Prediction of the Aerodynamic Performance Degradation due to Insect Contamination

When insects collide with the wind turbine blades, their exoskeletons break, releasing bodily fluids. These fluids increase in viscosity when exposed to oxygen, causing the insect remains to adhere to the blade surface, a phenomenon known as insect contamination. This contamination increases surface roughness, reducing lift and increasing drag, thus leading to a degradation in aerodynamic performance. According to the study by Madsen, A. [1], this phenomenon can lead to a 25% reduction in power generation.
Blades should be cleaned regularly to avoid insect contamination. However, the costs associated with cleaning and turbine downtime pose significant economic burdens. Therefore, it would be beneficial to have monitoring tools to support decision-making on whether to continue operating turbines with reduced efficiency due to insect contamination or to temporarily suspend power generation for blade cleaning. However, not many studies have been performed yet.
Early research primarily employed experimental approaches to predict the locations where insects adhere to the airfoil. With advancements in computational technology, Wilcox and White [1] applied simulation techniques to forecast insect trajectories and adhesion patterns on surfaces using LEWICE [2]. Their simulations revealed that insect adhesion is most significant at the stagnation point and decreases toward the trailing edge. Furthermore, they found that larger and faster-moving insects adhere more strongly and are less influenced by airflow, maintaining more linear trajectories. However, had limitations in accurately predicting lift-to-drag performance, as they failed to account for surface roughness increases caused by insect adhesion and the resulting changes in flow characteristics because of using the panel methods and boundary layer theory provided by LEWICE.
To address this gap, the present study employs state-of-the-art simulation techniques using the CFD technique to predict the distribution of insects adhering to wind turbine blades and explain surface roughness changes over time. Specifically, this research refines the prediction of insect trajectories and impact velocities by incorporating the rupture velocity of insects, and factors such as average insect size and altitude-dependent insect density. The model ensures that adhesion only occurs when the impact velocity exceeds the rupture velocity. Furthermore, in order to analyse the effect of localised surface roughness due to insect contamination on aerodynamic performance, a turbulence model [3] capable of describing flow transition induced by roughness is applied, enabling a more accurate assessment of lift reduction and drag increase over time.