Constructive interference of acoustic oscillations and combustion heat release can result in high-frequency thermoacoustic instabilities in gas turbine combustion chambers with high-pressure pulsations, which generate component wear and limit the safe operating range of the engine. Hence, it is essential to predict the driving potential of such high-frequency oscillations, associated with different mechanisms, to avoid thermoacoustic instabilities.

This paper mainly deals with the quantification of linear growth rates of high-frequency thermoacoustic modes in a tubular combustor of hexagonal cross-section equipped with 12 turbulent premixed jet burners using flame dynamic models, namely dynamic compression and deflection, which have been validated for turbulent swirl burners in the past. To demonstrate the applicability as well as the shortfalls of the employed flame dynamic models, the impacts of different geometrical and flow parameters on the driving potential of high-frequency thermoacoustic modes are revealed in the framework of a parameter study, which considers the variation of thermal power, air excess ratio, preheating temperature, radial position of jet burners, and diameter of the combustor. Furthermore, the impact of the equivalence ratio distribution on flame driving is assessed.

The eigenmodes and the corresponding eigenfrequencies are computed by solving the inhomogeneous Helmholtz equation with flame driving source terms in the frequency domain using the finite element method. Particularly, growth rates of the first transversal modes are predicted as a measure for thermoacoustic instability. The required reactive mean flow fields including temperature and heat release rate are obtained based on a generic flame, which is scaled to the specific operating conditions based on the literature on turbulent jet flames and on chemiluminescence measurements available for the investigated configuration.


High-Frequency Instability Driving Potential of Premixed Jet Flames in a Tubular Combustor due to Dynamic Compression and Deflection

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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