Locking of azimuthal modes by breaking the symmetry in annular combustors

Aguilar, José G.; Dawson, James; Schuller, Thierry; Durox, Daniel; Prieur, Kevin; Candel, Sébastien

doi:10.1016/j.combustflame.2021.111639

Cited by 20 publications

(13 citation statements)

References 27 publications

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“…These observations are manifestations of explicit rotational symmetry breaking in spite of the fact that these combustors were designed to be rotationally symmetric, in contrast to the studies of Dawson & Worth (2013) and Aguilar et al. (2021) where the symmetry is deliberately broken by using baffles or different types of burners. In this work, we will explain this hitherto unexplained phenomenon, elucidating why imperceptible system asymmetries have a highly detectable effect on the thermoacoustic dynamics in the vicinity of the Hopf bifurcation.…”

Section: Introductionmentioning

confidence: 84%

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Spontaneous and explicit symmetry breaking of thermoacoustic eigenmodes in imperfect annular geometries

et al. 2022

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This article deals with the symmetry breaking of azimuthal thermoacoustic modes in annular combustors. Using a nominally symmetric annular combustor, we present experimental evidence of a predicted spontaneous reflectional symmetry breaking, and also an unexpected explicit rotational symmetry breaking in the neighbourhood of the Hopf bifurcation which separates linearly stable azimuthal thermoacoustic modes from self-oscillating modes. We derive and solve a multidimensional Fokker–Planck equation to unravel a unified picture of the phase space topology. We demonstrate that symmetric probability density functions of the thermoacoustic state vector are elusive, because the effect of asymmetries, even imperceptible ones, is magnified close to the bifurcation. This conclusion implies that the thermoacoustic oscillations of azimuthal modes in real combustors will systematically exhibit a statistically dominant orientation of the mode in the vicinity of the Hopf bifurcation.

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Section: Introductionmentioning

confidence: 84%

“…Dawson & Worth (2013) and Aguilar et al. (2021) investigated this type of symmetry breaking by means of various rotationally asymmetric annular configurations, and Noiray et al. (2011) showed that rotational resistive acoustic asymmetries cause this type of symmetry breaking of the thermoacoustic dynamics.…”

Section: Introductionmentioning

confidence: 99%

Spontaneous and explicit symmetry breaking of thermoacoustic eigenmodes in imperfect annular geometries

et al. 2022

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“…These azimuthal modes, in turn, induce axial velocity fluctuations in each injector [4], a process that dominantly leads to heat release rate fluctuations. Experiments carried out on lab-scale and industrial annular combustors [5][6][7][8], numerical simulations [4,[9][10][11][12], and theoretical analysis [13,14] have provided a wealth of information on azimuthal coupling. Other investigations aim to develop active and passive control techniques [15][16][17][18] to reduce such instabilities.…”

Section: Introductionmentioning

confidence: 99%

“…Rajendram Soundararajan et al, GTP-22-1357, Copyright © 2022 by ASME pure azimuthal modes, such as standing, spinning [22], and slanted [23] modes, were observed in this system. Experiments were also carried out on this combustor to identify the effect of symmetry breaking by partially blocking the injectors or changing their geometry [8].…”

Section: Introductionmentioning

confidence: 99%

Azimuthal Instabilities of an Annular Combustor With Different Swirling Injectors

Soundararajan

Durox

Renaud

et al. 2022

Journal of Engineering for Gas Turbines and Power

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Experiments are carried out on a laboratory-scale annular combustor with liquid heptane to examine the effects of swirlers on azimuthal instabilities. Five types of swirlers varying in swirl numbers and pressure drops are considered. These swirlers can be broadly categorized into two groups, lower-swirl, and higher-swirl groups, based on their swirl numbers. Results reveal that none of the swirlers in the lower-swirl category exhibit instability in the operating region considered, whereas the higher-swirl units feature strong azimuthal instabilities. Among the higher-swirl group, a higher pressure drop swirler is associated with a broader instability map. This shows that the transition to instability mainly depends on the swirl number through its effect on flame structure and pressure drop adds to further variations. An attempt is made to interpret the occurrence of instabilities by making use of flame describing functions (FDFs) measured in a single-injector combustor. The observed instability behavior is tentatively interpreted using an instability analysis in which the injector and upstream plenum are represented by an impedance that shifts the instability band. The unstable behavior is then linked to the relative position of the FDF phase with respect to the instability band in the expected azimuthal mode frequency range. The phase and gain of the FDF notably depend on the swirl number, and it is possible to distinguish, for the present configuration, a category of low swirl number injectors inducing stable operation and another category of high swirl number units leading to oscillations.

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“…Bauerheim, Cazalens & Poinsot 2015; Ghirardo, Juniper & Moeck 2016; Rouwenhorst, Hermann & Polifke 2017; Aguilar et al. 2021; Faure-Beaulieu et al. 2021 a ).…”

Section: Introductionmentioning

confidence: 99%

Self-sustained azimuthal aeroacoustic modes. Part 1. Symmetry breaking of the mean flow by spinning waves

Faure-Beaulieu,

Xiong,

Pedergnana

et al. 2023

J. Fluid Mech.

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In this paper, we study the aeroacoustic instability which occurs in a deep axisymmetric cavity in a turbulent pipe flow. This phenomenon is the axisymmetric counterpart of the classical whistling of a rectangular deep cavity subject to a grazing flow. The whistling of such axisymmetric cavity originates from the interaction of the coherent fluctuations of the vorticity at the cavity's opening with one of its trapped azimuthal or radial acoustic modes. We focus here on the situation involving the first pure azimuthal mode, which is trapped in the cavity. As a consequence of the rotational symmetry of the configuration, azimuthal modes are actually pairs of degenerate eigenmodes, or almost degenerate in the presence of small asymmetries. Therefore, the aeroacoustic instabilities exhibit more complex mechanisms than in the case of a rectangular deep cavity. In particular, we show that self-sustained spinning modes induce a symmetry breaking of the mean flow and we will elucidate the details of this phenomenon. To that end, simultaneous acoustic and time-resolved stereoscopic particle image velocimetry (PIV) measurements are performed. They reveal that when large-amplitude aeroacoustic waves spin around the cavity, a quasi-steady mean flow starts whirling slowly in the opposite direction to the wave propagation. A linear perturbation analysis around an axisymmetric mean flow confirms the experimental observations: although the incoming pipe flow is not swirling, the hydrodynamic component of the aeroacoustic wave induces such whirling motion of the mean flow because of the forcing from the steady part of the coherent Reynolds stress tensor.

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Locking of azimuthal modes by breaking the symmetry in annular combustors

Cited by 20 publications

References 27 publications

Spontaneous and explicit symmetry breaking of thermoacoustic eigenmodes in imperfect annular geometries

Spontaneous and explicit symmetry breaking of thermoacoustic eigenmodes in imperfect annular geometries

Azimuthal Instabilities of an Annular Combustor With Different Swirling Injectors

Self-sustained azimuthal aeroacoustic modes. Part 1. Symmetry breaking of the mean flow by spinning waves

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