Erosion resistant blade coatings for wind turbines

Wind energy is attracting global interest. The installed worldwide wind turbine capacity has increased dramatically in the past decade, and wind energy presently covers 1.8 per cent of the world’s electricity (i.e in 2015 equivalent of 42.1 per cent of Denmark's total electricity consumption). To make the electricity production more efficient, the wind turbines and their rotor diameter are getting bigger. Presently, the largest rotor diameter exceeds 170 m with 8 MW capacity. Rotor diameters of 250 m with 20 MW capacity are anticipated. Large diameter rotors means high wing tip speeds; presently the max tip speed is 100 m/s.

Composite wind turbine blades are designed to last for about 20-25 years in the field. However, the composite materials are susceptible to heat, moisture, UV radiation, and especially erosion from both solid particles and rain. Erosion can occur as soon as two years after installation. The erosion process on wind turbine blades typically starts with the formation of small pits or from small tears or scratches in the leading edge which may act as initiation sites for further erosion. The defects will increase in size and density over time and combine to cause delamination of the leading edge. If repairs are not done early, damage to the underlying laminate will be present as early as after five years.

The break down mechanisms are not fully understood; however, apart from the protecting material's ability to withstand a single impact, also the relation between the rain drop impact period and the relaxation time is important. The underlying mechanisms behind drop impact erosion involve interactions of several stress (pressure) waves in combination with successive drop impacts.

The industrial standard to investigate simulated impact from raindrops is the so-called whirling arm erosion test rig or rain erosion test (RET). In CoaST, we aim at developing a novel setup which simulates the raindrops' impact.

The disciplines involved in understanding the working mechanisms of leading edge protection systems (blade coatings) and the break down mechanisms are mainly polymer chemistry, fluid mechanics and fracture mechanics.