A reduced-order model for the onset of combustion instability: Physical mechanisms for intermittency and precursors

Nair, Vineeth; Sujith, R. I.

doi:10.1016/j.proci.2014.07.007

Cited by 84 publications

(34 citation statements)

References 23 publications

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“…A simple phenomenological model for combustion instability in a bluff-body-stabilized combustor was developed by Nair & Sujith (2014) by incorporating both the broad-band effects of turbulence and the narrow-band effects of vortex formation and impingement into the classical Galerkin-based acoustic analysis. The model reproduces the intermittency route to instability as the flow velocity is increased and exhibits instability when the hydrodynamic forcing is at the subharmonic frequency of the fundamental acoustic mode.…”

Section: Intermittency In Turbulent Combustorsmentioning

confidence: 99%

Intermittency route to thermoacoustic instability in turbulent combustors

2014

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The dynamic transition from combustion noise to combustion instability was investigated experimentally in two laboratory-scale turbulent combustors (namely, swirl-stabilized and bluff-body-stabilized backward-facing-step combustors) by systematically varying the flow Reynolds number. We observe that the onset of combustion-driven oscillations is always presaged by intermittent bursts of highamplitude periodic oscillations that appear in a near-random fashion amidst regions of aperiodic low-amplitude fluctuations. These excursions to periodic oscillations last longer in time as operating conditions approach instability and finally the system transitions completely into periodic oscillations. A continuous measure to quantify this bifurcation in dynamics can be obtained by defining an order parameter as the probability of the signal amplitude exceeding a predefined threshold. A hysteresis zone was observed in the bluff-body-stabilized configuration that was absent in the swirlstabilized configuration. The recurrence properties of the dynamics of intermittent burst oscillations were quantified using recurrence plots and the distribution of the aperiodic phases was examined. From the statistics of these aperiodic phases, robust early-warning signals of an impending combustion instability may be obtained.

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Section: Intermittency In Turbulent Combustorsmentioning

confidence: 99%

Intermittency route to thermoacoustic instability in turbulent combustors

2014

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“…when an eigenvalue becomes unstable, and subcritical bifurcations, i.e., when eigenvalues are stable but the nonlinearity is triggered by finite-amplitude perturbations . When the bifurcation F. Huhn and L. Magri parameter is varied, thermoacoustic systems may display periodic, quasi-periodic and chaotic oscillations (Kabiraj et al 2011;Gotoda et al 2011Gotoda et al , 2012Kabiraj et al 2012;Kashinath et al 2014;Waugh et al 2014;Nair et al 2014;Nair & Sujith 2015;Orchini et al 2015). Whereas methods to investigate the stability and sensitivity of fixed points and periodic solutions are well established (e.g.…”

Section: Introductionmentioning

confidence: 99%

Stability, sensitivity and optimisation of chaotic acoustic oscillations

Huhn

Magri

2019

J. Fluid Mech.

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In an acoustic cavity with a heat source, such as a flame in a gas turbine, the thermal energy of the heat source can be converted into acoustic energy, which may generate a loud oscillation. If uncontrolled, these nonlinear acoustic oscillations, also known as thermoacoustic instabilities, can cause large vibrations up to structural failure. Numerical and experimental studies showed that thermoacoustic oscillations can be chaotic. It is not yet known, however, how to minimise such chaotic oscillations. We propose a strategy to analyse and minimise chaotic acoustic oscillations, for which traditional stability and sensitivity methods break down. We investigate the acoustics of a nonlinear heat source in an acoustic resonator. First, we propose covariant Lyapunov analysis as a tool to calculate the stability of chaotic acoustics making connections with eigenvalue and Floquet analyses. We show that covariant Lyapunov analysis is the most general flow stability tool. Second, covariant Lyapunov vector analysis is applied to a chaotic system. The time-averaged acoustic energy is investigated by varying the heat-source parameters. Thermoacoustic systems can display both hyperbolic and non-hyperbolic chaos, as well as discontinuities in the time-averaged acoustic energy. Third, we embed sensitivities of the time-averaged acoustic energy in an optimisation routine. This procedure achieves a significant reduction in acoustic energy and identifies the bifurcations to chaos.The analysis and methods proposed enable the reduction of chaotic oscillations in thermoacoustic systems by optimal passive control. The techniques presented can be used in other unsteady fluid dynamics problems with virtually no modification.

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“…[23][24][25][26][27]. These studies on self-excited nonlinear thermoacoustic oscillations show that thermoacoustic systems can exhibit quite a rich variety of nonlinear behavior.…”

Section: Introductionmentioning

confidence: 99%

Chaos in an imperfectly premixed model combustor

Kabiraj

Saurabh

Karimi

et al. 2015

Chaos: An Interdisciplinary Journal of Nonlinear Science

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This article reports nonlinear bifurcations observed in a laboratory scale, turbulent combustor operating under imperfectly premixed mode with global equivalence ratio as the control parameter. The results indicate that the dynamics of thermoacoustic instability correspond to quasi-periodic bifurcation to low-dimensional, deterministic chaos, a route that is common to a variety of dissipative nonlinear systems. The results support the recent identification of bifurcation scenarios in a laminar premixed flame combustor (Kabiraj et al., Chaos: Interdiscip. J. Nonlinear Sci. 22, 023129 (2012)) and extend the observation to a practically relevant combustor configuration.

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A reduced-order model for the onset of combustion instability: Physical mechanisms for intermittency and precursors

Cited by 84 publications

References 23 publications

Intermittency route to thermoacoustic instability in turbulent combustors

Intermittency route to thermoacoustic instability in turbulent combustors

Stability, sensitivity and optimisation of chaotic acoustic oscillations

Chaos in an imperfectly premixed model combustor

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