SELF-EXCITED OSCILLATIONS OF A ROTOR CAUSED BY THE CLEARANCE BETWEEN BEARING OUTER RING AND PEDESTAL WITHOUT CONSIDERING THE TIGHTENING TORQUE

Squeeze film damper is widely used in aeroengines. Clearance occurs between the bearing outer ring and the pedestal due to oil leakage, which causes nonlinear resonances of self-excited oscillation, subharmonic, super-harmonic and combination oscillation in the system response. In order to reveal the mechanism of nonlinear oscillation, a rotor system model of bearing outer ring and pedestal with clearance is established. In order to reveal the strong nonlinear phenomenon between the bearing outer ring and pedestal, the influence of the bearing end plate on the friction moment of the bearing outer ring is ignored, while the collision between bearing outer ring and pedestal is considered and its collision model is established. Using the Runge-Kutta method to numerically solve the motion equation, the time domain curve, the orbit of shaft center and the frequency of disk and rotor under the typical speed of self-excited oscillation occurred in the system are obtained. It is found that the clearance between bearing outer ring and pedestal shows complex nonlinear phenomena, including sub-harmonics, super-harmonics self-excited oscillation and combined resonance, which provides a theoretical basis for diagnosing the nonlinear vibration induced from the clearance between bearing the outer ring and the pedestal.