Mode Shift of Twinborn Blades of Steam Turbine
Governing Stages
Xu Zili1,Pan Yongyue2,Xiao Changjiang2,Xiao Hui2
(1.School of Energy and Power Engineering,Xi'an Jiaotong University, Xi'an 710049,China;
2.Steam Turbine Institute,China Chang Jiang Energy Corporation,Wuhan 430074,China; )
Abstract:Vibratory characteristics of twinborn blades of the governing stage for one 50
MW steam turbine were studied using the finite element method.In the finite element model
the three dimensional incompatible element with 8 nodes was employed. When the steam
turbine is in operation,high temperature and the centrifugal force cause the increase of
the rim diameter of disk,give rise to the matching surfaces of roots of adjoining blades
loosing, and dovetail parts over radial supporting surfaces taking part in blade
vibration. The calculated results show that not only the natural frequency of blades in
operating is smaller than the counterparts in stationary but also the modal order of the
blade shifts when the blade runs from the stationary to the operating states. In
stationary, the first mode is the tangential vibration of blade,and the second mode is the
axial vibration.In operating, however, the first mode turns from the tangential vibration
mode into the axial vibration mode,and the second mode translates from the axial vibration
mode into the tangential vibration mode.
Keywords:steam turbine; governing stage;twinborn blades;vibration;finite element method