Seeds of phase transition to thermoacoustic instability

Abstract

Tackling the problem of emissions is at the forefront of scientific research today. While industrial engines designed to operate in stable regimes produce emissions, attempts to operate them at "greener" conditions often fail due to thermoacoustic instability. During thermoacoustic instability, hazardous high amplitude periodic oscillations lead to failure of these engines in power plants, aircrafts and rockets. Yet, identifying the onset of thermoacoustic instability remains elusive due to spatial variability and the continuous evolution of spatiotemporal patterns in the reacting flow field. Here, we show experimental evidence of early manifestation of the onset of thermoacoustic instability at certain zones. Our findings allow us to identify a critical threshold that enables us to distinguish stable operating regimes from hazardous operations. This opens new perspectives for predicting the onset of thermoacoustic instability and could be a step forward to "greener" operations. The developed methodology is applicable for other systems exhibiting phase transitions.

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

“…First, we analyze the results obtained for experiments with a combustor length of 1100 mm, operating at ṁfuel of 34 SLPM with the bluff-body positioned 45 mm from the dump plane and where ṁair changes at a rate of 3 SLPM/s. We name this set of operating conditions and experimental configurations used in [15] as the reference experimental configuration (REC) for the purpose of comparing the results. For all the subsequent figures, instead of discussing the plots with respect to ṁair , we describe the figures using the global equivalence ratio φ.…”

“…Recently, in a bluff-body stabilized dump turbulent combustor, Raghunathan et al [15] showed early local growth of flame fluctuations prior to the onset of thermoacoustic instability. In particular, they revealed significant growth of local heat release rate fluctuations occurring at certain zones within the combustor, located around the bluff-body.…”

“…In the present study, we target one of these interconnected zones. We perform experiments with modified designs of the bluff-body to reduce the growth of local heat release rate fluctuations at a critical location revealed in [15], namely the stagnation zone upstream of the bluff-body. Reducing the growth of local heat release rate fluctuations at the stagnation zone results in the suppression of the transition to thermoacoustic instability.…”