Self-induced instabilities of premixed flames in a multiple injection configuration

Noiray, Nicolas; Durox, Daniel; Schuller, Thierry; Candel, Sébastien

doi:10.1016/j.combustflame.2006.01.006

Cited by 73 publications

(55 citation statements)

References 26 publications

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“…They are due to a resonant coupling of the unsteady heat release and the acoustics propagating in the system and their prediction has become an important task to prevent their appearance at an early design stage [18][19][20]. For acoustically compact flames the linear analysis of combustion instabilities is generally performed with the Flame Transfer Function (FTF) introduced by Crocco [21,22] and more recently with the Flame Describing Function (FDF) [23,24]. In these approaches the FTF is defined as the relative heat release fluctuation ðq=qÞ to the relative inlet velocity perturbation ðû=uÞ induced by the acoustic field:…”

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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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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“…If the flame TF is measured inside the burner deck or close above the slit outlet then the relation between the local velocity and acoustic velocity in a plane wave in the burner upstream part should be incorporated. In [13,30] (Fig. 4), slit width (Fig.…”

Section: Discussionmentioning

confidence: 98%

“…The cause of the amplification of the response over its quasi-steady value lies in the interference between perturbations which originate from the anchoring point and travel along the flame, and a convective perturbation of the flow pattern [29]. A TF gain above 1 was also measured for multiple flame burner heads [15,30]. At the same time, both the theoretical and the experimental TF of a single conical flame shows a TF gain less than 1 for the whole frequency range.…”

Section: The Genesis Of Thermo-acoustic Models Of Premixed Bunsen-typmentioning

confidence: 99%

Experimental and Numerical Investigation of the Acoustic Response of Multi-slit Bunsen Burners

Kornilov¹,

Rook²,

Boonkkamp³

et al. 2008

Proceedings of Meetings on Acoustics

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“…First of all, let us restrict the dataset to compare the instability of only one frequency (or mode) per parameter setting, as is regularly done in literature, e.g. [10]. This means that in case multiple frequency components, or modes, are present in either the simulated or experimental datasets, one should select only one pair for the comparison and further quality assessment.…”

Section: Model Quality Assessmentmentioning

confidence: 99%

“…In [10,11] for example, (in) stability experiments on a laboratory combustor were compared to a linear, and later a nonlinear model [9] by varying the length of the upstream duct. In all mentioned literature however [9][10][11], the model quality was inferred from comparing the visual discrepancy of the predictions versus the experimental points. Although such an approach gives a reasonable qualitative indication it remains difficult to answer important quantitative questions such as:' What is the likelihood a stable prediction will be correct?…”

Section: Introductionmentioning

confidence: 99%

Accuracy Assessment of Thermoacoustic Instability Models Using Binary Classification

Hoeijmakers

Arteaga

Kornilov

et al. 2013

International Journal of Spray and Combustion Dynamics

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We apply binary classification theory to assess the (in)stability prediction accuracy of thermoacoustic models. It is shown that by applying such methods to compare a large set of stability predictions and experiments it is possible to gain valuable qualitative insight in different aspects of prediction quality. The approach is illustrated with a 2-port model and a large experimental data set. The presented framework provides an unified and practical tool to answer questions such as (i) What is the chance that a stable prediction will be correct? and (ii) How conservative is the model? It is shown that the most suitable quality indicator is strongly dependent on the actual purpose of the model. The method provides a solid starting point for model comparison and optimization.

show abstract

Self-induced instabilities of premixed flames in a multiple injection configuration

Cited by 73 publications

References 26 publications

Bistable swirled flames and influence on flame transfer functions

Bistable swirled flames and influence on flame transfer functions

Experimental and Numerical Investigation of the Acoustic Response of Multi-slit Bunsen Burners

Accuracy Assessment of Thermoacoustic Instability Models Using Binary Classification

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