Spanwise Aerodynamic Loads on a Rotating Wind Turbine Blade

Wind turbine performance and load predictions depend on accurate airfoil performance data. Wind tunnel test data are typically used which accurately describe two-dimensional airfoil performance characteristics. Usually these data are only available for a range of angles of attack from 0 to 15 deg, which excludes the stall characteristics. Airfoils on stall-controlled wind turbines operate in deepstall in medium to high winds. Therefore it is very important to know how the airfoil will perform in these high load conditions. Butterfield et al. [1] have shown that three dimensional effects and rotation of the blade modify the two dimensional performance of the airfoil. These effects are modified to different degrees throughout the blade span. The Solar Energy Research Institute (SERI) hasconducted a series of tests to measure the spanwise variation of airfoil performance characteristics on a rotating wind turbine blade. Maximum lift coefficients were measured to be 200% greater than wind tunnel results at the 30% span. Stall characteristics were generally modified throughout the span. Lift characteristics were unmodified for low to medium angles of attack. This paper discussesthese test results for four spanwise locations.