Asymptotically Large Area Fires

Abstract

The fluid dynamics of large area fires is considered. The modeling of such fires using asymptotic plume theories, rotating plume theories, and hydrocode simulations is briefly reviewed, and a new model describing the strongly buoyant flow of the burning region and its transition to a weakly buoyant, free-convection column is presented. The new model simulates combustion processes by a volume heat addition, and allows large changes in density and temperature. Jump conditions applicable at the fire periphery are used to effect model problem closure, thus permitting calculation of the induced fire winds independent of a far-field analysis. Sample results show the turning and decay of a high-velocity inflow to form a nearly vertical flow, and illustrate how the generation of high-velocity fire winds is affected by the dimensions of the burning region, heat release, and the production of buoyancy and pressure gradients.