Towards accurate numerical fluid dynamics of pump-turbine runners in deep partial load operation

Abstract

The operation of pumped storage power plants at off-design conditions requires an understanding of the flow field and the resulting damage to ensure a safe and economic operation. Within this study, CFD simulations are carried out for an existing pump-turbine at deep part load operation to enable calculating the damage in later structural analyses. Furthermore, this study includes the comparison between the SST and SBES turbulence model at different mesh sizes. The simulation results are compared with model test data regarding head, torque and pressure fluctuations at a bottom ring and draft tube cone sensor. Whereas all simulation setups are within a reasonable range to the available model test data, the pressure fluctuations on the runner blades as well as the resolved vortices within the runner blade channels show a qualitative difference between both models. The SBES turbulence model resolves more vortices and thus different pressure fluctuations. Subsequent structural analyses show higher accuracy of the SBES turbulence model compared with the SST model. A mesh refinement from 25 million nodes to 80 million nodes with the SBES model reveals a better resolution of vortices, but only local differences in pressure fluctuations.