Energy Technology Centre Ltd (ETC) provides water droplet erosion testing for wind turbine blades. Damage from water droplet erosion can reduce performance and lead to 3-5% power losses and repairs and replacements are costly, particularly in offshore environments. Reducing erosion has a big economic benefit. ETC worked with NPL to explore techniques for measuring material erosion during the testing process.
Testing compares materials under the same erosion conditions, showing which are most durable. The blades are placed in a test rig where they spin on an arm to simulate normal operating speeds and are struck with water droplets, simulating the erosion mechanisms experienced in operation on an accelerated time scale. This allows them to compare materials and coatings to identify the most durable designs. However, there are many unknowns around how testing conditions relate to real life.
Assessing the materials under test currently involves stopping at discrete intervals for visual inspections and making mass loss measurements. This only shows what the damage is, but not how and when it occurred. It is also a laborious and time-consuming process and some evidence suggests that stopping and starting compromises results.
ETC wanted to improve their testing by developing a system that could monitor erosion throughout testing and make assessments based on more reliable indicators. This was no small challenge, since it required detecting micrometre level changes in blades moving at up to 150m/s.
ETC were not aware of any such technique, so they applied to the Analysis for Innovators (A4I) Programme to investigate a possible solution.