Linear Instability Analysis Method with Three-Dimensional Finite Element Model of Lean Premixed Combustor

Combustion oscillation of a self-excited combustion-acoustic phenomenon occurs inside the gas turbine combustor. In general, excessive pressure fluctuation of combustion oscillation may impair the gas turbine engine operation and may result in hardware damages. Hence, combustion oscillation has been one of the problems of the gas turbine development. For predicting the combustion-acoustic instability on the designing stage, we have developed one-dimensional linear instability analysis method and verified the analysis accuracy by premixed combustor laboratory tests. According to the prior efforts, the basic framework of combustion-acoustic system has been captured, and then, we have known that not only precise analysis method but also high precise model parameters are needed for accurate analysis. So in this paper, to achieve this, three-dimensional combustion-acoustic analysis method with finite element model which can simulate precisely the geometry and combustion state of an actual gas turbine combustor is developed. Further, for the calculation efficiency, the approximation calculation method for evaluating the complex eigenvalues of finite element model is proposed and its accuracy is validated at simple examples.