Effect Of Surface Waviness And Elastohydrodynamic Lubrication Of Intershaft Bearing On The Dynamic Characteristics Of Dual Rotor

Intershaft bearing is the key and weak part connecting the high-pressure rotor and low-pressure rotor of aero-engine.The surface waviness and elastohydrodynamic lubrication(EHL)of intershaft bearing have the affect of the dynamic characteristics of dual rotor system.In order to understand the vibration characteristics of intershaft bearing-dual rotor system,this work researched the dynamic characteristics of intershaft bearing-dual rotor system considering the surface waviness and EHL of intershaft bearing.The main work and conclusions are as follows:1.The dynamic characteristics of dual rotor system,the dynamic characteristics of the rolling bearing and rotor system considering the surface waviness of the rolling bearing and the dynamic characteristics of rolling bearing and rotor system considering the EHL were reviewed.2.According to the Lagrange equation,a four-point support dual rotor system model of aero-engine considering the intershaft bearing surface waviness is established.And the nonlinear dynamic equation of the system is solved by Runge-Kutta method.The results show that the surface waviness of the intershaft bearing have significant influence on the dynamic characteristics of dual-rotor system,especially at the lower speed,which is mainly reflected in:(1)The surface waviness can intensify the change of time-varying stiffness of the intershaft bearing,especially at the lower speed,the surface waviness have significant influence on the time-varying stiffness of the intershaft bearing.(2)The surface waviness of intershaft bearing increases the amplitude and fluctuation of the bearing force at the lower speed.(3)After considering the surface waviness,jump and hysteresis phenomenon occurs on the main resonance peak in the process of acceleration and deceleration.The region of hysteresis phenomenon is related to the constant clearance of surface waviness and the number of rolling elements.(4)The surface waviness of intershaft bearing causes the continuous spectrum in the spectrum diagram at the lower speed,while at the higher speed,the frequency component of the system is not significantly different from the ideal intershaft bearing-dual rotor system.(5)After considering the surface waviness of intershaft bearing,the bifurcation and chaos characteristics of the dual rotor system is more complicated at the lower speed.3.Established the dual rotor system model considering the EHL of intershaft bearing by using the theory of rotor dynamics and lumped-mass method.The vibration characteristics are examined by numerical simulation.By compared with the system ignoring the EHL,study the influence of EHL to the dynamic characteristics of dual rotor system.The conclusions indicate that:(1)From the amplitude-frequency curve,EHL makes the second order resonant peak of the high-pressure rotor and low-pressure rotor move to right and the amplitude at the resonant peak decreases,but it has little effect on the first order resonant peak.(2)Change the Hertz contact stiffness and radial clearance of intershaft bearing,compared with the condition of ignoring the EHL,when considering the EHL,the first order resonant peak amplitude change is less than 5%,the second order resonant peak amplitude change is between 4% and 9%.And the position of the first order resonant peak is not offset,while the position of the second order resonant peak move to high frequency direction about 2% to 8%.Change the viscosity of lubricating oil,the influence percentage of the low-pressure rotor and highpressure rotor is less than 1%.(3)Compared the experimental results with the simulation results,in the experimental speed range,the relative change of the vibration amplitude of the system is less than 4% when considering the EHL of the intershaft bearing.The results of the simulation and experiment are consistent.(4)EHL has weak inhibitory effect on the transient response,and the attenuation time of free vibration will not be shortened.Therefore,considering EHL is of great significance for the transient response analysis of dual rotor system.(5)The shape of the intershaft bearing force-speed curve does not change after considering the EHL,while the resonance peak move to high speed direction.At the lower speed,time domain waveform of bearing force is disordered after considering the EHL.With the increase of speed,the time domain waveform of bearing force is approximately sinusoidal,regardless of whether the EHL is considered.4.The conclusions of this work have theoretical guiding significance to understand the nonlinear vibration characteristics and to optimize the parameters of intershaft bearing-dual rotor system.And this work can also provide a theoretical foundation for fault diagnosis of the aero-engine.