Three-dimensional Modeling of Combustion and Pollution from Wildland Fires

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This research represents a joint initiative between the University of Colorado, the National Center for Atmospheric Research (NCAR), and the Intermountain Fire Sciences Laboratory of the U.S. Department of Agriculture Forest Service in Missoula, Montana, to significantly improve existing capabilities to model atmosphere-fire coupling as might occur during intense burning in wildland fires. Specific tasks will include: (1) Development of subgrid scale models for turbulent combustion based on a description of the flame surface area. This will enable a more accurate treatment of fluid dynamic-combustion interactions. (2) Vertically and horizontally aligned vorticity can act as means of lofting and ejecting burning material from the fire that could lead to spotting. Initially, using post-processed velocity fields from NCAR's existing atmosphere-fire model, a Lagrangian treatment of lofting, aerodynamics and settling of firebrands will be carried out. Using this, a suitable Eulerian model will be developed. (3) A simplified model to describe drying, pyrolysis, and char oxidation from a solid fuel bed will be developed, based on basic conservation principles. (4) Lastly, a simplified smoke model that will allow quantification of carbon monoxide and particulate concentrations will be developed. This is an important component that will assist with model evaluation and to test alternative smoke management scenarios.The sub-models developed will be integrated into an existing three-dimensional, mesoscale large eddy simulation that has been under development for twenty years at NCAR, with recent collaboration with the Intermountain Fire Sciences Laboratory. Recently completed and ongoing field experiments will provide observations on fires of opportunity ranging in scale from sub-meter to kilometers using a digital infrared camera. With available data these experimental results will be used as a test bed for the fully integrated model. Results are expected to assist forest management agencies to improve fire-fighting strategies and for planning prescribed burns. These advances will have a fundamental impact on the scientific community working in the areas of turbulent combustion and pollution modeling.