During their lifetime wind turbine blades are exposed to highly dynamic loads, resulting from cyclic changes in gravity direction, centrifugal forces and changing wind conditions such as average wind speed, turbulence intensity, rapidly changing wind direction, wind shear, extreme wind gusts and site-specific loads like e.g. wake effects from neighbouring wind turbines.
Throughout the project BLATIGUE, supported by EUDP and Villumfonden, the partners are developing more efficient fatigue testing methods for large wind turbine blades. The project is also developing equipment to excite the blades under such tests.
Need for new testing methods
Most of the fatigue testing today is carried out by dividing the fatigue loads, calculated in aeroelastic simulations, into two principal components; in flapwise and edgewise directions. Some attempts to combine the flap- and edgewise loads into a single fatigue test have been carried out, but we need to take it a step further.
“The standard certification tests used to test wind turbine blades today are not representing the real world. Blades are exposed to torsion and bending in different directions at the same time, which is not reflected in the standard today. The industry consequently needs fatigue test methods that better match the loads to which the blades are exposed in real operational conditions. The fatigue test methods we are developing in the BLATIGUE project do exactly that,” says Kim Branner, Senior Researcher at DTU Wind Energy and responsible for the BLATIGUE project.
Bringing new blades in the market
Rasmus Ladevig, Head of Blade Test at Siemens Gamesa, is part of the BLATIGUE project. At Siemens Gamesa they see the need for more focus on testing of wind turbine blades:
“As a wind turbine supplier, we typically focus on “the next blade”. In a market where size matters and where especially our ability to launch products timely in the market is key, we are typically under heavy time pressure when the next big blade arrives in our test facility. As last of the process of bringing new blades in the market, we must often counteract the delays seen in design and prototype manufacturing,” he says and continues:
“In the BLATIGUE project, we can focus on collaborating with researchers from an established and worldwide known group of wind energy researchers and ensure delivery of results at a more suitable pace for development. By having another blade test supplier in the project, we are certain that we are challenged on “how we normally do things” and with a certifying body present, we can ensure that what we develop will be recognized in the industry. In addition, we even have a major wind turbine customer present to underline the necessity of more quality in blade testing.”