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Fraunhofer IWES scientists have proposed alternative methods like thermography and acoustic monitoring for inspecting wind turbine rotor blades.

According to the researchers, offshore drones equipped with thermal imaging cameras in combination with acoustic monitoring systems could potentially improve maintenance efficiency and help reduce downtime of wind turbines.

Wind turbines have a design life of 20 years. The rotor blades must be regularly inspected at least once every four years to verify their structural integrity. 

Continuous structural health monitoring (SHM) of rotor blades contributes significantly to the overall cost-efficiency of wind energy turbines. When the rotor is turning, the blade tips can reach a speed of 300 to 350 km/h – as fast as a Formula-1 racing car.

Rotor blades deliver their best aerodynamic performance when the boundary layer of wind flows smoothly over the airfoil without causing wake effects. Even the slightest surface damage can generate turbulence, resulting in lower efficiency. For a wind turbine, this means diminished output, less cost-effective operation, and a shorter service life.

Moreover, the extreme conditions out at sea cause materials to degrade much faster than on land. Specific stress factors include greater exposure to UV radiation, high wind speeds and salt-laden air. 

These issues are being addressed by the Thermoflight Research Project featuring researchers from Fraunhofer IWES together with WindMW Service GmbH, the Bremen Institute for Metrology, Automation and Quality Science (BIMAQ), and Deutsche WindGuard Engineering GmbH.

The goal to reduce wind turbine downtime and perform maintenance with fewer personnel has resulted in two approaches: One approach involves the use of drones in combination with mobile thermography technology; the other employs an acoustic emission monitoring system.

The acoustic emission measuring system integrated in the rotor blade serves as an early warning system by detecting internal damage. As soon as the sensors detect and localize a potential defect, appropriate measures can be initiated.

Depending on the type of damage and its location, a closer, external inspection of the rotor blade could, for example, be carried out using a thermal imaging camera.

Image credits and content: Seilpartner GmbH/Fraunhofer IWES

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