Failure analysis of backward whirl motion in an aero-engine rotor

Abstract

This study focuses on the mechanism of backward whirl motion of rotor when blade-off occurs in rotor system. A relevant failure, which is attributed to a backward whirl motion of rotor after turbine blade-off, has occurred in an aero-engine during its test operation, resulting in blade-casing rubbing and bearing damage. A novel dynamic model, considering the effect of rubbing and blade-off excitation, is proposed and the governing equation is established to analyze the existence of backward whirl motion of high pressure rotor (HPR) and explain the bearing damage. The backward whirl motion is further investigated by the complex nonlinear modes in which a new parameter, named as ‘modal damping ratio’, is used to explain the amplitude-increasing phenomenon during backward whirl motion. The results show that the existence conditions of backward whirl motion for a rotor system can be determined as: 1. The instable region of backward whirl mode exists in complex nonlinear modes analysis. 2. The amplitude of rotor experiencing sudden unbalance excitation passes the damping instability point represented for instable status and enters the instable region. Results confirm the applicability of the proposed model and complex nonlinear modes method for backward whirl motion analysis.