Research On Dynamic Characteristics Of Elastic Ring Squeeze Film Damper Integrated Ball Bearing

Main bearings of an aero-engine combined with elastic ring squeeze film damper(ERSFD,short for damper)benefit the attenuation of nonlinear vibrations in the rotor system.However,such a damper creates an oil film reaction force on the bearing and allows the outer ring to whirl from a relatively fixed state,affecting the dynamic response of the bearing.Previous studies have widely focused on the dynamic characteristics of the oil film and the response of the ERSFD supported rotor,ignoring bearing nonlinear excitation.As well,no contributions have been documented about the effect of ERSFD on the dynamic characteristics of the main bearing.This thesis takes an ERSFD integrated ball bearing as the research object,and performs dynamic modeling,dynamic analysis and experimental research.The ball contact excitation is incorporated into ERSFD by using the discrete element method.High-speed bearing performance and large-thrust load conditions are considered so as to establish parametric nonlinear dynamic models for the inner and outer rings.These models build theoretical foundation for the bearing dynamic analysis.Subsequently,an analytical thin-walled ring and turbulent-jet orifice ERSFD model was explored.This model is used to solve the oil film reaction condition required in the bearing model.Based on the bearing model and known oil film reaction force,the dynamic response of the inner and outer rings in terms of displacement and velocity is analyzed numerically.The effect of ERSFD structure and operating parameters on the dynamics of the bearing in steady and transient state is uncovered.Finally,an ERSFD & Ball Bearing Dynamic Tester was constructed to examine the theoretical model.The main research work and highlights of this thesis are as follows:1.A dynamic model of the ERSFD integrated ball bearing was developed,laying a theoretical foundation for the study of the influence of ERSFD structural parameters on the dynamic characteristics of the bearing.The contact load excitation of the ballouter raceway is combined into the ERSFD model by using the discrete element method.In addition,quasi-static bearing model was further developed according to the relationship of displacement-elastic contact approach among the inner ring,outer ring and ball.In the dynamic model,the ball centrifugal force,the variation of operating contact angle and the large-thrust load condition of aero-engine are considered.The results show that the outer ring whirls under the control of a four-dimensional autonomous nonlinear dynamic system.Its dynamic behavior is related to the oil film force,bearing speed,squirrel cage spring support stiffness,elastic ring support stiffness and gravity parameters;the motion of the inner ring evolves following a seven-dimensional autonomous nonlinear dynamic system.Its dynamic behavior is associated with rotor unbalance,rotor speed,applied loads and gravity parameters.2.An analytical model of ERSFD was established for the study of oil film properties.In this model,the deformation of the elastic ring and the net outlet flow rate of the orifice are calculated,and the effect of the ERSFD structure and operating parameters on the oil film pressure and oil film force characteristics are investigated.The results show that as the flexibility of the elastic ring increases by a factor of 20,the maximum pressure in the inner and outer chambers is decreased by 86% and increased by a factor of 2.3.The flexibility of the elastic ring highly affects the oil film pressure in the inner chamber.As the orifice diameter decreases by half,the maximum pressure in the inner and outer chambers is increased by a factor of 2.99 and 3.99 respectively.The diameter of the orifice has an almost equal effect on the oil film pressure in the inner and outer chambers.The oil film pressure in the outer chamber varies synchronously and periodically with the location of the outer ring,while the oil film pressure in the inner chamber becomes flattened under the influence of the deformation of the elastic ring.The steady-state oil film force increases squarely with decreasing oil film radius clearance at the same eccentricity,and also increases with increasing bearing speed at the same oil film radius clearance.The oil film force in the circumferential direction is about 1.5 times higher than that in the radial direction at the same eccentricity and oil film radius clearance.Therefore,significant damping effect is generated.The amplitude of the transient oil film force increases with the increase of bearing speed and rotor unbalance,but decreases with the increase of oil film radius clearance and squirrel cage stiffness.The circumferential oil film force is not significantly higher than the radial oil film force.3.A numerical method is proposed to analyze the dynamic response of displacement and velocity of ERSFD integrated ball bearings and reveals the effect of ERSFD structure and operating parameters on the dynamic characteristics of the bearings.The results show that:(1)The contact load and contact angle of the bearing tend to jump to zero and high frequency interference occurs when ERSFD is incorporated.This results in an increase in raceway friction and decrease in loadbearing stability.(2)When the oil film radius clearance increases from 0.4 mm to 0.7mm,the eccentricity and transmissibility for the ERSFD with bearings are decreased by 12.2% and 68.7% respectively.The corresponding values for the ERSFD without bearings are decreased by 27.5% and 68.8%.The radius of the center orbit of the inner ring is increased by a factor of 2.2 and a modulation frequency of 1/4 times the rotor speed appears.It was concluded that an increase in oil film radius clearance lowers the transmissibility,and therefore benefits to attenuate the bearing excitation,but makes the inner ring movement unstable.(3)As the squirrel cage stiffness increases from0.6855 to 0.8493,the eccentricity and transmissibility for the ERSFD including bearings are increased by a factor of 1.8 and 3 respectively.Correspondingly,the values for the ERSFD without bearings are increased by a factor of 1.7 and 2.7.An increase in squirrel cage stiffness is ineffective in attenuating the bearing excitation;(4)When the bearing speed increases from 8000 r/min to 14000 r/min,the eccentricity and transmissibility for the ERSFD with bearings are decreased by 28.6% and 54.6%respectively.The eccentricity remains unchanged and the transmissibility is decreased by 26.2% for the ERSFD without bearings.The center orbit sizes of the inner ring is increased by a factor of 1.5 and runs steadily,yet,as the speed increases further,its amplitude begins to oscillate.It was concluded that an appropriate increase in bearing speed enables to cut down the transmissibility of the outer ring and stabilize the movement of the inner ring.(5)When the rotor unbalance decreases by 32% and increases by 3.3 times relative to the steady state of the inner ring(U(28)0.25),the radius of the center orbit of the inner ring is decreased by 80.8% and increased by 1.08 times respectively.Too low or too high unbalance leads to an unstable movement for the inner ring.4.An ERSFD & Ball Bearing Dynamic Tester capable of variable speed,inertial loading and automatic temperature regulation was set up independently.The pressure distribution of the oil film in the outer chamber,the center orbit of inner and outer rings and the vibration of the outer ring were measured experimentally.The test shows that the oil film pressure in the outer chamber is distributed periodically with time.Its maximum amplitude is increased no more than 8% from 0.33 MPa as the rotor speed increases by 2.2 times from 6000 r/min.The outer ring center orbit evolves unsteadily when the rotor speed is lower than 9900 r/min,and the vibration acceleration oscillates between 6.1 g and 6.5 g with no decay.Once the speed is increased to 13000 r/min,both the inner and outer rings enjoy a steady motion and the bearing external excitation is attenuated by 18%.However,the amplitude of the inner ring increases.The model solution has a consistent trend with the experimental results,qualitatively verifying the correctness of the theoretical model.In this contribution,an ERSFD integrated inner and outer ring dynamic model directly oriented to the practical application of aero-engine main bearings was established,and bearing dynamics characteristics analysis and experimental research were carried out.The research findings contribute to understanding of the nonlinear characteristics of the bearing supports and help the design,dynamic analysis and engineering application of ERSFD integrated ball bearing systems.