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%.
The blade design of a horizontal axis wind turbine (HAWT) prioritizes structural stability over aerodynamic performance, which results in power loss caused by stalling in the inboard regions. In this study, a vortex generator (VG) was employed for stall control. Because the generated vortex intensity varies with the VG geometry and size, design values based on the aerodynamic characteristics of airfoils in a wind turbine blade were considered. The VG design values for the HAWT were determined based on the computational fluid dynamics (CFD) analysis of the airfoil in the blade region with the maximum chord length. VG applicability was examined for all airfoils applied to the blade inboard region. Based on the lift and drag data obtained through the CFD analysis, the performance improvement of the wind turbine was analyzed through the blade element momentum theory. This analysis also incorporated the angle of attack of the airfoil, which differed for each local cross section in a wind turbine. The VG application increased the wind turbine power for each wind speed interval by an average of 2.5% and the annual energy production by up to 2.7%. The application of the proposed VG design to the inboard region can control the radial flow generated near the hub, improving the aerodynamic performance and decreasing the power loss.
Savonius vertical axis wind turbines have simple structures, can self-start in environments with low wind speed and strong turbulence intensity, and can be installed at low costs. Therefore, installation is possible in urban centers with low wind speeds, which may contribute to the construction of a decentralized power system. Savonius wind turbines are operated by drag force, with the blades moving in the same direction as the flow current providing the thrust force and those moving in the opposite direction of the wind being rotated by the drag force. In this study, the Savonius wind turbine design was examined to develop a stable wind turbine for use in urban centers at low wind speeds. The Savonius rotor design variables (aspect and overlap ratios) and blade forms (semi-circular, Bach, and elliptical type) were examined using computational fluid dynamics analysis. Moreover, a rotor capable of providing the target output was designed and maximum rotor efficiency of 18% was realized. Further, changes to the flow corresponding with various turbine layouts were analyzed to determine the arrangement that would maximize turbine performance. The results showed that the maximum efficiency of the turbines was in the 17–19% range and without significant variation.
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