Reserch On Dynamic Characteristics Of A Faulty Rotor System With Squeeze Film Damper

The vibration of rotating machinery has always been the focus of rotor dynamics field,especially the aero-engine.Higher requirements are put forward for its whole engine vibration due to the harsh service environment.While excessive vibration may break out for various reasons,such as imbalance,misalignment,and rub-impact of rotor and stator.Squeeze Film Damper(SFD)is widely used in aero-engine rotor system because of its simple structure and effective vibration damping capacity.However,while SFD exerts its vibration reduction effect,it also brings nonlinear factors,which change the vibration characteristics of the rotor system.In this paper,the nonlinear vibration response of a simulation aero-engine gas generator rotor system supported by SFD under fault condition was studied.The main contents of this paper are as follows:Firstly,a dynamic model of the simulation gas generator rotor system with SFD was established.The finite element model of the gas generator simulating rotor was established by Timoshenko beam element.The mathematical model of SFD and rolling bearing were formed based on the short bearing theory and Hertz contact theory respectively.Further modal tests were carried out to modify the established finite beam element model,and a comparison of critical speeds was made between the beam and solid element model to verify the accuracy.The dynamic differential equation of the rotor system under generalized load was obtained,and the dynamic response of the system was solved by the method of combining Newmark βand Newton Raphson.Then the dynamic characteristics of the rotor system under unbalance faults were studied,and the damping effect of SFD on the unbalance faults was discussed based on the established calculation model.Under the initial unbalanced fault conditions,the vibration reduction effects of SFD and its typical bistable phenomenon were studied,and the time-frequency characteristics and bifurcation characteristics of SFD supported rotor system were analyzed in detail.For sudden unbalanced fault conditions,the suppression effects of SFD support and elastic support on sudden transient response were compared,and the bifurcation characteristics of the rotor system operation were analyzed using the magnitude of the unbalanced fault as a parameter.Results show that SFD can effectively reduce the resonance amplitude of the rotor system under the initial unbalance fault,and a larger unbalance fault is more likely to lead to the bistable phenomenon.Sub-harmonic response and multi-period motion appear in the gas generator simulation rotor system at high rotation speed.SFD can suppress the amplitude of transient response and change the vibration characteristics of the rotor system under sudden unbalanced faults,and the motion characteristics of the rotor system varies as the magnitude of unbalanced faults changes.Finally,the vibration characteristics of the rotor system under the coupling action of unbalanced and other common faults were studied respectively.For misalignment-unbalance fault conditions,the dynamic response of the rotor system was studied and the effect of SFD on misalignment faults was discussed.For rub-impact and unbalance faults,the non-coordinated precession phenomenon of the rotor system was investigated,and the system motion laws under different parameters were analyzed.For static eccentricity-unbalance conditions,the oil film force characterization formula of SFD was derived based on Reynolds boundary conditions,furtherly the influence of static eccentricity on the critical speed and bearing capacity was studied.Results show that the misalignment and unbalance faults change the characteristics of precession trajectory and cause the double frequency vibration,and SFD can suppress its large amplitude.The rubbing-misalignment fault not only changes the characteristics of precession trajectory,but also causes sub-harmonic response and multi-periodic motion.Under the static eccentricity and imbalance condition,the critical speed of the rotor system increases and resonance amplitude decreases as static eccentricity ratio expands.Static eccentricity also weaks carrying capacity of SFD,and reduces its vibration reduction efficiency at the maximum load capacity.Through analysis above,the vibration response characteristics of SFD-supported simulation gas generator rotor system under different faults conditions were revealed,which can provide theoretical reference for the design and fault diagnosis of aero-engine rotor system.