Abstract
Vibration amplitudes and fatigue life in multistage turbomachinery are commonly estimated by an isolated investigation of the individual stages. Research is currently extending the scope to include inter-stage coupling of structural dynamics and aeroelasticity, i.e. aerodynamic coupling. These two effects have been shown to significantly influence blade vibrations. For safe operation of modern blisk blading with its lower structural damping due to the elimination of frictional contacts at the blade roots, an accurate prediction of the vibration behavior in multistage configurations with mistuning is necessary to avoid high cycle fatigue (HCF) failures.
In this paper, a cyclic Craig-Bampton reduction method with a priori interface reduction for multistage rotors is extended to handle aeroelastic effects. These reduced order models efficiently predict forced response in multistage applications. Aeroelastic multistage simulations are carried out using the harmonic balance method to account for the stage interactions and yield damping and stiffness coefficients, as well as modal excitation forces. Small structural mistuning is projected onto the tuned system modes of the rotor. The reduced order approach is applied to a two-stage compressor configuration. Monte Carlo simulations show the sensitivity of vibration amplitudes to the aeroelastic coupling for mistuning. The aeroelastic inter-stage coupling is found to originate mainly from acoustic mode propagation between the rotor stages. The fatigue of rotor blades is significantly affected by multistage interaction since vibration amplitudes increase due to the superposition of the vibration responses of multiple modes. This leads to the conclusion that aeroelastic multistage effects need to be incorporated in future design procedures to allow for an accurate prediction of fatigue life of compressor rotors.
