PRELIMINARY-RESULTS OF A NUMERICAL EXPERIMENTAL-STUDY OF THE DYNAMIC STRUCTURE OF A BUOYANT JET DIFFUSION FLAME

Preliminary results of a joint numerical-experimental investigation of the dynamic structure of a buoyant jet diffusion flame are presented. The purpose of this effort is to determine the nature of the unsteady interactions between flames and their associated vortex motions. A direct numerical simulation of an unsteady low-speed propane-air jet diffusion flame is carried out utilizing the flame sheet and conserved variable approximations. Counterrotating vortex structures internal and external to the flame surface appear and move upward along with flame sheet bulges. Tip-cutting (flickering) occurs with a frequency of 11-15 Hz. These dynamic features bear close resemblance to those observed experimentally by means of the rective Mie scattering (RMS) technique. Comparisons between computational and experimental (determined using thin filament pyrometry) near-instantaneous radial temperature profiles at four heights in the flame also show good agreement. The assumption of zero gravity in the computation results in the complete cessation of dynamical activity, thus demonstrating the important role that buoyancy plays in the behavior of this flame.