Blade design trade-offs using low-lift airfoils for stall-regulated HAWTs

A systematic blade design study was conducted to explore the trade-ojfs in using low-lift airfoils for a 750-kilowatt stall-regulated wind turbine. Tip-region airfoils having a maximum-lift coefficient ranging from 0.7–1.2 were considered in this study, with the main objective of identifying the practical lower limit for the maximum-lift coefficient. Blades were optimized for both maximum annual energy production and minimum cost of energy using a method that takes into account aerodynamic and structural considerations. The results indicate that the effect of the maximum-lift coefficient on the cost of energy is small with a slight advantage to the highest maximum lift coefficient case considered in this study. As a consequence, higher maximum lift coefficient airfoils for the tip-region of the blade become more desirable as machine size increases, provided the airfoils yield acceptable stall characteristics. The conclusions are applicable to large wind turbines that use passive or active stall to regulate peak power.