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In this work, we investigate high-frequency thermoacoustic instabilities in a jet-stabilized gas turbine burner by means of large-eddy simulation (LES). This burner is operated at 8 bar pressure with a mixture of hydrogen and natural gas. Experimental data for the pressure oscillations in the combustion chamber are provided here to validate the simulations. The LES is conducted using a splitting scheme for solving the equations for compressible, reactive flows. To model the filtered chemical source terms in LES, two different models (namely an assumed probability density function (APDF) model and a thickened flame (TF) model) are used. Time-resolved computational data are analyzed using multiresolution proper orthogonal decomposition. It is found that mainly three longitudinal modes and one mixed transverse–longitudinal mode cause the high-frequency instabilities in the combustor. Computed frequencies of these modes agree excellently with measured frequencies. Amplitudes of the modes are best reproduced by the use of the TF model. Further analysis of the computational data obtained with the TF model reveals that heat release fluctuations caused by periodic distortion of the flame geometry and by fluctuations in equivalence ratio play an important role in the thermoacoustic feedback.
Fiolitakis et al. (Mon,) studied this question.