Vibration Behavior of Dual-Rotor Caused by Maneuver Load and Intershaft Bearing Defect

This paper concentrates on the vibration amplitude modulation and frequency modulation behavior of a dual-rotor system induced by the maneuver load and defective intershaft bearing. The motion equations of a dual-rotor system are presented by considering the intershaft bearing force with a local defect of the outer raceway and the maneuver load of a barrel-roll flight. The fourth-order Runge-Kutta method is employed to study the vibration responses of the dual-rotor system, which are reflected by the time history curves, the bearing contact force curves, and the Hilbert envelope spectra. It is shown that the rotor responses display impulse vibrations due to the defective intershaft bearing; and the corresponding Hilbert envelope spectra contain defect characteristic frequencies, multiple defect frequencies, side frequencies, and modulation frequencies. The results reveal the frequency modulation behavior of the impulse vibrations induced by the rotating speed ratio and the amplitude modulation behavior influenced by the maneuver load, the bearing defect span, and the rotating speed. Finally, defective intershaft bearing experiments under maneuvering flight are conducted, confirming the availability of the numerical vibration amplitude modulation and frequency modulation behavior. This analysis provides a theoretical foundation for bearing state detection during flight maneuvers.