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APPLICATIONS OF CFD SIMULATIONS OF POLLUTANT TRANSPORT AND DISPERSION WITHIN AMBIENT URBAN BUILDING ENVIRONMENTS: INCLUDING HOMELAND SECURITY
Citation:
HUBER, A. H., M. FREEMAN, R. SPENCER, B. BELL, K. KUEHLERT, AND W. SCHWARZ. APPLICATIONS OF CFD SIMULATIONS OF POLLUTANT TRANSPORT AND DISPERSION WITHIN AMBIENT URBAN BUILDING ENVIRONMENTS: INCLUDING HOMELAND SECURITY. Presented at Air and Waste Management Assocaition 98th Annual Conference, Minneapolis, MN, June 21 - 25, 2005.
Impact/Purpose:
The objective of this task is to improve EPA's ability to accurately predict the concentrations and deposition of air pollutants in the atmosphere that are known or suspected to cause cancer or other serious health effects to humans, or adverse environmental effects. It is an essential component of EPA's National Air Toxics Assessment (NATA), which seeks to identify and quantify the concentrations and sources of those hazardous air pollutants which are of greatest potential concern, in terms of contribution to population risk. It is a major contributor to NERL's Air Toxics Research Program.
"Air toxics" or "hazardous air pollutants" (HAPs) is a category that covers a large variety of chemicals, which range from relatively non reactive to extremely reactive; can exist in the gas, aqueous, and/or particle phases; display a large range of volatilities; experience varying deposition velocities, including in some cases revolatilization; and are emitted from a wide variety of sources at a large variety of different scales. In addition, concentrations of air toxics are needed by regulators for both short (days) as well as long (up to a year) time scales. These requirements challenge our current capabilities in air quality models far beyond the needs for other pollutants, such as ozone. The specific work being done under this task involves 1.) developing and testing chemical mechanisms which are appropriate for describing the chemistry of air toxics; 2.) incorporating these chemical and physical mechanisms into EPA's CMAQ modeling system and applying the model at a variety of scales; and 3.) developing the methods for using models to predict HAPs concentrations at subgrid or neighborhood scales; and 4.) using these tools to assess the magnitude and variability of concentrations to which urban populations are exposed.
Description:
There is presently much focus on Homeland Security and the need to understand how potential sources of toxic material are transported and dispersed in the urban environment. Material transport and dispersion within these urban centers is highly influenced by the buildings. Computational Fluid Dynamics (CFD) simulations have emerged as a promising technology for supporting such assessments, in part due to the advancing power of computational hardware and software. CFD simulations have the potential to yield more detailed simulations than other modeling methodologies because they are a solution of the fundamental physics equations and include the effects of detailed three-dimensional geometry and local environmental conditions. However, the tools are not well evaluated for environmental modeling and best-practice methodologies have not been established. The US Environmental Protection Agency has been developing and evaluating CFD applications for routine air quality studies. Following the events on September 11, 2001, this work has focused on understanding the potential pollution transport and dispersion from the collapse of the World Trade Center towers and the subsequent weeks while fires continued to burn at "ground zero". This work is ongoing and is being extended to support homeland security related studies in other parts of Manhattan.
The results of CFD simulations can both be directly used to better understand specific case studies as well as be used to support the development of more simplified algorithms that may be generally applied. Detailed CFD simulations make it possible to safely explore potential scenarios in support of preparedness, location of monitoring instrumentation and better understanding air measurements. This presentation summarizes ongoing developments and applications of CFD simulations through case studies using the commercial FLUENT CFD software code. Pollutant transport and dispersion in the ambient environment is being simulated. Plans have been initiated to develop methods to interface with indoor air quality.
Future wind tunnel and field studies should play a critical role in supporting CFD developments by providing opportunities for CFD simulation evaluation and demonstration of reliability. The process should be iterative in that a better CFD model provides better guidance for collecting better measurements. Even the best conceivable field measurement study will have very few data relative to the detailed structure of air flow and pollutant dispersion within the complex built urban environments. Therefore application of CFD simulations is critical to being able to understand pollutant transport and dispersion within urban building environments, and consequently critical in support of homeland security.