Influences of Clearance in the Nether Wearing Ring on the Self-Excited Vibration of the Francis Turbine

Aimed at the self-excited vibration of caused by unreasonable clearance in wearing ring of the Francis turbine, whole flow passage of prototype hydraulic turbine which contains the clearance in wearing ring is numerically calculated by computational fluid dynamics software CFX based on N-S equation and RNG k-turbulence model. The result shows that the flow field in front of inlet of runner is unstable extremely, even if a tiny disturbance effects on, which will be out-of-balance symmetrically in the radial direction, then the force of runner will be unbalance, which will cause vibration of the hydraulic turbine. As well as, a reasonable clearance in wearing ring of the Francis turbine will reduce the impact of the water in the inlet of the clearance, and self-excited vibration of the hydraulic turbine will eliminate.