1041 PIV STUDY OF VORTEX BREAKDOWN IN LOWAND HIGH-SWIRL JETS AND LEAN FLAMES

Abstract

The present work is devoted to a comparative study of low-and high-swirl flows in a model lean combustor. Lean methane-air mixture with equivalence ratio of 0.6 burned at atmospheric pressure. A high-repetition stereoscopic PIV system was used for the velocity measurements both in the reacting and non-reacting flows. During analysis of the velocity data sets, the emphasis was put on application of statistical tools to build a reduced model of flows as stochastic dynamical systems. Proper orthogonal decomposition and dynamic mode decomposition routines were used in the study. It was observed that despite the combustion significantly affected the time-averaged characteristics of the strongly swirling flow, the dynamics of both flows were associated with a global helical instability mode, which corresponded to a strong precession of the vortex core. In contrast, velocity fluctuations above the nozzle exit of the studied low-swirl flows were associated with local instability modes. In particular, this result indicates that the low-swirl flame should be more sensitive to external flow perturbations for combustion control.