A Tool to Study Azimuthal Standing and Spinning Modes in Annular Combustors

Sensiau, Claude; Nicoud, Franck; Poinsot, Thiérry

doi:10.1260/147547209786235037

Cited by 31 publications

(31 citation statements)

References 11 publications

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“…A double Hopf bifurcation occurs at β = α, where two complex eigenvalues cross the imaginary axis at the same time. Similarly, Sensiau et al [12] perform a linear stability analysis of an azimuthally symmetric chamber and find two linearly unstable spinning modes with exactly the same growth rate. They conclude that, in perfectly symmetric systems, the sum of the two identical spinning modes would lead to a stable standing mode.…”

Section: Stability Of the Coupled Oscillator Systemmentioning

confidence: 93%

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Azimuthal instabilities in annular combustors: standing and spinning modes

2013

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This theoretical study investigates spinning and standing modes in azimuthally symmetric annular combustion chambers. Both modes are observed in experiments and simulations, and an existing model predicts that spinning modes are the only stable state of the system. We extend this model to take into account the effect that the acoustic azimuthal velocity, u, has on the flames, and propose a phenomenological model based on experiments performed on transversely forced flames. This model contains a parameter, δ, that quantifies the influence that the transversal excitation has on the fluctuating heat release. For small values of δ, spinning modes are the only stable state of the system. In an intermediate range of δ, both spinning and standing modes are stable states. For large values of δ, standing modes are the only stable state. This study shows that a flame's response to azimuthal velocity fluctuations plays an important role in determining the type of thermoacoustic oscillations found in annular combustors.

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Section: Stability Of the Coupled Oscillator Systemmentioning

confidence: 93%

“…Spatial averaging has already been applied, and the effects of a non-uniform speed of sound have been neglected [11]. This is common to many other studies modelling this problem [7,12]. Terms of order O(ū) are neglected by assuming a low Mach number flow.…”

Section: Introductionmentioning

confidence: 99%

Azimuthal instabilities in annular combustors: standing and spinning modes

2013

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“…3). The use of a single sector LES instead of a full annular LES is justified by the ISAAC assumption assuming that azimuthal modes mainly induce longitudinal fluctuations in each burner and can thus be studied on a single sector [44,45].…”

Section: Target Configurationmentioning

confidence: 99%

Bistable swirled flames and influence on flame transfer functions

Hermeth

Staffelbach

Gicquel

et al. 2014

Combustion and Flame

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Large Eddy Simulations (LES) are used to study a lean swirl-stabilized gas turbine burner where the flow exhibits two stable states. In the first one, the flame is attached to the central bluff body upstream of the central recirculation zone which contains burnt gases. In the second one the flame is detached from the central bluff body downecirculation zone which is filled by cold unburnt gases and dominated by a strong Precessing Vortex Core (PVC). The existence of these two states has an important effect on the dynamic response of the flame (FTF): both gain and phase of the FTF change significantly in the detached case compared to the attached one, suggesting that the stability of the machine to thermoacoustic oscillations will differ, depending on the flame state. Bifurcation diagrams show that the detached flame cannot be brought back to an attached position with an increased fuel flow rate, but it can be re-attached by forcing it at high amplitudes. The attached flame however, behaves inversely: it can be brought back to the detached position by both decreasing or increasing the pilot mass flow rate, but it remains attached at all forcing amplitudes. IntroductionSwirling flows are commonly used to help flame stabilization in gas turbine combustion chambers. They feature several types of vortex breakdown and can exhibit bifurcation phenomena where different states can co-exist and the flow can jump spontaneously from one to another [1,2]. Bifurcations of flames in configurations which are close to real gas turbine chambers have not been investigated so far even though engineers report that they observe these mechanisms and that there is a link between flame states and thermoacoustic instabilities: when the flame changes from one state to another, its acoustic stability characteristics also change.Two dynamic phenomena are usually observed in swirled combustion chambers: (1) a helical flow instability, the so-called precessing vortex core (PVC) and (2) thermo-acoustic instabilites.The PVC is an hydrodynamic instability in swirling flows [3].I t is a large scale structure characterized by a regular rotation of a spiral structure around the geometrical axis of the combustion chamber. It can occur at high Reynolds and swirl number flows [4][5][6][7][8][9][10] and its precession frequency is controlled by the rotation rate of the swirled flow [3]. Several studies show that combustion can suppress the PVC [6,7,11], but other cases also show PVCs which are present in reacting flows [12][13][14][15]. The interaction of PVC with flames has been analyzed for example by Stöhr et al.[16]: they found the PVC to enhance mixing and to increase the flame surface. This was associated to structures in the inner shear layer, whereas Moeck et al. [15] observed the outer shear layer to create most of the flame perturbations. Both researchers as well as Staffelbach [13] using LES evidenced a ''finger-like'' rotating structure at the flame foot around which the PVC is turning. Furthermore, asymmetric fluctuations of the he...

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“…Experiments have also been developed [8,9], confirming LES results but also raising additional questions, for example linked to the effect of outlet conditions on the development of modes. Various theories have been proposed [5,[10][11][12][13], focusing on two questions: (1) what controls the nature and the occurrence of azimuthal modes? and (2) is it possible to suppress them?…”

Section: Introductionmentioning

confidence: 99%

A theoretical study of mean azimuthal flow and asymmetry effects on thermo-acoustic modes in annular combustors

Bauerheim

Cazalens

Poinsot

2015

Proceedings of the Combustion Institute

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To cite this version:Michaël Bauerheim, Michel Cazalens, Thierry Poinsot. A theoretical study of mean azimuthal flow and asymmetry effects on thermo-acoustic modes in annular combustors. Proceedings of the Combustion Institute, Elsevier, 2015, vol. 35 (n°3) AbstractThe objective of this paper is to develop an analytical model to capture two symmetry breaking effects controlling the frequency and nature (spinning, standing or mixed) of azimuthal modes appearing in annular chambers: (1) Using two different burner types distributed along the chamber (2) Considering the mean azimuthal flow due to the swirlers or to effusion cooling. The ATACAMAC (Analytical Tool to Analyze and Control Azimuthal Modes in Annular Chambers) methodology is applied using the linearized acoustic equations with a steady and uniform azimuthal mean flow. It provides an analytical implicit dispersion relation which can be solved numerically. A fully analytical resolution is possible when the annular chamber is weakly coupled to the burners. Results show that symmetry breaking, either by mixing burners types or with a mean azimuthal flow, splits the azimuthal modes into two waves with different frequencies and structures. Breaking symmetry promotes standing modes but adding even a low azimuthal mean flow fosters spinning modes so that the azimuthal mean flow must be taken into account to study azimuthal modes.

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A Tool to Study Azimuthal Standing and Spinning Modes in Annular Combustors

Cited by 31 publications

References 11 publications

Azimuthal instabilities in annular combustors: standing and spinning modes

Azimuthal instabilities in annular combustors: standing and spinning modes

Bistable swirled flames and influence on flame transfer functions

A theoretical study of mean azimuthal flow and asymmetry effects on thermo-acoustic modes in annular combustors

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