Proposal of simplified model for improved prediction of bending mode vibration of stepped rotor

Takada, Shoji; Funatake, Yoshio; Inagaki, Yoshiyuki

The design of gas turbine high temperature gas cooled Reactor with a power output of 300 MWe employed magnetic bearings for supporting gas turbine rotor composed of turbo-compressor and generator rotors, which are connected by a flexible coupling each other. The generator rotor is a flexible rotor, which passes over the forth critical speed below the rated speed. The total length, mass and rated speed of the rotor is 18 m, 67 t and 3600 rpm, respectively. A simplified rotor-dynamics model was proposed based on Timoschenko beam model by adding a rotational spring which simulated deformation of plane at stepped parts of rotor. The model predicted adequately the bearing stiffness dependency on vibration mode of rotor at critical speeds in comparison with those 3D FEM analysis, as well as the increase of inclination at the center of rotor where mass was concentrated because bending stiffness, which affects whirling motion by Jayro effect at the forth critical speed.