Experimental study of a multielement airfoil for large wind turbines

Large wind turbines have thick airfoils at the root section of the wind turbine to support the weight of the blade and structural requirements, and aerodynamic efficiencies are in conflict near the root section of the blades. A four-element multielement airfoil system was tested as a replacement airfoil system for a thick single element airfoil near the root of a 10-MW scale conceptual wind turbine. The system consisted of a main element, two flaps, and a lower strut airfoil element for added structural support, and experiments were performed with the ability to move two flaps to any location relative to a main element. Tests were performed in the University of Illinois low turbulence subsonic wind tunnel with a chord length of approximately 1.5 feet (0.46 m) and a model span of approximately 2.8 feet (0.85 m). Results for the Reynolds number tested indicate that gap size should be no smaller than 2.5% system chord to avoid degradation in performance. A large overhang can adversely affect aerodynamic performance and lead to a loss of lift. Performance decreased if the strut was moved to any location other than the baseline condition. Results indicate that performance of high lift systems is more dependent upon the drag of the system than the high lift aerodynamics.