Experimental characterization of flame/flow dynamics during transition between stable and thermo-acoustically unstable conditions in a gas turbine model combustor

This paper presents an experimental study of the flame/flow dynamics in a single-element, swirl-stabilized, lean premixed pre-vaporized gas turbine model combustor under spontaneously intermittent transition between stable and thermo-acoustically unstable conditions. Three regimes, corresponding to stable, transitional and thermo-acoustically unstable were considered. High-speed OH^⁎ chemiluminescence (CL) imaging and planar particle image velocimetry (PIV) measurements revealed that the transition process was associated with periodic interactions between vortices and inner shear layers (ISLs), leading to large-scale back and forth propagation and reaction intensity fluctuations of the flame. Proper Orthogonal Decomposition (POD) analysis indicated that the transition featured the presence of precessing vortex core (PVC), which contributed to the helical motion of the flame. Additionally, it was also shown that the flame appeared in outer recirculation (ORZ) zone most frequently during stable state as compared to both transitional and unstable cases. Such phenomenon further suggested that the flame in the ORZ could only serve as a necessary but insufficient condition for the transition from stable to thermo-acoustically unstable states, depending on the geometry and thermal state of the combustor.