Numerical Investigation of the Effect of Pre-Existing Surface Craters on Failure of Leading Edge Protection Coatings for Wind Turbine Blades

This study investigates how pre-existing surface craters of leading edge protection coating used against rain erosion of wind turbine blades affect the maximum strains during impacts of rain droplets. Surface craters in the form of pinholes can form during the coating application process. The investigation is carried out by using finite element models of droplet impacts on surfaces with craters, where the impact velocity, droplet size, and crater position and size are varied. The simulations predict that the maximum strain is located at the crater walls and increases as the impact velocity and droplet size increase, and that craters closer to the central impact axis experience larger strains than craters placed farther away. The size of the crater was not predicted to have an influence on strains. The position of the maximum strain value was at the crater walls for all cases, and it was larger than for an impact on a flat surface. Observations from rain erosion tests suggest that some fractures initiate from pre-existing craters which act as weak points of otherwise highly resistant coatings.