| The dynamic characteristics of the rotor system are not only related to its own structure,mass distribution and other parameters,but also influenced by the support stiffness and sealing.Therefore,this paper analyzes the dynamic characteristics of the rotor system of the high-speed seal test bench considering the influence of bearing stiffness and fingertip seal.According to the mechanical model of rolling bearing,the horizontal and vertical bearing stiffnesses are solved;according to the structure and working principle of fingertip seal,the equivalent mechanical model of fingertip seal-rotor is established,and the seal stiffness and sealing force are solved.The dynamic characteristics of the rotor system are analyzed using finite element software,and the effects of bearing stiffness and fingertip seal on the dynamic characteristics of the rotor system at different positions are investigated.Finally,vibration test experiments were designed based on the high-speed seal test bench to verify the accuracy of the finite element calculations.The main research contents and conclusions are as follows:1)The differential equations of rotor system dynamics and the mechanical and stiffness models of rolling bearings considering the anisotropy of bearing stiffness are established,and the dynamics equations of the rotor system are solved by Matlab,and the radial runout of its center of mass and the swing angle are obtained.The results show that the stiffness of the rolling bearing differs in horizontal and vertical directions and has variable characteristics,so the average stiffness of the rolling bearing is taken for calculation,and the stiffness of cylindrical roller bearing and angular contact ball bearing are 79.52 N/μm and 6.85 N/μm in vertical direction and 13.4N/μm and 1.99N/μm in horizontal direction respectively.When the speed of the rotor is 9000r/min,the maximum amplitude and swing angle of its center of mass are 13.7×10-6m and 10.01x10-3° in the horizontal direction and 2.85×10-6m and 6.80x10-3° in the vertical direction,respectively,and the amplitude and swing angle of the rotor system in the horizontal direction are greater than those in the vertical direction.2)According to the working principle and characteristics of fingertip seal,a mechanical model of fingertip seal-rotor interaction is established,and the methods for solving the contact stiffness between fingertip boot and rotor surface in contact area,the air film stiffness between fingertip boot and rotor surface in non-contact area,and the equivalent structural stiffness of fingertip beam are summarized.The fingertip sealing force calculation equation is derived according to the mechanical model,and finally the time-varying sealing force calculation equation is derived in the global coordinate system XOY considering the variation of the sealing force with time.3)The critical speeds of the rotor system were obtained by the finite element method from 3000r/min to 21000r/min,where the first-order forward and reverse critical speeds were 10655r/min and 10454r/min,and the second-order forward and reverse critical speeds were 19760r/min and 18143r/min,respectively.The modal vibration patterns of the rotor system were compared,and it was found that the modal vibration patterns of both orders showed bowing bending,and the maximum displacement was at the cantilever end of the rotor.Considering only the unbalanced mass of the runway,the unbalanced response of the rotor rotational frequency in the range of 5-35 0Hz was analyzed,and it was found that there were two abrupt changes in the unbalanced response amplitude and phase,which appeared at 170.6Hz and 298.3Hz respectively.The influence of the change of bearing stiffness at different positions on the critical rotor system speed and modal vibration pattern was analyzed,and it was found that with the increase of bearing stiffness at different positions,the critical rotor system speed increased to different degrees.Finally,the influence of the fingertip seal on the dynamic characteristics of the rotor system was considered,and the critical speed,vibration pattern and unbalance response of the rotor with and without the fingertip seal were compared,and it was found that the critical speed of the rotor system increased significantly and the deformation decreased under the influence of the fingertip seal,and the critical speed of the rotor system continued to increase and the deformation continued to decrease with the increase of the fingertip seal stiffness.4)The software and hardware of the high-speed seal test bench and vibration signal acquisition system are introduced and a test protocol is developed.The vibration signals at the angular contact ball bearing of the rotor system with and without the influence of the fingertip seal were obtained in the rotational frequency of 50Hz-229Hz.It was found that the vibration acceleration in the horizontal direction of the rotor system at the angular contact ball bearing was greater than that in the vertical direction,and the horizontal vibration acceleration at one frequency always dominated,while the vibration acceleration in the vertical direction had a multifrequency component.Analysis of the vibration signal of the rotor system with and without the fingertip seal shows that the critical rotor speed and vibration acceleration increase under the action of the fingertip seal.According to the rotor frequency-doubling frequency amplitude curve,the first-order critical speed of the rotor system with and without the fingertip seal is 11,850r/min and 10300r/min respectively,and the error is within 4%compared with the first-order critical speed obtained from the finite element analysis,which verifies the reliability of the finite element method. |
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