Bearing pedestal looseness dynamic model of dual rotor system and fault feature

For the bearing pedestal looseness fault of dual rotors system, after taking into account three DOF(degree of freedom) planar rigid motion of loose bearing pedestal and introducing collision recovery coefficient, a dual rotor system dynamics model including loose bearing pedestal was set up based on the dual rotor structure of experiment rig. Using the finite element method and rigid body kinematics, and adopting the Newmark-β algorithm for numerical simulation based on Timoshenko beam elements, the dynamic characteristics of the inner and outer rotors and the bearing pedestal plane rigid body motion in occurrence of bearing pedestal looseness fault were studied. Meanwhile, the loose experiments of dual rotor system under two different speeds' combination were carried out, and the experimental results were basically the same. The simulation results with the bearing pedestal looseness fault of dual rotors bench were compared, indicating loose rotor vibration displacement waveforms had “clipping” phenomenon. When the bearing pedestal looseness fault occurred, the inner and outer rotors' vibration spectrum not only contained the difference and the sum frequency between the two rotors' fundamental frequency, but also contained loose support rotor second and third harmonics components, etc; there were more low frequency spectrums containing dividing component, etc; the rotor displacement spectrum also contained fewer combination frequency components, etc; when unilateral bearing pedestal was loosened, the inner rotor axis trajectory was drawn into similar-ellipse shape. © 2016, Editorial Department of Journal of Aerospace Power. All right reserved.