Experimental Investigation of Limit-Cycle Oscillations in an Unstable Gas Turbine Combustor

This paper describes an experimental investigation of the characteristics of limit cycle oscillations in an unstable gas turbine combustor simulator. This investigation was performed to improve the current understanding of the nonlinear processes controlling these oscillations. Such an understanding is needed in order to predict instability amplitudes, to aid in correlating data, and to develop and optimize active control methodologies. The paper first describes an analysis of the statistical and temporal features of the limit cycle pressure oscillations, and discusses the role of system nonlinearities upon these oscillations. Next, it discusses the important role that the combustor inlet velocity plays in determining the amplitude of the limit cycle oscillations. The paper also presents data illustrating the characteristics of the combustor's transition from stable to unstable operation, and shows that these characteristics can be used to predict the occurrence of nonlinear phenomenon (e.g., hysteresis) that are often observed in unstable combustors. Finally, it is shown that inherent noise in the system can strongly affect the limit cycles, and may even be responsible for causing the combustor to become unstable under nominally stable conditions. The paper concludes with a discussion of the implications of these results on the current understanding of self-excited, combustion driven oscillations in lean, premixed gas turbine combustors.