Dynamic characteristics analysis of a rotor–stator system under different rubbing forms

Dynamic characteristics of a rotor rubbing with circular stator and four pin shape stators are studied based on contact dynamics theory. Based on finite element (FE) method, the rotor system attached with two disks and pin shape stators are simulated by Timoshenko beam. The circular stator is simulated by a lumped mass model, and the rotor and stator are connected by one or more point–point contact elements to establish the dynamic model of the rotor–stator coupling system. Assuming that the rubbing is caused by the sudden impact excitation and sudden unbalance excitation under two loading conditions (condition 1: in-phase unbalances of two disks at the first critical speed, condition 2: out-of-phase unbalances of two disks at the second critical speed), the system dynamic characteristics are analyzed by the time-domain waveform, rotor orbit, normal contact/rubbing force and stator acceleration. The results show that the rubbing caused by the sudden impact under the loading condition 2 will always exist and the rubbing will excite quasi-periodic motion of the rotor system; combination frequency components about the rotating frequency (1×) and the first lateral natural frequency of the rotor–stator coupling system (fn1) can be viewed as the most distinguishable characteristic. Full annular rubbing may appear due to the sudden unbalance excitation under the loading condition 1, the four-point rubbing can restrain the subsynchronous vibration and mainly excites odd multiple frequency components, such as 3× and 5×.