Investigating Damage Initiation in Wind Turbine Blade Coating Under Repeated Raindrop Impacts

The Wind Turbine Blade (WTB) coating is a protective layer that sustains repeated raindrop impacts. These impacts cause cyclic stresses, fatigue, and the resulting erosion of the leading edge of the blade coating. The high-intensity rains in India make this problem more critical. The presence of voids (manufacturing defects) in the coating leads to local stress concentration and enhances the intensity of erosion. This erosion causes an increase in the drag coefficient and a reduction in the lift coefficient leading to an underperformance of the turbine. Several studies are reported in the literature to understand the damage estimation of the coating. However, the effects of the voids radii and their locations on the rate of degradation of the coating due to repeated impacts need further investigation. In the present study, it is learnt that voids in the coating cause faster damage propagation. That results in the deterioration of the impact-damping performance, causing an early failure of the material. The study also demonstrates that in the case of coating without voids, the damage starts from the surface and travels downwards. Whereas, in the case of coating with voids, the damage accumulates rapidly in its vicinity. The study is performed in two steps. Firstly, the stresses in the coating are computed using a finite element model employing smoothed particle hydrodynamics (SPH) in ABAQUS/Explicit. Hence, the fluid-solid interaction study is performed. In the second stage, the fatigue damage of coating is predicted by employing the continuum damage mechanics (CDM) approach. The comparison of results in the above two cases demonstrates that the present model with voids is found to be more realistic for estimating nonlinear damage accumulation, micro-cracks initiation and growth. Thus, it is presently adopted to visualise the effect of voids radii and their locations on WT coating subjected to rain-induced fatigue. The results obtained by the present realistic model are validated with the established experimental observations.