Large eddy simulation of piloting effects on turbulent swirling flames

Sengissen, Alois; Giauque, Alexis; Staffelbach, Gabriel; Porta, Mauro; Krebs, Werner; Kaufmann, Peter; Poinsot, Thiérry

doi:10.1016/j.proci.2006.07.010

Cited by 47 publications

(31 citation statements)

References 28 publications

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“…A compressible LES code [4,12,[22][23][24][25][26][27][28][29][30][31][32] is used to solve the Navier-Stokes equations on hybrid (structured and unstructured) grids with real thermo-chemistry. A Taylor-Galerkin weighted residual central distribution scheme is used for the numerical integration [28,33,34].…”

Section: The Numerical Setupmentioning

confidence: 99%

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

Franzelli

Riber

Gicquel

et al. 2012

Combustion and Flame

280

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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Section: The Numerical Setupmentioning

confidence: 99%

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

Franzelli

Riber

Gicquel

et al. 2012

Combustion and Flame

280

162

View full text Add to dashboard Cite

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“…The flame sub-grid scale wrinkling and interactions at the Sub-Grid Scale (SGS) level are thus supplied by an efficiency function [8,15]. The DTF approach has successfully been used in a wide variety of configurations [2,5,16,26,27,29,33].…”

Section: Chemical Kineticsmentioning

confidence: 99%

Using LES to Study Reacting Flows and Instabilities in Annular Combustion Chambers

Wolf

Balakrishnan²,

Staffelbach³

et al. 2011

Flow Turbulence Combust

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Open Archive TOULOUSE Archive Ouverte (OATAO) OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. Abstract Great prominence is put on the design of aeronautical gas turbines due to increasingly stringent regulations and the need to tackle rising fuel prices. This drive towards innovation has resulted sometimes in new concepts being prone to combustion instabilities. In the particular field of annular combustion chambers, these instabilities often take the form of azimuthal modes. To predict these modes, one must compute the full combustion chamber, which remained out of reach until very recently and the development of massively parallel computers. Since one of the most limiting factors in performing Large Eddy Simulation (LES) of real combustors is estimating the adequate grid, the effects of mesh resolution are investigated by computing full annular LES of a realistic helicopter combustion chamber on three grids, respectively made of 38, 93 and 336 million elements. Results are compared in terms of mean and fluctuating fields. LES captures self-established azimuthal modes. The presence and structure of the modes is discussed. This study therefore highlights the potential of LES for studying combustion instabilities in annular gas turbine combustors.

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“…24 hybrid combustors are mounted around the circumferential direction of this combustion chamber, the structure of which is shown in figure 1. Advantages of flame stability of the diffusion flame and a lean premixed flame are combined and provide premixed Dry-Low-NOx (DLN) combustion [29]. Pilot fuel nozzles are mounted in the center of the hybrid combustor [30].…”

Section: Combustion Chambermentioning

confidence: 99%

“…Due to the on-linear nature of large scale energetic motions and linear nature of small scale energetic motions, large scale energetic motions are directly resolved explicitly, while the sub-grid scale motions are modeled in LES approach [29]. A Favre filter is applied to the conservation equations of mass, momentum and energy yields [22].…”

Section: Numerical Simulationsmentioning

confidence: 99%

LES of Swirl Angle on Combustion Dynamic and NOx Formation in a Hybrid Industrial Combustor

Shi¹,

Fu²,

Shen³

et al. 2016

IJHT

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Impact of diagonal swirler vane angle on combustion dynamic and NOx formation characteristic in a hybrid industrial combustor is numerically studied using a full compressible large eddy simulation approach. The predicted results show that increase the swirler vane angle enlarges the magnitude of the CTRZ and thus the coherent structure and off-axis motions of vortex cores which increase the pressure oscillations amplitude. Phenomenon of combustion instability does not occur due to the introduction of pilot diffusion flame. Formation rate of NOx is relatively slower in pilot diffusion flame, because excess air contained in pilot fuel streams dilutes the flame temperature. Regions with peak flame temperature and maximum formation rate of NOx located in vicinity to the sidewall of combustion chamber especially in the shell side. Proper increase of diagonal swirler vane angle to enlarges the divergence angle of flame and reduces the recirculation of hot gases and combustion products in outer recirculation zones to control peak temperature of flame is an effective means to control NOx emissions for this hybrid industrial combustor. Further increase the diagonal swirler vane angle will have relatively smaller impacts on compressing the NOx emission due to the confinement of combustion chamber.

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Large eddy simulation of piloting effects on turbulent swirling flames

Cited by 47 publications

References 28 publications

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

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

Using LES to Study Reacting Flows and Instabilities in Annular Combustion Chambers

LES of Swirl Angle on Combustion Dynamic and NOx Formation in a Hybrid Industrial Combustor

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