Theoretical Estimates of Rotordynamic Fluid Forces on a Front Shroud of Francis Turbine Caused by Leakage Flow

抄録

The rotordynamic fluid forces on a columnar rotor modeling the front shroud of Francis turbine caused by the leakage flow and whirling motion are evaluated by the experiments and the computations, to explain the self-excited vibration observed in free vibration tests. In addition to the leakage flow models previously proposed, a new model is proposed to include the effects of the rotation and whirling motion of the rotor to evaluate the rotordynamic fluid forces. After checking the validity of the models by comparisons with experiments and CFD, the characters of each component are discussed based on the physical mechanism producing the forces. It was found that the rotordynamic force component normal to the whirling orbit is mainly caused by the centrifugal forces of the added mass of the fluid in the clearance and that the tangential force is mainly caused by the acceleration of the axial leakage flow through the clearance.