International. Fraunhofer's team manages to protect turbine blades against ice with drones.
The new technique has been jointly developed by experts from the Fraunhofer Institute for Manufacturing Technology and Advanced Materials IFAM and the Fraunhofer Institute for Manufacturing Engineering and Automation IPA in the project 'TURBO - Temporary coating using drones'.
"Drones that are only used when necessary offer a cost-effective alternative," says Andreas Stake, project manager at Fraunhofer IFAM. However, in order to be able to use drones to prevent ice, a number of conditions must be met.
In addition to being environmentally friendly, coating materials must demonstrate good adhesion and durability sufficient to stay on the rotors for weeks and protect them from ice. The spraying system used must be very precise and at the same time lightweight. And finally, drones must have a high payload and allow for very precise control.
The Fraunhofer researchers working on the Turbo project managed to develop a prototype that meets all these requirements. The coating material designed by the scientists at Fraunhofer IFAM Bremen consists of urea and wax, is environmentally friendly and has good adhesion.
The material can be applied quickly and easily using the spray technique and also dries quickly. The coating was tested in an ice chamber at the institute to confirm that it reliably protects against frost formation.
The Fraunhofer IPA team built the equipment used to apply the coating. It consists of a small pump that presses the fluid mixture of urea and wax under high pressure inside a long, thin lance, at the tip of which is a nozzle with a diameter of only 0.3 millimeters.
The airless pump system is capable of producing droplets with a diameter of 100 micrometers. Even in winds of 35 kilometers per hour, these droplets can still be sprayed accurately onto the edges of the rotor blades, where they then solidify. The edges are particularly important as this is where the icing process begins when cold, moist air hits the turbine.
Dr. Oliver Tiedje, Project Manager at Fraunhofer IPA, and his team determined the technical parameters; for example, the required pressure, an efficient atomization method, and the optimal droplet size using fluid dynamics simulations.
"Our decades of experience modeling coating processes helped us a lot. We were able to take advantage of this experience," said Dr. Tiedje.
"However, we had to adapt the process parameters to the complex geometry of the wind turbines," he said.
The researchers now intend to work with industry partners to further develop the technique and prepare it for mass production.
There are numerous applications where drones can be used to apply coatings, ranging from ice protection for wind turbines and overhead lines in rail transport to building renovation; for example, the repair of plaster defects in parts of buildings that are difficult to access.
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