Growth through Research, development & demonstration in Offshore Wind

Turbine control strategies to mitigate leading-edge erosion reduces O&M costs significantly

In this way, the lifetime of wind turbine blades is significantly extended.

The WINDCORE project develops optimized rotor control strategies, based on reducing the rotor speed during heavy precipitations. In this way, the lifetime of wind turbine blades is significantly extended. The project determines the optimal speed to operate the rotor within several given rain intensities. Through aerodynamical computer simulations, modelling and laboratory testing of the leading edge erosion process and characterization of the critical precipitation condition the optimal speed during harsh conditions is related to specific offshore environmental conditions. An interview with Harald van der Mijle Meijer and Sandro Di Noi about their findings.

They did not know each other before the start of the project. The three major initiators of the WINDCORE project found each other on a common problem. Sandro Di Noi of turbine manufacturer Suzlon has been working for some time with Julie Teuwen of TU Delft to understand more about how blade erosion occurs. In parallel, Harald van der Mijle Meijen of TNO and a few colleagues devised a plan to determine the influence of turbine control strategies on the occurrence of erosion. That was a strategy Suzlon hadn't thought of before. When the protagonists met, things moved quickly. Within a year, the WINDCORE project was set up and the project could start. Shell and RWE also joined the project team and were able to contribute mainly through their operational experience with offshore wind turbines. In addition, there was a close collaboration with 3M, a supplier of coatings and tapes for turbine blades.

Sandro has been working in the wind industry for more than 11 years, of which 5 years in Hengelo in the R&D department of Suzlon. Suzlon is a turbine manufacturer from India and is preparing for the local offshore market they see coming. Sandro says the project has exceeded expectations in many aspects: “We have made great progress in predicting leading-edge erosion. That is important to us.” Harald added that they learned a lot about the impact of surface damage on turbine performance and how maintenance strategy can affect costs: "blade maintenance is an important part of the total O&M costs. In the project, TNO has been able to significantly improve the cost models by bringing together new operational data in the field of turbine maintenance and by improving insights into the origin of blade erosion."

Not everything went smoothly

But all this was not without a struggle. First of all, the test facilities at TU Delft had to be adapted urgently because the existing lab set-up turned out to be not accurate enough. Tests were used to investigate the effects of precipitation on the blades under different weather conditions (rain, hail) and turbine conditions (speed and type of blade, type of coating). The quick adjustment allowed the test results to be obtained on time, and sufficient time was left to interpret the results and adapt the erosion models accordingly. Sandro says he was very satisfied with the consortium because the problem owner and the researchers are in one project and worked closely together to find solutions.

It soon became apparent that not all weather data was available. In some cases, the correct sensors were present at measuring points, but they were simply not switched on. In the end, KNMI shared data about onshore locations . Harald: “It was a challenge to properly extrapolate this data to offshore conditions”.

Additional weather data is needed

It soon became clear to the project team that to take bigger steps, better data had to be made available. Harald: “Gradually, we began to understand the importance of good and consistent weather data. We can only really improve the models when this kind of data becomes available. We have therefore joined forces with several parties and set up the PROWESS project to generate reliable data sets. PROWESS stands for Precipitation atlas for Offshore Wind blade Erosion Support System, and should produce a precipitation atlas for the Dutch part of the North Sea.” The project has already been approved by RVO and has started.

Important results

Sandro: “An important result of the WINDCORE project for us is the model to predict the end of incubation time.” The type of coating, speed of the blades, type of precipitation and other weather conditions are all factors that influence this. Sandro: "We now understand that the tip speed and the type of drop have the greatest influence on erosion formation."

Nevertheless, the project made it clear that it remains difficult to match the results of the laboratory tests with real events. The current model is well able to determine the erosion for one type. The next step is to get the lab testing for other types of coatings equivalent to many years of use. Sandro explains that Suzlon is already using the model: "The model gives us feedback on specific coating use. However, a good interpretation requires many detailed coating parameters, which are still difficult to obtain."

Collaboration

Sandro and Harald don't think twice about what they were most pleased about. Harald: “I'm proud of the cooperation and the flexible ‘out-of-the-box thinking’. The barriers that we have solved together and the proactive way of working. It was fun to work together. I am looking forward to collaborate again in the next project.” Sandro adds that the results were above expectations and also expresses his satisfaction with the teamwork: “We are certainly not tired of working together”.

Next step – follow-up project

Definitely, the team wants to take the challenge of leading-edge corrosion one step further. A follow-up project is currently being prepared, with the same core team. The project will make use of TNO's modelling competence and TUD's competence of erosion and their material knowledge to predict (or confirm) the progress in erosion.

In the first project, the coating manufacturer 3M could be consulted, but they were not involved as a project partner. The great desire for this new project is for a major manufacturer of leading-edge protection systems to become a project partner. Harald: “Comparing products can worry manufacturers. But they can benefit from it, better understand the mechanism of erosion. It is a complex matter to fully understand the entire mechanism.” In addition, also a partner who does the maintenance of blades, e.g. using drone inspection may join. It will affect their business model. We are in talks with possible other new partners.

Advice to other consortia

Harald also gives some advice. He says it's important to share your results: “Dissemination of knowledge, for example through conferences, is very important because it connects you with other experts, also with different areas of expertise. This way you get your results implemented as well as possible and you also get fresh new ideas. We plan to do it the same way in future projects.”

Harald gives a concrete example: “A very different approach to measuring droplet size and number was presented at a meteorological conference. As a result, we came into contact with specialists in certain sensors, who could measure the required properties. This is also where we started the precipitation atlas initiative, which we now know as PROWESS.”

A damaged blade
A damaged blade
magnify
Harald van der Mijle Meijer and Sandro Di Noi
Harald van der Mijle Meijer and Sandro Di Noi
magnify