CFD analysis of droplet impact pressure for prediction of rain erosion of wind turbine blades

Rain erosion is a prominent issue in Offshore Wind Turbines (OWT) with wind farms experiencing heavy and frequent rainfall compared to onshore conditions. A simplified Springer model is used widely by industries to predict erosion initiation in composite materials and has been under various recent investigations to improve its predictability of rain erosion. However, the Springer model uses the modified water hammer equation to compute impact pressure, and it does not consider the impact of droplet sizes. This Computational Fluid Dynamic (CFD) study is motivated to develop an understanding of the effect of droplet sizes on impact pressure while discussing impact behaviour in detail. Simulations were conducted for droplet diameters ranging between 1 to 5 mm with an impact speed of 100 m/s. The results show that the water droplets slightly deform just before the impact, delaying the impact time due to the pressurised air layer in between the droplet and substrate. During this delay period, the impact pressure was significantly increased to reach the maximum impact pressure. Maximum impact pressure was found to increase with the droplet size, due to high air volume displacement whereas, this phenomenon is not accounted for in pressure estimation in the Springer model. In conclusion, the larger droplets were observed to impose higher pressure on the blade’s coating than the smaller droplets, which can lead to high erosion levels.