LES and experimental studies of cold and reacting flow in a swirled partially premixed burner with and without fuel modulation

Sengissen, Alois; Kampen, J.F. van; Huls, R.A.; Stoffels, Genie G.M.; Kok, Jacobus B.W.; Poinsot, Thiérry

doi:10.1016/j.combustflame.2007.02.009

Cited by 72 publications

(34 citation statements)

References 27 publications

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“…It would suggest that the approach is very general, and it has indeed been applied in a variety of simulations where partially premixed combustion would be expected. These applications include helicopter engine combustors [19], partially premixed swirl burners [20], and industrial gas turbines [21]. Results that agree well with experimentally measured velocities, temperatures, and pressure fluctuations have been obtained in each of these cases.…”

Section: Thickened Flame Modelssupporting

confidence: 57%

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Large-Eddy Simulation for Combustion Systems: Modeling Approaches for Partially Premixed Flows

Knudsen¹,

Pitsch²

2010

TOTHERJ

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Combustion models often appear in forms that are customized for specific applications. This process of customization produces modeling approaches that tend to be very different from one another in terms of cost, accuracy, and applicability. For example, many combustion models have been developed to describe either the asymptotic premixed or the asymptotic non-premixed combustion limit. These idealized regimes are chosen as the basis for modeling approaches because the associated combustion physics are understood sufficiently well to be cast in a framework that accounts for how turbulence and chemistry interact. Partially premixed regimes and regimes that involve transitions between premixed and non-premixed behavior, however, are not very well understood. Consequently, most readily available modeling approaches do not account for these mixed regimes in a very careful fashion. This presents a particular challenge to further model development, since these partially premixed and transition processes are very important in realistic combustion devices. In this review, the particular challenges associated with modeling partially premixed combustion in LES will be discussed and the applicability of common LES combustion models to partially premixed processes will be assessed.

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Section: Thickened Flame Modelssupporting

confidence: 57%

“…Thickened flame models for LES [17][18][19][20][21][22] solve transport equations for chemical species, and use Arrhenius rate expressions to describe species' reactions. These transport equations can be solved, however, only when flame structures are adequately resolved.…”

Section: Thickened Flame Modelsmentioning

confidence: 99%

Large-Eddy Simulation for Combustion Systems: Modeling Approaches for Partially Premixed Flows

Knudsen¹,

Pitsch²

2010

TOTHERJ

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“…The exit plane of the nozzle is defined as h = 0 for all measurements. The third part of the configuration is the combustion chamber which has a square cross-section (85 Â 85 mm 2 ) and is equipped with 1.5 mm thick quartz walls to enable optical measurements. The fourth part is a converging duct which connects the combustor to the atmosphere.…”

Section: The Swirled Premixed Burner Configurationmentioning

confidence: 99%

“…One important issue has been to identify the possibilities offered by simulation and especially Large Eddy Simulation (LES) to predict self-excited combustion oscillations. The specific example of swirled combustors where flames couple with acoustic modes has received significant attention [1][2][3][4] because such oscillations are often found in real gas turbines [5,6]. An important question in swirled unstable flames is the effect of mixing on stability.…”

Section: Introductionmentioning

confidence: 99%

Large Eddy Simulation of combustion instabilities in a lean partially premixed swirled flame

Franzelli

Riber

Gicquel

et al. 2012

Combustion and Flame

267

162

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a b s t r a c tThis paper investigates one issue related to Large Eddy Simulation (LES) of self-excited combustion instabilities in gas-fueled swirled burners: the effects of incomplete mixing between fuel and air at the combustion chamber inlet. Perfect premixing of the gases entering the combustion chamber is rarely achieved in practical applications and this study investigates its impact by comparing LES assuming perfect premixing and LES where the fuel jets are resolved so that fuel/air mixing is explicitely computed. This work demonstrates that the perfect premixing assumption is reasonable for stable flows but is not acceptable to predict self-excited unstable cases. This is shown by comparing LES and experimental fields in terms of mean and RMS fields of temperature, species, velocities as well as mixture fraction pdfs and unsteady activity for two regimes: a stable one at equivalence ratio 0.83 and an unstable one at 0.7. IntroductionThe instabilities of swirled turbulent flows have been the subject of intense research in the last ten years. One important issue has been to identify the possibilities offered by simulation and especially Large Eddy Simulation (LES) to predict self-excited combustion oscillations. The specific example of swirled combustors where flames couple with acoustic modes has received significant attention [1-4] because such oscillations are often found in real gas turbines [5,6]. An important question in swirled unstable flames is the effect of mixing on stability. In most real systems, combustion is not fully premixed and even in laboratories, very few swirled flames are truly fully premixed. The effects of equivalence ratio fluctuations on flame stability in combustors have been known for a long time [7,8]: changes in air inlet velocity induce variations of the flow rate through the flame but may also induce mixing fluctuations and the introduction into the combustion zone of nonconstant equivalence ratio pockets. These pockets create unsteady combustion and can generate instabilities.In many experiments, LES is performed assuming perfect mixing mainly because the computational work is simpler: there is no need to mesh the fuel injection holes or to resolve the zone where these jets mix with air. However, this assumption totally eliminates fluctuations of equivalence ratio as a mechanism of instability, thereby limiting the validity of the LES. One specific example of such limitations is reported in the experiment of [9][10][11] which has been computed by multiple groups [12][13][14][15][16]. This methane/air swirled combustor was especially built to study combustion instabilities in such systems and for all computations up to now, perfect mixing has been assumed by LES experts because methane was injected in the swirler, far upstream of the combustor, suggesting that perfect mixing is achieved before the combustion zone. Interestingly, all computations performed with perfect mixing assumptions have failed to predict the unstable modes observed in the experiments. Moreover, recent...

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“…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].…”

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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LES and experimental studies of cold and reacting flow in a swirled partially premixed burner with and without fuel modulation

Cited by 72 publications

References 27 publications

Large-Eddy Simulation for Combustion Systems: Modeling Approaches for Partially Premixed Flows

Large-Eddy Simulation for Combustion Systems: Modeling Approaches for Partially Premixed Flows

Large Eddy Simulation of combustion instabilities in a lean partially premixed swirled flame

Bistable swirled flames and influence on flame transfer functions

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