Challenges with onboard strain measurements on a model Francis turbine runner

Abstract

As the world transitions towards more renewable energy sources, as a step to reduce the emissions of CO2, intermittent and non-dispatchable sources like solar and wind will take up a larger proportion of the energy production. With more unregulated power in the energy mix, a higher demand is put on the rest of the energy production system. Hydropower is in a unique position as it is both renewable and a highly flexible energy source. The increased use of flexible operation of Francis turbines especially, puts a higher dynamic load on the runner components which as a consequence leads to a reduced lifetime. In this paper we present the experimental setup and results from a measurement campaign performed on a model of a low specific speed Francis runner. Onboard measurements with strain gauges at the trailing edge of two runner blades were performed. The experiments were conducted as a part of the HydroFlex project with the goal of validating numerical simulations and to gain a better understanding of the reduction of lifetime on Francis turbines due to higher fatigue loading from more flexible operation. The results shows that there were a significant drift of the mean strain over time during the measurement campaign, and a lower measured strain at BEP than expected when compared to numerical simulations. In this paper, the experimental setup, results and challenges encountered are presented.