Impact of Swirl Fluctuations on the Flame Response of a Perfectly Premixed Swirl Burner

Komarek, Thomas; Polifke, Wolfgang

doi:10.1115/1.4000127

Cited by 214 publications

(127 citation statements)

References 16 publications

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“…Previous theoretical studies suggest that vortex shedding may be at the origin of ITA modes [3], while others mention a possible counter-reaction of the flame to its own production of acoustics [2]. This section shows that mode conversion [17,[37][38][39][40], i.e. the transformation of an acoustic wave into a convective wave is the mechanism that must be introduced into the analysis to understand the instability loop.…”

Section: Description Of Physical Phenomena Responsible For Ita Modesmentioning

confidence: 99%

DNS of Intrinsic ThermoAcoustic modes in laminar premixed flames

Courtine

Selle

Poinsot

2015

Combustion and Flame

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OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. , Emmert et al. 2015 suggest that thermoacoustic modes can appear in combustors with anechoic terminations, which have no acoustic eigenmodes. These modes, called here Intrinsic ThermoAcoustic (ITA), can be predicted with simple theoretical arguments, but have been ignored for a long time. They are reproduced in this paper using Direct Numerical Simulation (DNS) of a laminar premixed Bunsen type flame. DNS results and theory are compared showing very good agreement in terms of both frequency and mode structure. DNS confirms that the frequency of ITA modes does not depend on any acoustic characteristic of the burner. Based on a numerical evaluation of the Flame Transfer Function, stability limits of ITA modes predicted by theory are also recovered in the DNS with reasonable accuracy. Finally, DNS is used to analyze the mechanisms of ITA modes.

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Section: Description Of Physical Phenomena Responsible For Ita Modesmentioning

confidence: 99%

DNS of Intrinsic ThermoAcoustic modes in laminar premixed flames

Courtine

Selle

Poinsot

2015

Combustion and Flame

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“…LES is well suited to unsteady combustion and is a useful tool to predict thermoacoustic limit cycles or FTFs [17,32,20]. The LES solver is described in Section 3.1, and the mesh and boundary conditions are given in Sections 3.2 and 3.3, respectively.…”

Section: Large Eddy Simulationmentioning

confidence: 99%

“…It is affected by different mechanisms acting simultaneously on the heat release rate fluctuation and therefore difficult to separate [25]: the axial velocity perturbation [26][27][28][29], the perturbation of swirl [30][31][32][33][34] and the perturbation of mixing [35][36][37][38]. The gain of FTFs for swirled flames exhibits a typical shape: it starts at 1, then increases towards a maximum, decreases to a local minimum at low frequencies, often reaches a second maximum at higher frequencies and decreases finally to low values at high frequencies.…”

Section: Introductionmentioning

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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“…In particular, the time lag need not be small, such that larger, more realistic values of τ can be chosen. Furthermore, a spread in time lags, as it is often observed in flame transfer functions [29,30] can also be considered. Results for such cases will be presented in the next section.…”

Section: A State-space Model For the N-thermoacoustic Systemmentioning

confidence: 99%

A Discrete-Time, State-Space Approach for the Investigation of Non-Normal Effects in Thermoacoustic Systems

Mangesius

Polifke

2011

International Journal of Spray and Combustion Dynamics

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A low-order, state-space modeling approach for thermoacoustic systems has been developed, which is based on present and past values of nodal characteristic wave amplitudes. The method allows to simulate the time evolution of the system state, but also the efficient computation of the (pseudo-)spectrum of the evolution operator. It is demonstrated by comparison with a frequencydomain "network model" that eigenmodes and asymptotic linear stability are predicted correctly. The influence of various model parameters (downstream reflection coefficient, temperature ratio across the heat source, magnitude and spread of heat source time delays) on transient growth of perturbation energy is explored. The discussion in the present paper is limited to simple test cases, but the approach can be generalized to systems with non-trivial topology.

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Impact of Swirl Fluctuations on the Flame Response of a Perfectly Premixed Swirl Burner

Cited by 214 publications

References 16 publications

DNS of Intrinsic ThermoAcoustic modes in laminar premixed flames

DNS of Intrinsic ThermoAcoustic modes in laminar premixed flames

Bistable swirled flames and influence on flame transfer functions

A Discrete-Time, State-Space Approach for the Investigation of Non-Normal Effects in Thermoacoustic Systems

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