Cavitation in the U9-400 Kaplan turbine model at BEP and PL conditions near cavitation breakdown

Paper in proceeding, 2025

This study employs highly resolved CFD to analyze cavitation near cavitation breakdown in a Kaplan turbine model known as U9-400. Both BEP (Best Efficiency Point) and PL (Part-Load) conditions are examined. A comparison is made with data from experiments, provided by Vattenfall, which include high-speed camera recordings of cavitation regions between the blades, and the associated efficiency loss caused by cavitation breakdown. It is shown that the numerical results successfully replicate the experimentally observed cavitation and accurately predict the efficiency reduction. Additionally, we explore the underlying causes of the efficiency reduction near cavitation breakdown, identifying it as a consequence of the diminished pressure difference between the suction and pressure sides of the runner blades.