Pressure Pulsations and Fatigue Loads in High Head Francis Turbines

The Norwegian power system today includes a relatively large percentage of Francis turbines with a head of above 300m, in the world. This leads to a need to maintain and develop the national competence regarding the challenges connected to this type of turbine. The importance of this competence is increased by the fact that these turbines have a high installed capacity and are therefore crucial to the production stability. In the later years the old runners in Norwegian high head power plants have begun to show signs of fatigue. Taking the average age of these runners, which is approaching 45 years, into account, this may not be surprising. The surprising fact is that the same signs of fatigue, and in some cases total breakdown due to cracks, also occur in new and modern Francis runners. This leads to a hypothesis that the problem stems from sources other than the turbine runners themselves. The suspected cause of this reduction in the expected lifetime is the change the pattern of turbine operation to accommodate new intermittent energy in the power system and progress in the manufacturing technology enabling thinner blades. As an example the Horizon2020 project HydroFLEX initialised by the European Union aim to produce technology that allows for 30 start-stops per day for Francis runner. A research project funded by the Norwegian Research Council and the Norwegian Hydro Power Industry, aim to increase the available knowledge regarding these high head Francis turbines. The research is done both on a basic and applied level where the focus is to increase the knowledge of the phenomena and to produce validation data for numerical simulations of said phenomena. The fundamental research focus on the hydrodynamic dampening applied on a hydrofoil within a high velocity water flow. The applied research is focused on the Francis-99 runner, a model runner of a High Head Francis turbine, which has been instrumented in order to study the Rotor-Stator-Interaction(RSI) and the structural response of the runner. The research areas both consist experimental and numerical studies, where the experimental results are used to validate the numerical. This paper presents the background of the project, the different activities and some preliminary results from selected activities. The aim of the paper is to introduce the project, participants and the participants view on the future of High Head Francis runners that do not crack due to RSI