Dynamic Radial Forces and Pressure Fluctuations Measurement at Off-Design Conditions on a Model Scale Pump-Turbine

Abstract

The main challenge in the pump-turbines development are hydraulic instabilities in the partial loads in both pumping and generating mode. For the mechanical design of the pump-turbine shaft and bearings, it is necessary to know the magnitude of the dynamic radial forces caused by these instabilities. The radial force magnitude is usually determined on the basis of head and the runner dimensions. The paper focuses on the comparison of the empirical approach to the radial forces and the measurement on the model scale pump-turbine that was carried out in the Litostroj Engineering hydraulic laboratory in Blansko, Czech Republic. There were six strain gauges mounted on the bearing support to monitor the radial forces. In the pumping mode two distributor openings were measured. In the generating mode eight distributor openings were measured with the focus on the S-shaped curves region in the characteristic. Additionally, there were pressure gauges installed in the vaneless gap between the distributor and the runner to monitor the pressure fluctuation and potential presence of rotating stall. The appearance of rotating stall was connected to the magnitude of dynamic radial force.