Insights into the nonlinear behaviors of dual-rotor systems with inter-shaft rub-impact under co-rotation and counter-rotation conditions

Abstract

Because of the use of seals between two rotors in aero-engines, inter-shaft rub-impact becomes a possibility in dual-rotor systems. Most studies have focused on the rotordynamics of rotor–stator rub-impacts, but there are few studies about inter-shaft rub-impacts in dual-rotor systems, and the corresponding nonlinear behaviors are not well understood. This paper aims to reveal the nonlinear behaviors of a dual-rotor system with inter-shaft rub-impact. In particular, two types of operation conditions, i.e., co-rotation and counter-rotation, are considered in the analysis of rubbing dynamics. First, a dynamic model of the dual-rotor system with inter-shaft rub-impact is established based on the finite element method. Then, the modal characteristics and vibration responses are analyzed in detail through the Campbell diagram, 3D waterfall plots, time and frequency domain waveforms, etc. The results show that inter-shaft rub-impact can lead to vibration coupling of the two rotors, and consequently, the number of critical speeds is increased. Three types of rubbing motions can be observed in the dual-rotor system: continuous inter-shaft rub-impact, intermittent inter-shaft rub-impact and self-excited rubbing motion. Among them, the self-excited rubbing motion is dominated by system natural modes and usually has high amplitude, which is very dangerous to the dual-rotor system. Moreover, the rotation direction significantly affects the rotordynamics, and the dynamic characteristics under the counter-rotation condition seem more complicated.