The demand for flexible hydropower to stabilise electricity grids is growing worldwide.

In Germany, hydroelectric power plants will also increasingly be used in future to stabilise electricity grids as a result of the ever increasing share of renewable energies such as solar and wind power. As a result, the requirements placed on hydropower plants are also changing.

Frequent load changes, long running times at low outputs and repeated start-ups and shut-downs are placing not only greater demands on the water turbines than before but also new demands on the material. The collaborative FrancisPLUS project is aiming to further increase the efficiency of Francis turbines, which are used in numerous hydropower plants, in collaboration with science and industry.

Optimised blade design for more efficient turbines

The behaviour of the Francis turbine in the partial load range is being researched in order to enable the turbines to be also used outside the normal operating range, close to the optimum, while at the same time achieving a high efficiency, long service life and smooth running. One of the goals is to achieve an optimised blade design that enables the safe, reliable and economical operation of the turbines. For this purpose, vibrations, pressure fluctuations, efficiencies, cavitation and the service life are being investigated. By making a direct comparison between the model test and the large-scale plant, the phenomena investigated on the model can be transferred directly into practice.

Two further subprojects deal with the flow simulation and materials science. There, research is being carried out into how the dynamic load, i.e. the time-dependent pressure distribution, impacts on the turbine blades in order to determine the operational strength on the basis of the data. In addition, fatigue strength values are being determined for the blade material. A focus here is on investigating the material fatigue in the low-cycle range, as this is increasingly being used due to the flexible use of turbines. Based on the results, it is intended to develop methods for increasing the service life of Francis turbines for plant constructors and operators.