Computational prediction of surface roughness due to leading edge erosion of wind turbine blades

The observed erosion of the leading edge of wind turbine blades by impacts of rain droplets and other environmental particles is a major concern for the wind industry. The eroded leading edge profiles can reduce the aerodynamic efficiency of blades and lead to energy production losses. Severe erosion also requires costly repairs. Recent research has been focused on estimating the lifetime of protective coating materials with computational tools, taking into account the complex mechanical properties of coatings. This thesis aims to extend existing modeling tools to not only provide estimates of coating lifetimes but also to predict the state of surface damage in terms of roughness evolution and depth of erosion. This can be useful for predicting the effect on blade aerodynamics. Simulations of rain droplet impacts are also used to study how surface damage affects impact dynamics and stresses in the coating.

The first of the two developed approaches could provide predictions for the duration of the erosion incubation period and time to reach coating breakthrough, with errors in the order of 50 % when compared with rain erosion test data. Furthermore, lower peak principal tensile strains and stresses from the droplet impact simulations correlated with better erosion performance. The second approach focuses on uniform leading edge erosion damage patterns and was able to reproduce surface damage patterns observed in scans of rain erosion test samples, while it can also simulate the evolution of damage profiles. The results of the simulations of droplet impacts on damaged coating surfaces suggest that the largest stress values occur at the base of erosion craters due to the formation of high-speed jets.

Finally, an extension of one of the developed approaches to provide estimations for the depth and width of erosion along the length of blades is presented and different distributions of coating defects along the blade are considered. The different types and distributions of defects led to very different lifetimes and surface damage patterns, which can have a different effect on blade aerodynamics.