Modeling transition to thermoacoustic instability in a turbulent combustor: A synchronization-based approach

Thermoacoustic instability, arising from interactions between the fluctuations in heat release and pressure, limits the stable operation of gas turbines in fuel-lean conditions. Modeling the dynamics of such instability in a modern gas turbine combustor, where combustion occurs in a turbulent environment, becomes key for safe and reliable operations. This work presents a phenomenological reduced-order model based on synchronization for the transition to thermoacoustic instability in such turbulent combustors. Here, the acoustic field and the unsteady heat release rate from the turbulent reactive flow are modeled as two non-linearly coupled sub-systems. By varying the coupling strength, the model can replicate the transition from low amplitude chaotic oscillation (i. e. combustion noise) to high amplitude periodic oscillation through intermittency, which is observed in previous experiments. The model shows that the pressure fluctuation in the regime of combustion noise is multifractal at one end of the transition. During the transition to the limit cycle oscillation, the pressure fluctuation loses its multifractality and poses a higher amplitude, which is the hallmark of the transition mechanism in turbulent thermoacoustic systems shown by previous experiments.