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This experimental study investigates the dynamical transition from stableoperation to thermoacoustic instability in a turbulent bluff-body stabilizeddump combustor. We conduct experiments to characterize the dynamical transitionutilizing acoustic pressure and local heat release rate fluctuations. Weobserve the transition to thermoacoustic instability for these experiments aswe decrease the equivalence ratio towards a fuel-lean setting. Moreimportantly, we observe significant growth of local heat release ratefluctuations near the bluff-body well before the appearance of large-scalespatial or temporal patterns during the occurrence of thermoacousticinstability. By strategically positioning slots (perforations) on thebluff-body, we ensure the reduction of the growth of local heat release ratefluctuations at the stagnation zone near the bluff-body at operating conditionsfar away from the onset of thermoacoustic instability. This reduction in thelocal heat release rate fluctuations ensures that the transition tothermoacoustic instability is avoided. We find that modified configurations ofthe bluff-body that do not quench these local heat release rate fluctuations atthe stagnation zone results in the transition to thermoacoustic instability. Wealso reveal that an effective suppression strategy based on the growth of localheat release rate fluctuations requires an optimization of the area ratio ofthe slots for a given bluff-body position. Further, the suppression strategyalso depends on the spatial distribution of perforations on the bluff-body.Notably, an inappropriate distribution of the slots which does not quench thelocal heat release rate fluctuations at the stagnation zone may even result ina dramatic increase in amplitudes of pressure oscillations.

Control of growth of local heat release rate fluctuations to suppress thermoacoustic instability