Characterization of a pulsating water jet for rain erosion testing of blade coatings: Flow visualization, pressure investigation, and damage analysis

In the past decade or so, blade coatings have become state-of-the-art technology for the protection of wind turbine blades against particle and rain erosion. The present work considers the application of a high-frequency pulsating water jet, based on a passive acoustic-type nozzle, for accelerated rain erosion evaluation of blade coatings. Using high-speed image visualization and impact pressure investigation, the flow properties were systematically characterized, providing both qualitative and quantitative understanding of the key flow parameters. Continuous, pulsating and expanding flow zones, at velocities from 99 to 143 m/s, were classified for standoff distances within 120 mm. For a reference blade coating, the pulsating jet produced more realistic erosion patterns than the continuous flow. Furthermore, high-frequency impacts at around 7500 impacts/s led to fast fatigue accumulation, and enhanced lateral jetting effects, all of which shortened the coating erosion lifetime. In summary, for this work, a high-frequency pulsating water jet, for accelerated erosion studies on wind turbine blade coatings, was constructed and applied.