Fraunhofer Institute for Wind Energy SystemsAt a glance
- Over their service life of 20–25 years, rotor blades are subjected to high loads which can occur in the edgewise and flapwise directions simultaneously.
- Conventional testing methods are not capable of reproducing these combined loads.
- Fraunhofer IWES has already succeeded in applying elliptical biaxial loading to the rotor blades in a demonstration test.
- The project partners are now further developing this approach in the SmarTestBlade research project with the aim of rendering the method usable for type tests.
- In a subproject, the project coordinator, Fraunhofer IWES, is responsible for the further development of the test methodology.
The challenge
Rotor blades are among the most highly loaded components in a wind turbine. Over the course of 20–25 years, the loads from the wind and the component’s own weight affect the structure. The rapid increase in the size of turbines in recent years and the ever-greater requirements for safeguarding against failure have made reliable testing and validation methods for rotor blades particularly important.
Rotor blades are usually subjected to loading in the edgewise and flapwise directions separately during the type testing in order to check their fatigue resistance. In operation, however, the blades are also loaded in combined directions.
The solution
Elliptical biaxial rotor blade tests combine the fatigue tests in the edgewise and flapwise directions in a single validation test and permit the application of realistic loads. This increases the validity and quality of the experimental validation and reduces uncertainties in the design. However, the methods cannot yet be mastered on the required scale and do not have the necessary degree of maturity for type certification.
The aim of the SmarTestBlade research project is therefore to further develop and validate methods for the realistic validation of rotor blades utilizing elliptical biaxial testing. This will result in a method corresponding to the requirements of a type test.
The added value
In a subproject, the project coordinator, Fraunhofer IWES, is responsible for the further development of the test methodology. In a previous demonstration test at IWES, we verified the controllability of the load introduction during elliptical biaxial excitation of the rotor blade. The test methods are now to be refined for stability and further questions which arose from the demonstration test shall be answered in order to render the test method ready for use.
