Rain erosion is a critical issue for the development of wind power generation because it limits the lifetime of wind turbine blades. To clarify the erosion initiation mechanism in wind turbine blades of metallic material, pit formation and erosion initiation on a smooth wet wall of aluminum materials A3003 and annealed A5052 were investigated; water droplets were impinged on the wall using a pulsed-jet tester; and combined theoretical and numerical studies were performed by considering the influence of the water film on the wall. Although the theoretical and numerical impact pressures were much lower than the offset yield strength of the materials, random pit formation and erosion initiation were observed on the target material. To clarify the reason for this, the occurrence of cavitation erosion was investigated based on the numerical pressure distribution of a droplet impacting a wet wall. The numerical results showed that the pressures in the droplet center and water film became lower than the saturated vapor pressure, suggesting the occurrence of cavitation erosion. Furthermore, a similar pit formation and erosion initiation were observed on the wall material in the acoustic cavitation test under the cavitation erosion condition. These results indicate that the pit formation could have been caused by the high impact pressure caused by the micro-jet mechanism that occurs when a droplet impacts the wet wall. This could potentially explain the mechanism of the more severe erosion in the actual wind turbine blade than was expected.
Nobuyuki FUJISAWA (Fri,) studied this question.