Research On The Dynamic Characteristics Of Elastic Ring Squeeze Film Damper

SFD has been widely used in aero engine as well as industrial turbine due to its simple structure and high reliability.To relieve the nonlinearity of conventional SFD film,Russian researchers proposed elastic ring squeeze film damper(ERSFD)by locating elastic ring inside the film gap of SFD.As a novel SFD ERSFD is quite promising because it is able to adjust the natural frequency of the system as well as attenuate vibration with smaller size.Up to now the relevant investigations are scant,in particular the lack of prediction and identification of its force coefficients makes it hard for engineers to assess and design ERSFD.According to the geometric feature of ERSFD,analytical solutions to the film pressure of inner and outer film based on short bearing assumption are presented in this paper.The inner and outer film pressure profiles and film forces are investigated.Based on that the film force coefficients obtained and discussed;the numerical model of ERSFD by fluid-structure interaction approach including cavitation effect has been proposed and the influence of cavitation on film force coefficients is investigated.Since for conventional method the film force coefficients are identified utilizing inner film force only,the numerical model of ERSFD with contact model is proposed.Based on that a more reasonable approach is presented to obtain the force coefficients of ERSFD.One step further,the test rig for the force coefficients identification of ERSFD is established and the numerical predictions are verified by experimental data.The experiments to test the dynamic characteristics of ERSFD-rotor system are conducted as well to provide necessary materials for the design and application of ERSFD.To obtain the film forces of ERSFD by numerical method is complex and extremely time-consuming,which makes it difficult to analyze the dynamic characteristic of ERSFD-rotor system.In response to this issue the analytical solutions to the inner and outer film pressure are proposed based on the hypothesis that high vibration mode can be neglected as well as short bearing assumption.Comparisons between analytical solution and numerical results indicate that the proposed solution is available when length-diameter-ratio is below 0.5,thickness of elastic ring is above 1mm and whirling frequency is smaller than 200 Hz.The characteristics of inner and outer film forces are investigated and specified components related boss number N are observed on the frequency spectrums of film forces.Existing boundary conditions for ERSFD are not reasonable therefore obta ined results are in doubt.In response to this problem,a more reasonable numerical model for ERSFD is proposed based on Reynolds equation and kinetic equation of elastic ring.The coupled governing equations are solved by block-iterative method.The film force coefficients of ERSFD are obtained and compared with SFD.The results indicate that the film force coefficients of ERSFD are constant in a wider range of whirling radius ? compared with SFD.The thickness of the elastic ring has slight influence on the film damping and inertia coefficients but decreasing the thickness of the elastic ring can significantly reduce the film stiffness while operating at high whirling frequency.The film force coefficients increase first then decrease with the increase of boss number N and boss width WB.As ERSFD with two layers of film are more vulnerable to cavitation,the numerical model of ERSFD by fluid-structure interaction approach including cavitation effect is proposed based on Zwart-Gerber-Belamri model.The influence of cavitation on film force coefficients is investigated compared with non-cavitated approach.The results reveal that cavitation mainly takes place in inner film of ERSFD and lead to a significant decrease of film damping coefficient and an increase of film dynamic stiffness coefficient.Moreover the decreased part of film damping coefficient due to cavitation is proportional to the air volume fraction of inner film.The film force coefficients of ERSFD are obtained by processing time-domain inner film force only according to existing method.In response to this drawback the numerical model of ERSFD including contact is proposed based on Greenwood-Williamson model and a more convincing approach is presented to obtain the force coefficients of ERSFD.The improved method is validated by experimental data.The film damping coefficient drops with the increase of c1 as well as c2,which indicates that ignoring the contact mechanism on the boss would underestimate the influence of outer film on the film force coefficients.The non-dimensional ratio of film damping coefficient to film stiffness coefficient ?K reaches minimum around the region that c1=c2.The test rig for the force coefficients identification of ERSFD is established,the influence of whirling radius,feeding pressure as well as inner and outer film clearances on the force coefficients of ERSFD are investigated experimentally.In addition the ERSFD-rotor test rig is set up and the vibration attenuation ability of ERSFD is validated on the rotor system.In addition the attenuation ability of ERSFD is enhanced under larger feeding pressure and larger vibration amplitude.