For the development of modern Low-NOx gas turbine combustors featuring high power densities due to their compact design a detailed knowledge about thermoacoustically induced combustion oscillations is required. In order to design passive and active means to suppress thermoacoustic oscillations and to extend the stable operation range of the gas turbine an investigation of the acoustic eigenmodes of the combustor already in the design phase is necessary. In a combined experimental and computational project, tools to determine the mode shapes of a gas turbine combustor have been developed. The mode shapes of an annular combustor of the 3A series have been identified under operating conditions in the test bed of Berlin by cross correlating pressure signals mounted on twelve different azimuthal locations. These data have been used in order to validate the new numerical steady state response method. It has been found that taking into account appropriate acoustic boundary conditions at the burner outlet the numerical predictions are in good agreement with the measurements.

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