Analysis of the burning region and plume of a large fire. Technical report, 26 November 1984-26 February 1986

The strongly buoyant flow generated in and around a large area fire is analyzed. Jump conditions applicable at the fire periphery are used to affect model-problem closure, thus permitting calculation of induced fire winds independent of a far-field analysis. Combustion processes are modeled by a volume heat addition. The induced flow is compressible, with arbitrary changes in temperature and density allowed. In one parameter limit, a closed-form solution is developed that concisely describes the basic interchanges of energy and momentum as well as the role of pressure gradients in fire-wind generation. The full analysis is applied in simulation of the hydrothermodynamics of a multiple-fuel-bed Flambeau fire. Computed results duplicate observed flow patterns. A parametric analysis explores the influence of combustion-zone dimensions, heating rate, radiation, and turbulent diffusion on the solution for even larger fires. Next, hydrocode solutions are presented for fires of city size with radii of several kilometers and flame heights of 100 m. The atmospheric response as a function of time is illustrated. Vortex motions generated by the fire influence both the inflow and plume structure. A fairly persistent circulatory flow develops below the tropopause. Periodically, however, the tropopause is penetrated, and an upper-level counter-rotating flow develops thatmore » may contain some combustion products from the central fire region. Results suggest the formation of distinct smoke strata in the lower atmosphere, with some particulate and aerosol mass entering the stratosphere.« less