Header menu link for other important links
X
Onset of thermoacoustic instability in turbulent combustors: An emergence of synchronized periodicity through formation of chimera-like states
Published in Cambridge University Press
2017
Volume: 811
   
Pages: 659 - 681
Abstract
Thermoacoustic systems with a turbulent reactive flow, prevalent in the fields of power and propulsion, are highly susceptible to oscillatory instabilities. Recent studies showed that such systems transition from combustion noise to thermoacoustic instability through a dynamical state known as intermittency, where bursts of large-amplitude periodic oscillations appear in a near-random fashion in between regions of low-amplitude aperiodic fluctuations. However, as these analyses were in the temporal domain, this transition remains still unexplored spatiotemporally. Here, we present the spatiotemporal dynamics during the transition from combustion noise to limit cycle oscillations in a turbulent bluff-body stabilized combustor. To that end, we acquire the pressure oscillations and the field of heat release rate oscillations through high-speed chemiluminescence images of the reaction zone. With a view to get an insight into this complex dynamics, we compute the instantaneous phases between acoustic pressure and local heat release rate oscillations. We observe that the aperiodic oscillations during combustion noise are phase asynchronous, while the large-amplitude periodic oscillations seen during thermoacoustic instability are phase synchronous. We find something interesting during intermittency: patches of synchronized periodic oscillations and desynchronized aperiodic oscillations coexist in the reaction zone. In other words, the emergence of order from disorder happens through a dynamical state wherein regions of order and disorder coexist, resembling a chimera state. Generally, mutually coupled chaotic oscillators synchronize but retain their dynamical nature; the same is true for coupled periodic oscillators. In contrast, during intermittency, we find that patches of desynchronized aperiodic oscillations turn into patches of synchronized periodic oscillations and vice versa. Therefore, the dynamics of local heat release rate oscillations change from aperiodic to periodic as they synchronize intermittently. The temporal variations in global synchrony, estimated through the Kuramoto order parameter, echoes the breathing nature of a chimera state. © 2016 Cambridge University Press.
About the journal
JournalData powered by TypesetJournal of Fluid Mechanics
PublisherData powered by TypesetCambridge University Press
ISSN00221120
Open AccessNo
Concepts (26)
  •  related image
    Acoustic noise
  •  related image
    CHEMILUMINESCENCE
  •  related image
    Circuit oscillations
  •  related image
    Combustion
  •  related image
    Dynamical systems
  •  related image
    Dynamics
  •  related image
    Nonlinear dynamical systems
  •  related image
    Oscillators (electronic)
  •  related image
    Oscillators (mechanical)
  •  related image
    Stability
  •  related image
    Synchronization
  •  related image
    Thermoacoustics
  •  related image
    COUPLED CHAOTIC OSCILLATORS
  •  related image
    Heat release rate (hrr)
  •  related image
    Limit cycle oscillation (lco)
  •  related image
    Nonlinear instability
  •  related image
    OSCILLATORY INSTABILITY
  •  related image
    SPATIO-TEMPORAL DYNAMICS
  •  related image
    Thermoacoustic instability
  •  related image
    Turbulent reacting flows
  •  related image
    Combustors
  •  related image
    Instability
  •  related image
    Periodicity
  •  related image
    Spatial variation
  •  related image
    Temporal variation
  •  related image
    Turbulent flow