Analysis of Pressure Fluctuation of a Pump-Turbine with Splitter Blades on Small Opening in Turbine Mode

Unstable flow in a pump-turbine can cause pressure pulsation, and the resulting vibration deteriorates the stability and operating safety of the unit. This study conducted three-dimensional numerical calculations of the overall flow passage of a pump-turbine with splitter blades under the small guide vane opening, and the unsteady flow characteristics of the turbine were investigated. The results showed that the pressure fluctuation was more severe at lower head operating conditions with lower efficiency, especially in the vaneless area (the runner blade passages). Under the lower head condition, the proportion of 12 times the rotational frequency (12 f/fn) increased in the vaneless area, and the amplitude of 1 f/fn as well as 2 f/fn became larger in the runner blade channel, with more space occupied by vortices and reflux areas. A spiral vortex rope formed in the draft tube, increasing the proportion of 0.4 f/fn and 0.7 f/fn pressure pulses.