A combustion instability in a combustor typical of aero-engines is analyzed and modeled thanks to a low order Helmholtz solver. A Dynamic Mode Decomposition (DMD) is first applied to the Large Eddy Simulation (LES) database. The mode with the highest amplitude shares the same frequency of oscillation as the experiment (approx. 350 Hz) and it 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 650–700 Hz, it is postulated that the instability observed around 350 Hz stems from a mixed entropy/acoustic mode where the acoustic generation associated with the entropy spots being convected throughout the choked nozzle plays a key role. A Delayed Entropy Coupled Boundary Condition is then derived in order to account for this interaction in the framework of a 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 solver proves able to predict the presence of an unstable mode around 350 Hz, in agreement with both the LES and the experiments. This finding supports the idea that the instability observed in the combustor is indeed driven by the entropy/acoustic coupling.
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ASME Turbo Expo 2013: Turbine Technical Conference and Exposition
June 3–7, 2013
San Antonio, Texas, USA
Conference Sponsors:
- International Gas Turbine Institute
ISBN:
978-0-7918-5510-2
PROCEEDINGS PAPER
Analysis and Modelling of Entropy Modes in a Realistic Aeronautical Gas Turbine
Emmanuel Motheau,
Emmanuel Motheau
Safran Snecma, Toulouse, France
CERFACS, Toulouse, France
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Franck Nicoud,
Franck Nicoud
University Montpellier II, Montpellier, France
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Yoann Mery,
Yoann Mery
Safran Snecma, Moissy Cramayel, France
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Thierry Poinsot
Thierry Poinsot
CNRS, Toulouse, France
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Emmanuel Motheau
Safran Snecma, Toulouse, France
CERFACS, Toulouse, France
Franck Nicoud
University Montpellier II, Montpellier, France
Yoann Mery
Safran Snecma, Moissy Cramayel, France
Thierry Poinsot
CNRS, Toulouse, France
Paper No:
GT2013-94224, V01AT04A009; 10 pages
Published Online:
November 14, 2013
Citation
Motheau, E, Nicoud, F, Mery, Y, & Poinsot, T. "Analysis and Modelling of Entropy Modes in a Realistic Aeronautical Gas Turbine." Proceedings of the ASME Turbo Expo 2013: Turbine Technical Conference and Exposition. Volume 1A: Combustion, Fuels and Emissions. San Antonio, Texas, USA. June 3–7, 2013. V01AT04A009. ASME. https://doi.org/10.1115/GT2013-94224
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