Response of partially premixed flames to acoustic velocity and equivalence ratio perturbations

Kim, Kyu Tae; Lee, Jong Guen; Quay, Bryan D.; Santavicca, Domenic A.

doi:10.1016/j.combustflame.2010.04.006

Cited by 108 publications

(50 citation statements)

References 30 publications

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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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“…• Second, basic experiments studied in labs are usually operated at atmospheric pressure (Lawn et al 2004;Kornilov et al 2009;Karimi et al 2009;Kim et al 2010) to ease the technological issues. This means that the combustor chamber is not connected to a choked nozzle, eliminating any contribution of the indirect noise effect ab initio.…”

Section: Introductionmentioning

confidence: 99%

Mixed acoustic–entropy combustion instabilities in gas turbines

2014

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A combustion instability in a combustor terminated by a nozzle is analysed and modelled based on a low order Helmholtz solver. A Large Eddy Simulation (LES) of the corresponding turbulent, compressible and reacting flow is first performed and analysed based on Dynamic Mode Decomposition (DMD). The mode with the highest amplitude shares the same frequency of oscillation as the experiment (approx. 320 Hz) and shows the presence of large entropy spots generated within the combustion chamber and convected down to the exit nozzle. The lowest purely acoustic mode being in the range 700 − 750 Hz, it is postulated that the instability observed around 320 Hz stems from a mixed entropy/acoustic mode where the acoustic generation associated with entropy spots being convected throughout the choked nozzle plays a key role. The DMD analysis allows to extract from the LES results a low-order model that confirms that the mechanism of the low-frequency combustion instability indeed involves both acoustic and convected entropy waves. The Delayed Entropy Coupled Boundary Condition (Motheau et al. 2014) is implemented into a numerical Helmholtz solver where the baseline flow is assumed at rest. When fed with appropriate transfer functions to model the entropy generation and convection from the flame to the exit, the Helmholtz/DECBC solver predicts the presence of an unstable mode around 320 Hz, in agreement with both LES and experiments.

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“…This method includes the following steps: 1) Calculating the BTM calculated by the FEM or ANM described above, 2) Choosing the self-excited frequencies from the pressure signals, 3) Solving the acoustic pressure and velocity at the plenum with the self-excited frequencies by the MMM, 4) Calculating the acoustic pressure according the eqn (10)(11)(12) and comparing the measurement values at point x 4 . Sound pressure level (SPL) from measuring point x 4 varies with the change of frequency as demonstrated in Fig.8 it shows total about eight resonance frequencies excited by the combustion instability in the range from 10 to 500Hz, which will be used in the next calculation.…”

Section: Experiments Validation Resultsmentioning

confidence: 99%

“…Dowling et al [17,18] treated the burner as a simple duct or tube with constant cross section and length in a network model. Actually, it is also important to consider the real geometry of swirler burner for the effects of fuel impedance [19] and acoustic propagation in the swirler burner [10]. Fischer et al [20] split the burner into several elements with serial connections, and the BTM was obtained by multiplying the transfer matrices of all the elements.…”

Section: Introductionmentioning

confidence: 99%

Computation of Acoustic Transfer Matrices of Swirl Burner with Finite Element and Acoustic Network Method

Yang

Zhang

Fang

et al. 2015

Journal of Low Frequency Noise, Vibration and Active Control

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For a gas turbine combustor, an accurate transfer matrix of the burner is an essential prerequisite for stability analysis of combustion instability. This paper describes two numerical methods for the computation of burner transfer matrix (BTM) derived from the experimental method and an experimental validation. In the numerical study, Helmholtz equation with the boundaries of plane wave radiation is solved by employing a finite element code. As alternative to the finite element method (FEM), the BTM is also assessed through using acoustic network method (ANM). In the experimental study, complex acoustic pressure at the combustion chamber firstly can be evaluated based on multi-microphone method (MMM) from three measurement points in the plenum and BTM calculated by the FEM or ANM, then be compared with the measurement for the BTM validation at resonance frequency self-excited by the combustion instability of the combustor consisting of a supply plenum, a premixed swirlstabilized burner and a combustor chamber. The validation shows that the three calculated values are essentially the same as the experimental data, when resonance frequency approximately equal to194, 243 and 290Hz. The results indicate that acoustic behavior of the complex swirl burner can be evaluated successfully by mapping the burner to a network consisting of simple elements.

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Response of partially premixed flames to acoustic velocity and equivalence ratio perturbations

Cited by 108 publications

References 30 publications

Bistable swirled flames and influence on flame transfer functions

Bistable swirled flames and influence on flame transfer functions

Mixed acoustic–entropy combustion instabilities in gas turbines

Computation of Acoustic Transfer Matrices of Swirl Burner with Finite Element and Acoustic Network Method

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