Hits:

Indexed by:会议论文

Date of Publication:2010-01-01

Included Journals:CPCI-S

Page Number:1087-1095

Abstract:Severe flexural vibration of the rotor shaft of a Francis turbine runner was experienced. It was shown that the vibration was caused by the fluid forces and moments acting on the backshroud of the runner associated with the leakage flow through the back chamber. The motion of a rotor on a vibrating shaft can be divided into two fundamental modes. One is whirling motion with a lateral linear displacement, and the other is precession motion with an angular displacement. The fundamental characteristics of rotordynamic fluid force moments on the backshroud of a Francis turbine runner in the whirling and precession motions were studied by model tests and the computations based on a bulk flow model, respectively. The effects of the leakage flow rate, the preswirl velocity at the inlet of the radial clearance, and the axial clearance on the fluid force moments were examined. It was found that, in the whirling motion, the fluid force moments have a destabilizing effect in wide regions except for a small region with positive whirling angular velocity ratios. On the other hand, in the case of the precession motion without the rotation of the disk, the normal moment did not have the effect of encouraging the precession motion; in the case of precession motion with the rotation of the disk, the normal moment destabilizes the precession motion in a small region with positive precession angular velocity ratios. The swirl flow due to the rotation of the disk was found to be responsible for the encouragement of the precession motion.