In the development process of all gas turbines, the thermoacoustic behavior of the combustion system is of crucial importance for the overall performance in terms of lifetime, emissions, and operational flexibility. An efficient design process requires a methodology which is able to analyze this behavior in an early phase. This method is at the same time expected to give insight into the underlying thermoacoustic mechanisms of relevant acoustic modes. Based on an example case for an Alstom reheat combustor relying on the auto-ignition principle, the paper describes such a method for low frequency modes, which is based on unsteady reactive CFD, flame transfer function analysis and acoustic network modeling. Results are validated against full-scale engine measurements. Moreover, physical insight of the coupling mechanisms responsible for the dynamic response of the flame is given.

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