Modeling and dynamic characteristics analysis of bearing pedestal early looseness in dual-rotor system

Abstract

In order to study the dynamics in a dual-rotor system in the presence of a bearing pedestal early looseness fault, a 12-degree-of-freedom dual-rotor system bearing pedestal looseness fault dynamic model considering gyroscopic moments is developed. The Newmark-β method is used to solve the developed model. The dynamic response characteristics of the dual-rotor system when the bearing pedestal is loosened are analyzed. A dual-rotor fault simulation test bench is built to carry out bearing pedestal looseness fault simulation experiments. The comparative results show that the fault frequency distribution pattern in the simulation analysis envelope spectrum is consistent with the experimental results, which proves the validity of the proposed dynamics model. It is found that there is clippings in the rotor vibration signal when there is a bearing pedestal early looseness fault in the dual-rotor system. In the envelope spectrum there are high and low pressure rotor rotation frequency, the sum of frequencies and 2-fold the characteristic frequency of rotor rotation frequency. With the increase of rotational speed ratio, the amplitude of envelope spectrum characteristic frequency increases. When the bearing pedestal is loose, the loose rotor axis trajectory is elliptical-like, and the rotor axis trajectory has a tendency to be more chaotic. Capturing the vibration signal characteristics of a dual-rotor system at very small loosening angles is necessary for preventing larger looseness, which is crucial for fault prediction.