Mitigation of limit cycle oscillations in a turbulent thermoacoustic system via delayed acoustic self-feedback

TL;DR

This paper demonstrates that delayed acoustic self-feedback can effectively suppress limit cycle oscillations and thermoacoustic instability in turbulent combustors by disrupting positive feedback loops, offering a practical control method.

Contribution

It introduces a novel feedback control technique using a coupling tube to achieve amplitude death of oscillations in a turbulent combustor.

Findings

Complete suppression of oscillations at specific tube length

Transition from limit cycle to chaotic oscillations near suppression point

Disruption of positive feedback loop reduces thermoacoustic instability

Abstract

We report the occurrence of amplitude death (AD) of limit cycle oscillations in a bluff body stabilized turbulent combustor through delayed acoustic self-feedback. Such feedback control is achieved by coupling the acoustic field of the combustor to itself through a single coupling tube attached near the anti-node position of the acoustic standing wave. We observe that the amplitude and dominant frequency of the limit cycle oscillations gradually decrease as the length of the coupling tube is increased. Complete suppression (AD) of these oscillations is observed when the length of the coupling tube is nearly 3/8 times the wavelength of the fundamental acoustic mode of the combustor. Meanwhile, as we approach this state of amplitude death, the dynamical behavior of acoustic pressure changes from the state of limit cycle oscillations to low-amplitude chaotic oscillations via intermittency. We also study the change in the nature of the coupling between the unsteady flame dynamics and the acoustic field as the length of the coupling tube is increased. We find that the temporal synchrony between these oscillations changes from the state of synchronized periodicity to desynchronized aperiodicity through intermittent synchronization. Furthermore, we reveal that the application of delayed acoustic self-feedback with optimum feedback parameters completely disrupts the positive feedback loop between hydrodynamic, acoustic, and heat release rate fluctuations present in the combustor during thermoacoustic instability, thus mitigating instability. We anticipate this method to be a viable and cost-effective option to mitigate thermoacoustic oscillations in turbulent combustion systems used in practical propulsion and power systems.