Analysis of the Large Urban Fire Environment. Part I. Theory

摘要

The strongly buoyant flow generated in and around a large area fire is analyzed. Jump conditions applicable at the fire periphery are used to effect model problem closure, thus permitting calculations 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, the model equations can be solved exactly. The resulting solution concisely describes the basic interchanges of energy and momentum as well as the role of pressure gradients in fire-wind generation. In general, the localized analysis provides a framework for detailed studies of the complex physics of fire-generated flows without recourse to extensive numerical computations involving the far field. The analysis is applied in simulations of the 'turning region' environment created by (1) an experimental, multiple-fuel-bed Flambeau fire, and (2) the World War II Hamburg firestorm. Computed results duplicate observed flow patterns and are consistent with reported data. (Author)