Analysis Of Coupled Bending-torsion Vibration Of Aeroengine Dual-rotor Systems With Rub-impact Fault

Rub-impact is a common fault in aeroengine rotor system.When rub-impact occurs,the bending vibration and torsional vibration of the system will show abundant dynamic characteristics.Understanding these fault characteristics can provide a basis for rub-impact fault diagnosis of aeroengines.In this paper,the coupled bending-torsion vibration characteristics of a five-point supported aeroengine dual-rotor system under rub-impact fault are studied by numerical simulation and experiment.The main work can be divided into the following aspects:1.A simplified model of five-point supported aeroengine dual-rotor system is established.Elastic support,dual-frequency excitation and intermediate bearing are taken into account in the model.In addition,the coupled bending-torsion dynamic equation of the system is derived by using Lagrange equation.2.As for bending and torsional coupling dynamic equations with rubbing force,the Runge-Kutta method is used for numerical calculation.Combined with waterfall map,spectrum diagram,the spectral characteristics of the bending vibration and torsional vibration are analyzed.The torsional vibration of the rotor experimental platform is measured by incremental encoders to verify the spectral characteristics obtained from the simulation analysis.The research results show that the torsional vibration exhibits characteristic frequencies are similar to bending vibration,including multiple frequency,fractional frequency,and combined frequency of working frequency and multiple/fractional frequency,but they are more obvious in the torsional vibrations.3.The bifurcation and chaos characteristics of bending and torsional vibration are analyzed by choosing the speed,eccentricity,stator clearance,contact stiffness and friction coefficient of the system as bifurcation parameters.The results show that bending vibration and torsional vibration have similar bifurcation process and the same bifurcation point,and there are amplitude jumps at each bifurcation point.The process of bifurcation is very complex.The system shows alternating state changes of singleperiod motion,three-period motion,five-period motion,multiple-period motion,almost-periodic motion and chaotic motion with the change of bifurcation parameters.4.The transient response characteristics of bending vibration and torsional vibration caused by rub-impact fault under sudden unbalanced excitation are studied.The results show that the natural frequencies of bending vibration and working frequency are shown in the transient response of bending vibration;the natural frequencies of torsional vibration are shown in the transient response of torsional vibration.Moreover,the natural frequency components of bending vibration are transmitted to the torsional vibration through the coupling of bending and torsion,which expresses as the combined frequency components of the natural frequency of bending vibration,the working frequency and the natural frequency of torsional vibration.Because of the restraint effect of the casing,the natural frequency of the bending vibration increases,which makes it difficult to judge the frequency component in the transient response,while the torsional vibration frequency will not change.Therefore,the natural frequency component of the torsional vibration in the transient response can be used as a diagnostic signal for rubbing fault.In this paper,the bending-torsion coupling vibration characteristics of aeroengine twin-rotor system under rub-impact fault are studied by simulation and experiment,which can provide reference for aeroengine fault diagnosis.