Dynamic characteristics of rotor system with additional constraint due to rub-impact

Not only excitation force but also additional constraint will be induced to the rotor system by the rubbing effects. The latter can lead to the change of rotor stiffness and damping, which affects the dynamic characteristics of the rotor further. The paper investigates the effects of the additional constraint on the rotor's natural characteristics and response through theoretical modeling and experiment testing. The results reveal that the stiffness enhancement caused by the additional constraint will increase the rotor's resonance speed and widen the resonance interval and the unstable contact region, however the influence of the damping is opposite. Meantime, the characteristics of constraint stiffness are different for different rub-impact states, which has different effects on the rotor's response characteristics. For annular rubbing, constraint stiffness is constant, which will not change rotor response characteristics. However, for partial rubbing, constraint stiffness is time-varying and non-smooth, resulting in the super-harmonic components in frequency domain and rotor's quasi-periodic motion. The conclusions are also confirmed by the experimental results. Obtained numerical and experimental results can help to understand some phenomena in the rotating machinery and could be further used for improving of more complicated models for dynamical design and enhancement of aircraft engines.