Research on the Mechanism of Sudden Increase and Sudden Decrease in Vibration

For the convenience of assembly, there is often a small clearance between the aero-engine bearing outer race and the bearing seat. During the test run of typical aero-engine with inter-shaft bearing which has small clearance, the problem of “sudden increase and sudden decrease” of the total vibration amplitude when the rotational speed is stable has occurred multiple times. Therefore, based on the dynamic model of high-speed dual-rotors, this paper conducts a mechanism study on the rotor vibration response and the change law of the fulcrum dynamic load to reveal the fundamental cause of the “sudden increase and sudden decrease” of vibration. The research results indicate that during operation, the rotor is in a high-temperature environment and is subjected to significant centrifugal load, rolling dynamic load and temperature load. Due to the lag of temperature loads relative to the change of rotational speed, the contact status of cylindrical-face between the bearing outer ring and the bearing seat may produce a sudden change, resulting in repeated sliding and impact on the interface, interface failure and the stiffness of the inter-shaft bearing changes. Finally, the motion state of the rotor changes significantly, and the vibration signal reflects the characteristics of sudden change.