Theoretical And Experimental Research On Dynamics Of Two Phase Flow Squeeze Film Damper-Rotor System

Turbomachinery,such as bumps,compressors and turbines,is widely used in many kinds of rotating machinery.In modern turbomachinery system,rotor usually runs over the first critical speed or even higher.Rotor vibrates fiercely when approaching critical speeds,and the interaction between rotor and supporting part becomes strong as well,which leads to the rubbing,fatigue and breakdown.Squeeze film dampers(SFDs)and elastic ring squeeze film dampers(ERSFDs)are applied in rotor systems to suppress the vibration when traversting the critical speed,because of the simple structure and damping effect.However,SFD damping effect can be influenced by various factors,two-phase flow resulting from cavitation or air ingestion is the one that weakens the damping coefficient of SFD.Besides,the dynamics of a two-phase flow lubricated SFD is excitation and supply pressure dependent.It is important to investigate the influence of two-phase flow to the dynamics of SFD and rotor system.Based on the pratical operating condtion of aero-engine,this dissertation investigates the dynamical characteristics of both SFD and rotor system,under the influence of two-phase flow.Both numerical simulation results and experimental results are presented,which can be summarized as follows:(1)The dynamics of a two phase flow SFD is investigated through numerical simulations.The regions of air ingestion,oil film pressure and oil film coeffieicents with different eccentricities are analyzed using volume of fluid(VOF)method.On the other hand,a homogeneous model is introduced based on Rayleigh-Plesset equation,and analyze two-phase flow effect on SFD oil film pressure and oil film coefficients.(2)The dynamics of a SFD lubricated by bubbly mixture under extreme low oil supply pressure is investigated by pratical experiments.Oil film coefficients for unidirectional and pulsed excitation tests are obtained,when the SFD is lubricated by air in oil mixture and the oil supply pressure is extremely low.Moreover,experimental results for large oil supply pressure are also obtained to compare with the low supply pressure results.Pictures of SFD oil film clearance are displayed to illustrate the process of air ingestion.In addition,low frequency vibration is revealed.(3)The influence of two-phase flow on the dynamics of rotor system is studied.A SFD-rotor system is established,considering laterial and pitching vibration.Resonant responses,as well as the bifurcation phenomenon,for different imbalances and gas volume fractions(GVFs)are calculated.(4)Tests are carried out on a SFD-rotor test rig to validate the numerical simulation results.Bases on the practical operating condition,a SFD-rotor test rig is built.The vibration signals for different imbalances and GVFs are recorded.Frequency amplitude spectras during the speeding up process are abtained to compare with numerical results.Besides,super-harmonic resonance and bifurcation are revealed,as well as the low frequency vibration.(5)The damping characteristic of ERSFD is analyzed.A ERSFD-rotor dynamic model is established,a whirling period of rotor is divided into ten time steps,oil film pressures,oil film coefficients and the contact conditions in the oil chamber at each moment are calculated,corporating with finite element method.The damping mechanism of ERSFD and the effect of elastic ring are discussed.