Numerical study on the effect of blade surface deterioration by erosion on the performance of a large wind turbine

Abstract

As the demand for the development of onshore wind farms in areas with low wind speeds and large offshore wind farms increases, the size of the wind turbine and its rotor has also increased rapidly. An increase in the rotor diameter implies an increase in the relative wind velocity (with respect to each cross section in the radial direction of the blade) near the tip region of the blade. This in return accelerates the surface damage caused by the erosion of the leading edge, thereby increasing the frequency of maintenance and lowering competitiveness in the cost of energy. In this study, computational fluid dynamics (CFD) analysis was performed to analyze the correlation between the leading-edge erosion damage and output performance of the blade. CFD simulations were performed using a tip airfoil (NACA 64_618) and a full-scale wind turbine (NREL 5 MW) based on the state of erosion of discarded blades considering approximately 12 years of maintenance-free operation. The irregular erosion at the airfoil leading edge results in premature stall phenomena and reduces the aerodynamic efficiency. Thus, the accurate analysis of the flow separation point and flow change is necessary. Therefore, three-dimensional transient CFD analysis was performed to consider the complex flow generated on the blade surface. The erosion at the leading edge reduced the airfoil lift by up to 23% and drag by 100%, reducing the aerodynamic efficiency, which in effect reduced annual energy production by up to 4%.