In the past two decades, the installation of more and more Renewable energy sources in Europe has forced hydraulic turbines to operate under critical conditions. This demand for extended offdesign operation brings many new challenges to the design and even more to old turbines. Flow-induced forces lead to forced excitation frequencies that have to be understood and taken into account when estimating the runner load curve for lifetime prediction. To attain a reliable and safe runner design, understanding of different flow-induced excitations coming from pressure pulsations and the resulting structural response is important.

In the past four years the institute researched some of these effects at prototype Francis turbines and the structural response. Numerical approaches were validated with site measurements. The focus of this paper will be related to fluid-structure interactions at different load steps. Most interesting topic in this matter is that not all appearing phenomena have the same contribution to the load curve of the turbine. Investigating also two runners with varying specific speed show different behavior. Used methods at the research project will be discussed and where possible, we will compare calculation results versus measurements.