Self-coupled turbulent combustor

Synopsis

Bouyed by our success in suppressing thermoacoustic instability in a laminar horizontal Rijke tube via self-coupling, we decided to test the idea on a complex system: turbulent bluff body stabilized combustor (TARA - ThermoAcoustic Rig for Axial instabilities). We report a complete suppression of oscillations (acoustic pressure amplitude value during the suppressed state close to the value observed during the state of combustion noise) when the combustor is acoustically self-coupled with optimal coupling parameters..

Self-coupling is achieved by coupling the acoustic field of the combustor to itself through a coupling tube. We characterize the effects of such acoustic self-feedback on the thermoacoustic instability of the system by varying the length and diameter of the coupling tube. We observe that the amplitude and the dominant frequency of the acoustic pressure fluctuations gradually decrease as the length of the coupling tube is increased. A complete suppression of thermoacoustic instability is observed when the coupling tube length is nearly 1.5 times the combustor length. Meanwhile, as we approach the suppression of thermoacoustic instability, the dynamical behavior of acoustic pressure changes from the state of limit cycle oscillations to low amplitude aperiodic oscillations via intermittency.

As the combustor approaches the state of complete suppression, the temporal synchrony between the acoustic pressure and the global heat release rate signals changes from the state of synchronized periodicity to desynchronized aperiodicity through intermittent synchronization. From the spatiotemporal analysis of the combustor flow field, we find complete disruption of the coherent spatial structures of acoustic energy production observed during the state of thermoacoustic instability when the combustor is self-coupled with a tube of optimized size.

References

  • Ankit Sahay, Abhishek Kushwaha, Samadhan A. Pawar, Midhun P.R., Jayesh M. Dhadphale, and R. I. Sujith, Mitigation of limit cycle oscillations in a turbulent thermoacoustic system via delayed acoustic self-feedback, Chaos, 33, 043118 (2023)