Asynchronous periodic contact modes for rotor vibration within an annular clearance

Abstract: The dynamics of a multimode rotor–bearing system are analysed when the rotor contacts with a stator having annular clearance. By transforming to a rotating frame, all possible steady state rotor vibration modes that involve periodic contact with the surround may be predicted. Using a harmonic decomposition with generalized fundamental frequency, periodic solutions are obtained for rotor motions that involve asynchronous periodic contact. The analytical solutions are compared with previously published experimental results, which are predicted with considerable accuracy thus con rming the ef cacy of the approach. Solutions are obtained for different test cases, which show how the amplitude and stability of the periodic contact modes are dependent on system parameters and operating conditions. In particular, for increased unbalance levels, the amplitude of the contact mode vibration is increased and the response of the rotor progresses from a bouncing forward whirl to a backward whirl-type motion. The nature of the identi ed rotor responses and implications for machine operation and reliability are discussed