Wind turbine blades let flexible coatings take the strain to beat erosion
As the size of a wind turbine increases, so does the speed at the tip of the blades and consequently the erosion of their forward-facing leading edges due to the effects of rain, dust and suspended particles. This erosion is increasing not only in terms of damage but also in the rate of its occurrence; this is particularly true for offshore wind turbines with large blades, high tip speeds and high wind speeds. Due to the negative economic effect of blade erosion, all wind turbine manufacturers are actively seeking a solution, such as adapting protective coatings from the aerospace and defence industries. However, these coatings have failed much earlier in service than predicted as they do not address all the factors affecting blade erosion. Examples include the interaction between the different layers conforming the blade's protective coating system and the influence of the application processes on the coating’s performance. The EU-funded LEP4BLADES project addressed this challenge. The partners did so by developing an innovative leading-edge protection (LEP) polymeric coating with special mechanical and chemical properties that avoid the erosion problem during the whole lifetime of the wind turbine blade.
A new approach
A novel LEP coating solution developed by Spanish SME Aerox Advanced Polymers consists of a new family of polymers using hybrid polyurea-polyurethane technology with an outstanding mechanical and chemical resistance. The technology is based on the precise combination of two thermoset polymers with different rheological, thermal, chemical and physical properties. This creates a high-performance material with extraordinary erosion resistance, explains project coordinator Guillermo Mas. “Aerox proprietary technology allows us to design and modify the properties of the polymer, considering the harsh environment conditions where wind blades operate as well as the particularities of each wind blade manufacturing technology and materials.”
Improved properties
Moreover, analytic hierarchy process (AHP) technology allows for adjustment of the coating’s compatibility with the material of the blade. This mechanical compatibility is essential for dissipation of the effects caused by the impacts throughout the whole structure of the blade. “Thanks to AHP technology, the material is provided with viscoelastic behaviour and adjustable compatibility, making it able to absorb high-speed and high-frequency impacts caused by raindrops and other particles hitting the leading edge of the blades,” explains Mas. The viscous properties allow the coating to deform and absorb the stress caused by the impact of the droplet, and the elastic properties ensure the complete recover of the coating surface under repeated impacts with high strain-rate conditions. At the same time, the stress waves created by the impact are transmitted from the coating to the blade, minimising their reflexion and avoiding the existence of stress concentration points where the erosion is usually initiated. LEP4BLADES therefore provided a LEP system for wind turbine blades with outstanding applicability and improved rain erosion resistance, compared to currently existing solutions. “It also allowed us to have deeper knowledge of rain erosion mechanisms and the theoretical models describing their effect as well as a better understanding of the results of rain erosion tests and its correlation with real working conditions of wind turbine blades,” Mas concludes.
Keywords
LEP4BLADES, blade, coating, erosion, wind turbine, leading edge, polyurea, polyurethane, analytic hierarchy process
