Study On The Experimental Identification Method Of Oil Film Dynamic Characteristics Coefficients Of Squeeze Film Damper

Squeeze film damper(SFD)is widely used in aircraft engine.SFD is used in reducing the vibration amplitude of rotor system and the transmission of vibration from the rotor system to the casing,which has important significance to reduce the engine vibration and to increase machine life.Dynamic characteristic coefficients of SFD are important parameters affecting the vibration characteristic of aeroengine rotor support system.However,the influence rule of structural parameters and physical property parameters on the dynamic characteristic coefficients of SFD is still unknown,so trial and error by theoretical and experimental methods are still needed in SFD design.Therefore,it is necessary to build a SFD dynamic characteristic identification test rig to conduct experimental research.Firstly,the frequency domain identifying method on dynamic characteristic coefficients of SFD is analyzed.The dynamic model of the test rig is established.The calculating method of dynamic characteristic coefficients based on this test rig is given.Secondly,in order to solve the problem of inaccurate signal features caused by spectrum leakage after Fast Fourier Transform(FFT),a signal feature extraction method based on FFT and least square method is proposed.It can accurately identify the signal characteristics of periodic signal and effectively reduce the error of experimental calculation.Thirdly,the dynamic characteristics of the cross spring system are discussed.When the main shaft is whirling within the oil film radius clearance,the stiffness of the system is approximately constant,but the preload of spring affects the stiffness of the system.Then the dynamic model of the test rig is established,in which the vibration of test rig support is considered.The amplitude/phase frequency characteristics are calculated,the precision of different formulas calculating dynamic characteristic coefficients is discussed.When the vibration of test rig support cannot be ignored,the absolute acceleration measured by acceleration sensor should be substituted into the equation for calculation.The method proposed in this paper is of high precision.Finally,the test rig for identifying dynamic characteristic of SFD is designed and built.The composition and function of each system of the test rig is described.The regularity of dynamic characteristic coefficient changing with whirling frequency is studied.It is found that the damping coefficient of the oil film does not change with the whirling frequency,which proves that the test rig is reliable in identifying the dynamic characteristic coefficient of SFD.The research results of this paper lay a foundation for further exploring the variation law of dynamic characteristic coefficients of SFD and for studying the optimal design of SFD-rotor system in aero engine.