Investigation of High-Frequency Thermoacoustic Instabilities In a Jet-Stabilized Burner With Axial Stage

Abstract In the present work, self excited high frequency thermoacoustic instabilities in a jet-stabilized gas turbine combustor with an axial stage are investigated. High pressure experiments are performed for fuel mixtures that consist of hydrogen and natural gas in an optically accessible test rig. Various operating conditions are considered in the experiment that vary in fuel composition, air-fuel ratio, and geometry (i.e. the length of the mixing sections in the main burner and the axial stage). Data for pressure oscillations in the combustion chamber as well as high-speed images for OH* chemiluminescence are recorded. Depending on the operating conditions, different frequencies for high frequency instabilities are observed in a range above 2000 Hz. In particular, the length of the mixing section in the main burner along with the amount of hydrogen in the fuel, appear to be relevant for the occurrence of frequencies that are typically associated with transverse and longitudinal modes. In order to shed light on the type of modes, the experimental data are supplemented by a compressible large-eddy simulation for one operating point.