Interaction of flutter and forced response in a low pressure turbine rotor with friction damping and mistuning effects

Abstract

In modern LPT designs, which typically can assume a tolerable level of flutter, the simultaneous presence of forced response and flutter in different operation regimes becomes unavoidable. Current design rules rely on the linear superposition of vibration levels from the isolated problems. However, recent evidence from reduced order model calculations and from experiments suggests that this may be an over conservative approach. In order to check this finding, this study examines the flutter and forced response interaction in a realistic low pressure turbine rotor. A high fidelity model is used, and an efficient numerical method is implemented for the computation of the aeroelastic vibrations of the rotor with nonlinear friction effects at the blade-disk contact interfaces. A hybrid approach is used that combines a traveling wave description for the linear modes with a physical space representation for the displacement of the nonlinear contacts. The resulting equations are integrated in the time domain in order to account for the unknown flutter frequencies present in the response. Both tuned and mistuned configurations are considered, and it is confirmed that the actual response of the system is much smaller than that coming from the linear superposition of the separated effects.