Nickel cobalt tiles integrated into a blade could do much more than just protect them – it could make new blades and lighter nacelles possible
An innovative solution to blade leading edge erosion that applies technology proven in the aerospace industry is ready to be tested in a demonstrator programme.
Scientists at the Offshore Renewable Energy Catapult (ORE Catapult) in the UK believe that, apart from protecting existing turbines, it could facilitate the use of offshore wind turbines with higher tip speeds, paving the way for lighter, less expensive wind turbine blades and drivetrains.
ORE Catapult research structural engineer Dr Peter Greaves told an April webinar organised by Fraunhofer IWES in Germany that the Leading Edge for Turbines (LEFT) project, which is part-funded by Innovate UK, had developed a tool that could generate a mesh between the blade of a turbine and a protective tile system that uses nickel cobalt (Ni-Co) tiles.
The aim of the project was to investigate and validate a way to attach tiles to blades, in addition to considering how to integrate the design of the Ni-Co leading edge into the overall design and functionality of turbine blades. The nickel cobalt alloy has the best rain erosion performance of all of the products tested in ORE Catapult’s rain erosion test rig.
Dr Greaves explained that a model chain had been developed that can accurately predict the adhesive stresses in the Ni-Co tile system and be used with more detailed models developed from CAD. He said the next steps in the project would be to produce a demonstrator of the leading edge system, investigate how the interface between tiles affects the stress, look into certification for the new concept and investigate its effect on a blade lightning protection system.
Over the last two years, the project partners – Radius Aerospace UK, Performance Engineered Solutions Ltd and the ORE Catapult – worked to transfer the use of electroformed Ni-Co leading edge protection systems from the aerospace industry to wind turbines.
Dr Greaves said the Ni-Co solution had demonstrated extremely good rain erosion performance and lasted for 85 hours in the ORE Catapult rain erosion rig at 173 m/s. “Typical solutions last for around 15 hours at 120 m/s.”
But as he also explained, it is challenging to integrate the electroformed Ni-Co tiles with wind turbine blades because the alloy has high relative stiffness compared to the blade. If this challenge can be overcome, he explained, the benefits could be significant.
“If the speed limit of leading edge erosion is removed, then tip speeds could increase to 120 m/s or more, which is a 30% increase on current speeds. That would mean not only would the tiles enhance edge erosion, they could one day lead to the introduction of larger, lighter blades and smaller nacelles and subsystems.
“A nacelle mass trend derived from a survey of current nacelles showed the estimated nacelle mass for a 20-MW turbine would be 1,025 tonnes at a tip speed of 90 m/s but only 815 tonnes at 120 m/s,” Dr Greaves explained. “This would lead to a substantial reduction in tower cost as well as nacelle cost.”
Dr Greaves said earlier work demonstrated that a turbine capex reduction of 20% could be achieved for a 5-MW turbine when increasing the tip speed and moving to a downwind rotor. It has also been demonstrated that a 5.5% reduction in levelised cost of energy could be achieved by moving from 80 m/s to a 100 m/s flexible blade. During the project, a high tip speed rotor design was studied that would have reduced nacelle mass. Moving from 90 m/s to 110 m/s led to an estimated nacelle mass reduction of 150 tonnes.
Leading edge erosion is caused by raindrops or ‘hydrometeors’ impacting the leading edge near to the tip of the blade, where the local velocity can be close to 100 m/s. It is a significant problem for the offshore wind industry and costs the industry in two ways: aerodynamic performance decreases as erosion gets worse, and repairs need to be carried out on a regular basis.
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