Effects of load reduction on forces and moments on the runner blades of a Kaplan turbine model

Abstract Today’s electric energy system includes more renewable sources than ever before, with a large increase in wind and solar power. The intermittency of wind and solar power brings certain challenges in maintaining the balance of the electric grid. Hydropower has shown great potential in solving the grid balancing problem. However, historically hydropower has had a completely different role, covering only the base load. The water turbines were designed to operate at the best efficiency point for most of their lifetime, and other kinds of operation may cause unpredictable shortening of the lifetime of the machines. Safe operation and planned maintenance are of great importance for both continuous energy distribution and human safety. In order to use the potential of hydropower to operate with highly variable loads, more comprehensive studies need to be made on the effects of transient operation of water turbines. An extensive series of studies have been made in recent years on the transient operation of Francis turbines and pump turbines. However, transient operations of Kaplan turbines require more in-depth studies. The present work analyses the flow-induced forces and resulting torques and bending moments on the U9-400 Kaplan turbine model runner blades during a load reduction sequence. New implementations in the OpenFOAM open-source CFD code have been developed to extract the forces, torques and bending moments on individual blades with respect to coordinate systems rotating with each individual blade.