Influence of the Swirler Design on the Flame Transfer Function of Premixed Flames

Hirsch, Christoph; Fanaca, D.; Reddy, P. Bala Anki; Polifke, Wolfgang; Sattelmayer, Thomas

doi:10.1115/gt2005-68195

Cited by 51 publications

(27 citation statements)

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“…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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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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“…extends almost tangentially to the streamlines in the diverging flow field until the jet velocity has decayed enough to allow steeper angles of the turbulent flame front [26]. Consequently the flame angle α is slightly larger than the flow jet angle.…”

Section: Figurementioning

confidence: 99%

“…Flame length model: The flame length model is developed as a function of thermal load, air excess ratio ratio λ, mixture preheat temperature, combustor pressure and flame geometry. An earlier investigation [26] had shown that the mean convective time delays can be computed from a simplified heat release profile exiting from a typical swirl burner. A schematic of the simplified geometric flame length model is shown in Fig.…”

Section: Scaling Rulesmentioning

confidence: 99%

Determination and Scaling of Thermo Acoustic Characteristics of Premixed Flames

Alemela

Fanaca

Hirsch

et al. 2010

International Journal of Spray and Combustion Dynamics

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The paper investigates the determination and the scaling of thermo acoustical characteristics of lean premixed flames as used in gas turbine combustion systems. In the first part, alternative methods to characterize experimentally the flame dynamics are outlined and are compared on the example of a scaled model of an industrial gas turbine burner. Transfer matrix results from the most general direct method are contrasted with data obtained from the hybrid method, which is based on Rankine-Hugoniot relations and the experimental flame transfer function obtained from OH*-chemiluminescence measurements. Also the new network model based regression method is assessed, which is based on a n − τ − σ dynamic flame model. The results indicate very good consistency between the three techniques, providing a global check of the methods/tools used for analyzing the thermo acoustic mechanisms of flames. In the second part, scaling rules are developed that allow to calculate the dynamic flame characteristics at different operation points. Towards this a geometric flame length model is formulated. Together with the other operational data of the flame it provides the dynamic flame model parameters at these points. The comparison between the measured and modeled flame lengths as well as the n − τ − σ parameters shows an excellent agreement. NOMENCLATURE

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“…Straub and Richards [9] first noticed a strong impact of the swirler position on the combustion oscillations. Hirsch et al [10] hence investigated the effect of swirler designs and found that an additional time lag is responsible for changes in the FTF. Komarek et al [11] investigated the influence of several swirler positions on the FTF and concluded that disturbances propagate at a convective and an acoustic speed downstream the swirler position.…”

Section: Introductionmentioning

confidence: 98%

LES evaluation of the effects of equivalence ratio fluctuations on the dynamic flame response in a real gas turbine combustion chamber

Hermeth

Staffelbach

Gicquel

et al. 2013

Proceedings of the Combustion Institute

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International audienceLarge Eddy Simulations (LES) of a lean swirl-stabilized gas turbine burner are used to analyze mechanisms triggering combustion instabilities. To separately study the effect of velocity and equivalence ratio fluctuations, two LES of the same geometry are performed: one where the burner operates in a "technically" premixed mode (methane is injected by holes in the vanes located in the diagonal passage upstream of the chamber) and the second one where the flow is fully premixed in the diagonal passage. The inlet is acoustically modulated and the mechanisms affecting the dynamic flame response are identified. LES reveals that both cases provide similar averaged (non-)pulsated flame shapes. However, even though the mean flames are only slightly modified, the delays change when mixing is not perfect. LES fields and a simple model for the methane jets trajectories show that mixing in the diagonal passage is not sufficient to damp heterogeneities induced by unsteady fuel flow rate and varying fuel jet trajectories. These mixing fluctuations are phased with velocity oscillations and modify the flame response to forcing. Local fields of delays and interaction indices are obtained, showing that the flame is not compact and is affected by fluctuations of mixing

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Influence of the Swirler Design on the Flame Transfer Function of Premixed Flames

Cited by 51 publications

References 0 publications

Bistable swirled flames and influence on flame transfer functions

Bistable swirled flames and influence on flame transfer functions

Determination and Scaling of Thermo Acoustic Characteristics of Premixed Flames

LES evaluation of the effects of equivalence ratio fluctuations on the dynamic flame response in a real gas turbine combustion chamber

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