Investigation of droplet path in a rain erosion tester

Erosion of the leading edges of wind turbine blades due to the repeated impact of rain droplets at high speed over time can wear down the blade surfaces to the extent that power production is significantly reduced for the wind turbines. Therefore a rain erosion tester, which is a test bench for accelerated test of leading erosion due to rain impact, can be used to assess the durability of different leading edge materials and coatings. Since the droplet relative speed and size at impact is of key importance to the erosion process, it is important to know how these are affected by the complex flow disturbances stemming from the rain erosion tester itself. This is investigated in the present work using high speed camera recordings and CFD. The high speed camera recordings reveal that the droplets do not break up before impact at the surface, and that the path of the droplets is relatively undisturbed by the flow induced by the rain erosion tester. The comparison with droplet paths simulated in CFD is in good agreement with this result. The CFD simulations further indicate that an inaccurately set pitch angle of the blades can result in a very different flowfield in the RET, which can significantly alter the droplet trajectories.