Experimental study on flame/flow dynamics in a multi-nozzle gas turbine model combustor under thermo-acoustically unstable condition with different swirler configurations

Abstract

This paper presents an experimental study on the combustion stability characteristics and flame/flow dynamics in a multi-nozzle, lean premixed prevaporized (LPP), swirl-stabilized gas turbine model combustor with different swirler configurations in the presence of self-excited combustion instability. The flame structure was characterized using high-speed OH⁎ chemiluminescence imaging and the flow field across the centerline of three interacting flames was measured by high-speed planar Particle Image Velocimetry (PIV). Two sets of the swirler configurations were considered in this paper, featuring different combinations of swirl rotational directions. The first one consisted of three co-rotating swirlers, whereas the central swirler in the second configuration was replaced by a swirler with counter-rotation direction. These two configurations were termed as COS and CNS combustors respectively in the rest of the paper. It was found that these two combustors exhibited similar stable and unstable operating domains in terms of different equivalence ratios and inlet air velocities. At the same test condition, the amplitude of dominant instability of COS combustor was 130 dB, which was stronger than that of CNS combustor (120 dB). Phase-averaged PIV measurements showed that both COS and CNS combustor featured three recirculation zones downstream the swirlers, and high axial velocity was present after the merging of the adjacent flames. These two flow structures varied periodically, but in different manners for COS and CNS combustors. Phase-averaged OH⁎ chemiluminescence images indicated that the flame was primarily anchored in recirculation zones close to the swirler and most of the heat release was found to occur in flame interaction regions, where large-scale reaction intensity variations occurred. Furthermore, a greater phase delay between heat release rate and acoustic pressure was observed in CNS combustor, which contributed to a weaker instability comparing with that in the COS combustor.