Research On Modeling Method And Dynamic Characteristic Analysis For Squeeze Film Damper Rotor System

To pursue high performance and high reliability,co-and-counter rotating dual rotor system,squeeze film damper and intermediate bearing are widely applied in modern aeroengines.Although these technologies are advantageous in improving aeroengine's performance,they also exacerbate the vibration coupling between high and low pressure rotors,making the rotor system more complex in dynamic characteristics.Therefore,it's urged that the dynamic characteristics of the rotor system should be predicted more accurately,so as to avoid disadvantages of these new technologies while retaining the advantages to ensure safe,reliable and smooth operation of the aeroengines.In this paper,studies are conducted to investigate modeling method and nonlinear dynamic characteristics for complex rotor systems of aeroengines.The main contents and innovations of this paper are listed as follows:(1)A modeling method for complex rotor system is developed by combining the finite element method and different model reduction methods.The mass matrix,stiffness matrix and gyroscopic matrix of the rotor system are obtained by the finite element model established with Timoshenko beam theory.Then different model reduction techniques are applied to reduce dimensions of the problem.Besides,two methods to obtain critical speeds of the rotor system,the Campbell diagram method and the direct method,are compared and analyzed.The direct method is applied to a dual-rotor system for analyzing the critical speeds differences between co-and-counter rotating dual-systems.Numerical results show that the fixed interface modal synthesis method is advantageous in both accuracy and efficiency comparing with other model reduction techniques.Although the Campbell diagram method has almost the same accuracy with the direct method,it is much more time consuming.Research stated above show that the combination of the finite element method and the fixed interface modal synthesis method can be efficiently applied to establish model of the complex rotor system while retaining the accuracy.Thus it is of great engineering value.Besides,the direct method is much more efficient in evaluating critical speeds of the rotor system so that the design cycle can be shortened.(2)Combinging the finite element method and the fixed interface modal synthesis method,an efficient modeling method is developed to study nonlinear dynamic characteristics of a dual-rotor system fitted with squeeze film damper and intermediate bearing.Then nonlinear dynamic characteristics of the dual-rotor system is studied to reveal the influence of speed ratio.This methodology is of great engineering value and theoretical significance.(3)The nonlinear dynamic characteristics of an industrial turbine engine fitted with squeeze film dampers and elastic supports are investigated with and without static eccentricity of the SFD.By comparing the results it is concluded that: periodicity of the dynamic response for the rotor system can be influenced by the static eccentricity of the SFD;static runout and super harmonics can be observed for rotor system with static eccentric SFD;the static sprung eccentricity would make the center of the orbit of the journal offset from the center of the SFD and thus to make the SFD inefficient/ineffective.These conclusions imply that counter measures must be applied to prevent static sprung eccentricity thus to guarantee safe,reliable and smooth operation of the rotor system.(4)A frequency domain technique based on receptance harmonic balance method and finite element method has been devised to overcome weakness of the time domain method presented in previous chapters.The frequency domain technique is applied to a dual-rotor system with floating ring squeeze film dampers and intermediate bearing.Numerical simulations show that: the maxium vibration amplitude of disks is observed around the intermediate bearing,corresponding to the high/low pressure tubine disks of actual aeroengines;the maxium amplitude can be greatly reduced by lowering the stiffness and radial clearance of FSFD for supports around the intermediate bearing,especially for the aft support of the inner rotor;the blade loss test rig was design and the experimental results show that transient response process exerted by blade loss can be greatly suppressed by the floating ring squeeze film dampers.This method has important theoretical significance and engineering application value in providing an efficient frequency domain method to study dynamic characteristics of the complex rotor system.The investigations conducted in this paper provide efficient modeling method and foundation for nonlinear dynamic characteristics investigation of complex rotor systems.The results are of significant theoretical and engineering value for designing the complex rotor system.