Mechanism of buoyant turbulent diffusion flames

Abstract

The paper addresses the basic combustion mechanism of buoyant turbulent diffusion flames with emphasis on flame generated turbulence. The vorticity equation and Kelvin's theorem show that the buoyant generation of vorticity and its dissipation within the flamelets drives the combustion of fuel and oxidant in buoyant turbulent flames, characteristic of fires. It is an example of a Rayleigh-Taylor instability mechanism characterized by a constant Rayleigh number. The mechanism explains why measured volumetric heat release rates and radiant fractions are constants and independent of the overall fire size. It conforms to the fundamental requirement that the volumetric heat release be proportional to p g. The paper presents the cascades of vorticity as well as rotational and translational turbulent kinetic energies. A set of modified LES equations using the EDC concept are suggested for simulating buoyant turbulent diffusion flames that should yield mesh-size independent solutions. © 2013 International Association for Fire Safety Science.