Research On Transient Dynamic Characteristics Of Aeroengine Rotor Systems Under Maneuvering Flight Environment

Aeroengines not only have complex structures and high operational parameters(high rotating speed,high temperature,and high pressure),but also endure extreme maneuvering flight environments.When an aircraft completes various maneuvering flight actions,aero-engine rotor systems will bear the additional inertial excitation,which can lead to the instability of rotor systems,aggravation of typical vibration faults and even the engine damage or flameout.In this paper,the dynamic modeling and transient response analysis of aero-engine rotor systems in maneuvering flight environments are taken as the main line.The transient disturbance influence of maneuvering flight on rotor responses is studied considering the coupled nonlinear supports of ball bearings and squeeze film dampers(SFDs),or different typical faults(such as local defect of inter-shaft bearing,rub impact fault,and coupled rub impact fault,etc.)The vibration mechanism and typical fault characteristics of rotor responses induced by the maneuvering flight are given.The main conclusions are as follows.(1)Considering the nonlinear supports of ball bearings and squeeze film dampers(SFDs),the nonlinear dynamic behavior of an asymmetric rotor system under maneuvering flight is studied.The effects of the translational acceleration motion,angular motion and transient pitching flight of an aircraft on the vibrations of rotor systems are analyzed.The bistable phenomenon,amplitude jump behavior and non-synchronous vibrations of the rotor system under maneuvering flight are mainly revealed.A critical flight parameter is found to correspond to the vibration instability of the rotor system.(2)The impulse vibration behavior of a dual-rotor system subjected to maneuver load is studied considering the local defect of inter-shaft bearings.The influences of system parameters(including rotor parameters and flight parameters)on the impulse vibration responses of dual-rotor systems are analyzed.Through simulation and experiment method,a general rule about impulse vibration frequency modulation phenomena caused by different rotation speed ratios is given.It is found that the impulse vibration amplitue of rotor systems will increase under the condition of maneuver load,and the side frequencies amplitude in Hilbert envelope spectrum also increases greatly.The fault characteristic amplification phenomena of rotor responses casued by the maneuver load environment can be useful for bearing damage fault detection.(3)It is found that there are paroxysmal impulse vibration phenomena when dual-rotor systems reach some special rotation speed ratios.The differences between the paroxysmal impulse vibration and general impulse vibration are analyzed.The dynamic phenomena,physical mechanism and occurrence conditions of the paroxysmal impulse vibration are given.An analytical formula related to the rotation speed ratio is derived,which can well predict the occurrence condition of paroxysmal impulse vibrations.At last,some experimental cases are executed,proving the dynamic phenomena and occurrence condition of the paroxysmal impulse vibrations.(4)The rub impact responses of dual-rotor systems caused by maneuvering flight are studied.The transient time-frequency characteristics of the bending and torsion vibration of rotor systems are analyzed It is found that the unbalance torque and friction torque caused by the rub-impact are the main factors leading to the bending-torsional coupling motions of rotor systems.The influences of system parameters,including the rub-impact stiffness,friction coefficient and rotating speed,on the bending and torsional motions of the dual-rotor system are investigated.The fault characteristics of the bending and torsional motions of the rotor system induced by the transient rub-impact fault are concluded.The difference and connection between the time-frequency characteristics of the bending and torsional vibrations are also given.(5)The nonlinear vibration phenomenon of a rub-impact fault rotor and a coupled rub-impact fault rotor with misalignment is investigated with the consideration of aircraft barrel roll flight.The nonlinear responses of two types of rub-impact fault rotors under rotor acceleration or constant rotation speed and aircraft at varied rolling speeds are investigated.The internal vibration connection and difference between the rub-impact fault rotor and coupled rub-impact fault rotor with misalignment are studied while considering the aircraft barrel roll flight.The results can be used for multi-fault detection of aircraft rotor systems during flight maneuvers.