Hydrodynamic and material response to droplet impact on coated turbine blades: implications for cavitation erosion

The impact of droplets, such as rain and sea sprays, on wind turbine blade surfaces can lead to significant damage due to leading-edge erosion (LEE). Traditionally, LEE on wind turbine blades has been solely attributed to material fatigue from repeated impacts; however, studies in similar engineering applications, such as steam turbines, suggest that cavitation may also play a critical role. This study develops a novel fluid–structure interaction (FSI) model that, for the first time, explicitly incorporates phase change in the liquid flow inside the droplet. Droplet impingement simulations cover a broad range of impact speeds relevant to most engineering applications, considering both cavitation and non-cavitation scenarios. The results present temporal evolutions of the pressure wave inside the droplet during its impact on the solid surface and demonstrates the triggering mechanisms of both homogeneous and heterogeneous cavitation. The developed FSI model suggests that the significant impact of cavitation, which can subject the material to two separate stress events during a single droplet impact, potentially reduces the material’s fatigue lifetime by half. Furthermore, the study explores the ability of heterogeneous cavitation to cause localised damage on the coating surface upon a single raindrop impact at speeds below 100 100 100 normal m normal s Superscript negative 1 m s − 1 m\, s^-1. The comparison of two-dimensional and axisymmetric simulations shows that the intensified shock waves in the latter produce more focused cavitation near the surface centre, with minimal spreading along the surface. These findings highlight the need to incorporate heterogeneous cavitation effects in future studies, particularly as the turbine blade size and impact velocities increase.