for urban and environmental hazard assessment. The first initiative involves a validation study of flow over a surfacemounted cube using existing wind tunnel and water tank databases. The second investigates the effects of inflow velocity characteristics on flow patterns around a complex full-scale building. This is accomplished through a series of calibration studies using field test data and numerical sensitivity studies. The third initiative focuses on the simulation of single and multiple releases driven by prescribed and forecasted winds through a multi-kilometer section of a model city resembling downtown Washington, DC. This third initiative has led to the development of a zerolatency, model-based approach to sensor integration for the protection of single and/or multiple facilities in high-density urban environments.