Leading Edge Rain Erosion and Lifetime Prediction of Advanced Polymer Coatings for Wind Turbine Blades

Abstract

The increasing focus on sustainable living and the need to reduce dependency on fossil fuels has led to a growing interest in renewable energy sources. Among these, the wind energy sector has not only experienced significant growth in terms of numbers but also in size. Larger turbines lead to more severe leading-edge erosion and further increase operation and maintenance costs. To mitigate this problem, the new advanced leading-edge protection has become vital in the wind energy sector. This thesis focuses on the evaluation of two polymer coating materials (PA and PD) using a Pulsating Jet Erosion Test (PJET) setup.

The first aim of this thesis is to propose a novel analysis method to address the issue of volume interdependence in the PJET. To achieve this, a concept called "equivalent velocity" is introduced. The equivalent velocity represents the velocity at which a spherical droplet should impact a surface to exert the same kinetic energy per impingement as the actual water slug moving at the impact velocity. By utilizing this concept, the velocity-number of impacts plot takes into account the volume interdependence in erosion experiments.

The second aim is to utilize the PJET to analyze the erosion behavior of PA and PD coatings. The investigation focuses on understanding the relationship between impact velocity and the number of impacts until the incubation period and the breakthrough. The incubation period refers to the interval until the damage is visible and the breakthrough is the moment until the filler underneath the coating is exposed. Additionally, the erosion damage progression of the coatings was analyzed, and the lifetime prediction was evaluated using an existing long-term leading-edge rain erosion model.

The experimental results revealed that the ductile material (PD) exhibits a longer resistance to erosion compared to the stiff material (PA), with the mean number of impacts until breakthrough being 2 to 3 times higher for PD. Moreover, the long-term leading-edge rain erosion model highlights the importance of the accurate measurement of material properties, as lifetime prediction is very sensitive to ultimate tensile strength and Poisson’s ratio.

However, it is crucial to validate the equivalent velocity method through experiments and numerical modeling, while also improving the experimental method to allow for continuous observation of the erosion process in a controlled environment with temperature and humidity regulation. Conducting tests in a wider range of velocities is also recommended. Additionally, improvements for the rain erosion model are necessary to accommodate the utilization of the equivalent velocity.