Impacts of Multi-Swirl Interaction Pattern on Self-Excited Instability Combustion Characteristics

Experimental and numerical investigations have been carried out on the effects of multi-swirl interaction patterns on self-excited unstable combustion characteristics based on a five-nozzle can combustor. The multi-swirl interaction patterns include equal swirl intensity interaction and strong-weak swirl interaction. The thermo-acoustic instability characteristics indicate that increasing the central nozzle swirl intensity transforms the interaction pattern from equal swirl intensity interaction to strong-weak swirl interaction, which can significantly weaken the thermo-acoustic coupling effect under low equivalence ratio conditions, and substantially reduce the dynamic pressure amplitude during unstable combustion. The instantaneous flame structures show that the multi-swirl flames exhibit chaotic oscillations under low equivalence ratio conditions. With equivalence ratios greater than 0.71, a clear flame interaction boundary appears, and the flames can exhibit periodic oscillations in a regular structure. However, different interaction patterns result in the completely different phase oscillations in the central and outer flames. The time-averaged flame structures also indicate that strong-weak swirl interaction leads to an increase in the flame angle and a decrease in the flame length for both the central and outer flames, and the variations in the flame angle and length have great impacts on the thermo-acoustic instability mode. The fuel-staging combustion characteristics demonstrate that the instability combustion conditions with a dominant frequency of 100 Hz are greatly broadened by the strong-weak swirl interaction pattern, and the overlapping operating conditions between this mode and other modes are greatly increased. This implies that it is more flexible to adjust the thermo-acoustic unstable mode, which is conducive to the passive suppression of thermo-acoustic instability.