‘Shark fins’, ‘winglets’ and ‘turbulators’ all refer to types of tip designs for wind turbine blades—part of an innovative research project called ‘InnoTip.’ The blade tip is the primary source for noise, loads and power output from a wind turbine, so there are significant potential gains from further optimising this part of the blade.
With the ultimate goal of reducing the levelised cost of energy (LCoE) through optimised tip design, the InnoTip research project started as a collaboration between LM Wind Power’s aerodynamics team and TNO. During this project three new tip designs were delivered and two were tested by extending blades with a temporary add-on tip extension—a unique process.
The project showed that power increase from the new tip designs was even better than expected—up to six percent in the initial tests—proving that these new geometries as well as the field tests were successful.
By using the insights TNO gained new avenues for changing the design of the blades to improve output and efficiency without necessarily changing the structural design or production processes. We have included this knowledge as part of new blade developments and look forward to bringing even better performing blades to market. Extending blades with an add-on tip and removing them without damaging the original blade is nerve-wracking, as many things can go wrong, but we proved the feasibility and gained invaluable knowledge.
Designing the optimal blade tip
The InnoTip project aimed to design and demonstrate three innovative tips targeted for offshore wind farms. Turbines offshore are less constrained by noise limitations, so there is the potential for designing tips more effectively.
The goal with the InnoTip designs was to increase the Annual Energy Production (AEP) of an offshore wind farm by two percent. Considering that one offshore wind turbine with 88.4 meter blades can power 10,000 households, even a small increase in AEP has a significant impact on reducing the cost of energy. The costs of producing blades with different tips is relatively small compared to the improved power output, so the InnoTip project could lead to a cost of energy-reduction of up to 2 percent, making the use of wind energy more competitive.
The project partners came up with three different optimised geometries for testing: a shark fin tip, a winglet tip and turbulators. Each tip design has different ways of increasing the turbine yield. For instance, the bending of the blade tip (winglet) effectively increases the length of the blade but in an altered direction. This will have some beneficial effects on the complex aerodynamic phenomena in the tip area of the blade. The turbulator causes a faster mixture of the wake, which is beneficial for the turbines further downstream in the wind farm.
Putting the tips to the test
Once the three new tips were designed, it was time to put them to the test at TNO’s test site in the Dutch Wieringermeer. But manufacturing full test blades with each of the different tip designs would be expensive, so the InnoTip team came up with a more practical solution. Instead of building new blades, the team would replace only the tips on blades already in operation – almost like putting a “sock” on the end of a blade. This was a unique and complex challenge. After the experiments, all the tips were successfully removed without damaging the blades so that the turbines could continue to operate safely. For the Innotip project, four test turbines at TNO's test site were heavily equipped with measurement sensors to obtain highly accurate data to assess the actual potential of the tips correctly. The experiments were done with the side-by-side configuration where all the tips were on the turbines and measured at the same time for the same wind climate.
Managing environmental and safety risks
As it was quite unique to perform such a complex and innovative experiment on a wind farm in operation, Innotip not only delivered technical knowledge and insights but due to safety concerns of inhabitants nearby the test site, the project team also assessed the environmental and safety risks to ensure a safe experiment, which has further deepened our knowledge on managing environmental risks and public perception around working wind farms. We combine knowledge on both technology and operations as well as on permits and safety.