Fraunhofer to test blade coatings

Researchers at Germany’s Fraunhofer IWES are developing a new test bench that will be able to gauge how a rotor blade’s coating will stand up to long-term environmental erosion.

The “climatised” rig, which will have rotating arms able to trial blades at tip speeds of up to 160 metres per second, will be used to evaluate the impact rain, hail, sand, seawater and dirt have on the surface of blades, particularly the leading edge.

Environmental conditions combined with temperature changes and UV radiation can lead to a blade’s aerodynamics being undermined by material abrasion and crack formation, lowering efficiency and increasing operation noise.

“The test conditions [on the rig] are variable – rotational speeds and climatic conditions can be adjusted individually according to the respective real rotor blade operating conditions,” explains Fraunhofer’s Benjamin Buchholz, who is heading up the government-funded €1.4m ($1.9bn)“Rotor Blade Rain Erosion” project.

“Weather and operational data records provide the necessary bases. In this way we hope to equally ensure test stand quality and the validity of the results obtained.”

Assessing damage mechanisms will inform thinking on optimisation of coating materials such as foils and paint and for the introduction of further measures “such as changes in [wind turbine] operational management or adjustments to maintenance intervals.”

These issues, Buchholz notes, will becoming more pressing as larger, more efficient rotors are developed that spin at faster RPMs and so are “struck harder” by precipitation.

Project partners include the Fraunhofer Institute for Production Technology and Applied Material Research, industrial coatings manufacturers BASF Coating and Epurex Films, rotor blade and wind energy consultants CP Max Rotortechnik and GETproject, and the Renewable Energy Test Centre.

Alongside the Fraunhofer project, partner company Automation Dr Nix is working on a mobile system for “contactless” domain-terahertz-spectroscopy testing for rotor blade quality control and coating thickness measurements.