Modeling and Simulation Analysis of Dual-Rotor System in the Early Stage of Bearing Pedestal Looseness

In order to quickly capture and analyze the dynamic characteristics of the dual-rotor system at the beginning of bearing pedestal looseness, an 8-degree-of-freedom dynamic model of the dual-rotor system including a gyroscopic moment and a loosening fault is developed. The Newmark-β method is used to solve the developed model. The dynamic characteristics of the dual-rotor system at different speeds when the bearing pedestal first starts to loosen is analyzed. A dual-rotor fault simulation test bench is built to simulate the bearing pedestal looseness fault. The comparison results show that the dynamic simulation results are in good agreement with the test results, and the fault frequency distribution pattern in the envelope spectrum of the simulation results is consistent with that of the test results, which proves the validity of the proposed dynamics model. It is also found that there is a clipping phenomenon in the rotor vibration signal when the bearing pedestal first starts to loosen. There are high pressure and low pressure rotor rotation frequency, multiplication frequency and sum frequency in the fault characteristic frequency of the dual-rotor system. Compared with the late stage of bearing pedestal looseness, the fractional frequency and 3-times frequency do not appear in the frequency spectrum of the loose rotor. Loose rotor axis orbit changes more obviously in the higher speed, showing a quasi ellipse.