Analysis Of Nonlinear Vibration Of The Windmilling Imbalance

Rub-impact in rotor to stator in aero-engine has been a problem for a long time, but most research have focused on the range of higher rotated speed. The windmilling condition occurs in aero-engines after a fan-blade has come off during flight and the incoming airflow rotates the fan after engine shut-down and the windmilling unbalance vibration would caused by the resulting unbalanced force. Contact between rotor and stator is easily occurred and the phenomenon of nonlinear rub-impact in rotor to stator can be found by the windmilling imbalance vibration with the decreasing gap of rotor and stator while the rotor speed is low.For marginal effect, the vibration of airframe will be sharp increased and the service life of airplane is decreasing; for seriousness, permanent bending of rotor even fatal crash can be caused. Thus the nonlinear vibration of rotor system in windmilling imbalance condition needs to be studied and connection between parameters of the system and response to be established, thereby provided theoretical reference to avoid the problem of rub-impact fault occurs and to improve the safety of the aero-engine and aircraft.This project set out to gain some insight into the rotor/stator interaction and overall system nonlinear dynamics behavior in a windmill situation. A four degree-of-freedom model of the rotor/stator system has been established based on considering the assumption which refer to Gotz von Groll's research results of rigid rotor/stator and elastic support. Simulations are conducted respectively aimed at the situations include different mass radio of rotor and stator,gap size, damping and presence of friction, geometry or stiffness asymmetry and consider the wings degree-of-freedom or not. Obviously jumps and bifurcation and the nonlinear sub- &sup-harmonic phenomenon in windmilling imbalance situation can be observed through the results of simulation, thus the complexity of the problem has been shown. While the range of rotor/stator keeping in contact and the maximum of rotor amplitude and the speed of the resonance occurs are affected by different mass radio of rotor and stator, gap size, damping obviously. The effectiveness of the numerical model has been verified by comparing the analysis of these tendency with the discipline in the literature, at the same time effective reference has also been provided to avoid this problem.