Effect of flame response asymmetries on the modal patterns and collective states of a can-annular lean-premixed combustion system

We experimentally study the effect of rotational asymmetries in the flame response distribution on the ther-moacoustic oscillations of four turbulent lean-premixed combustors coupled in a ring network. The asym-metries are created via different combinations of high-swirl (HS) and low-swirl (LS) nozzles. By analyzing the inter-combustor acoustic interactions in terms of discrete thermoacoustic modes, we find a variety of modal patterns: (i) global alternating push-pull modes emerge for most pair-wise asymmetric nozzle combinations, (ii) 2-can push-pull modes emerge for an alternating 2-fold symmetric nozzle combination, and (iii) strong mode localization and global push-push modes emerge when the HS nozzles outnumber the LS nozzles. Us-ing a complex systems framework, we reinterpret these modal patterns as collective states, such as a weak breathing chimera, a weak anti-phase chimera, and in-phase/anti-phase synchronization. This study shows that changing the flame response distribution of a multi-combustor system, via changes in the nozzle swirl distribution, can induce a variety of modal patterns and collective states. This sets the stage for the potential use of rotational asymmetries in the passive control of thermoacoustic modes in can-annular combustion systems.& COPY; 2022 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

We experimentally studied the effect of rotational asymmetries in flame response distribution on thermoacoustic oscillations in a network of four combustors. Different nozzle combinations were used to create the asymmetries. By analyzing the acoustic interactions between combustors, we observed various modal patterns and collective states. This study demonstrates the potential use of rotational asymmetries for passive control of thermoacoustic modes in combustion systems.