Cavitation as a limiting factor for the empowering of a Kaplan turbine – CFD calculations, test rig results and operational experience

The Krippau run-of-river hydropower plant is revitalized, and for this purpose, a new runner was developed. The 24 MW power plant was commissioned in 1965 and is equipped with only one unit. The refurbishment aims at an increase of the efficiency in the relevant operating range of the turbine through a runner replacement (while maintaining the runner diameter). Furthermore, the maximum discharge shall be increased from 120 m³/s to 135 m³/s and the annual production by 4% The new design of the runner with a diameter of D = 4.1 m was developed using computational fluid dynamics simulations and finally checked by a model test according to IEC 60193. Due to given plant sigma values, which generally do not allow for such an extension in the operation range, the particular focus lay on cavitation performance, as it was a big challenge to achieve acceptable cavitation characteristics.