Applications of Low-Speed Dynamic-Stall Model to the NREL Airfoils

Abstract

National Renewable Energy Laboratory, USA (NREL) airfoils have been specially developed for wind turbine applications, and projected to yield more annual energy without increasing the maximum power level. These airfoils are designed to have a limited maximum lift and relatively low sensitivity to leading-edge roughness. As a result, these airfoils have quite different leading-edge profiles from airfoils applied to helicopter blades, and thus, quite different dynamic-stall characteristics. Unfortunately for wind turbine aerodynamics, the dynamic-stall models in use are still those specially developed and refined for helicopter applications. A good example is the Leishman–Beddoes dynamic-stall model, which is one of the most popular models in wind turbine applications. The consequence is that the application of such dynamic-stall model to low-speed cases can be problematic. Recently, some specific dynamic-stall models have been proposed or tuned for the cases of low Mach numbers, but their universality needs further validation. This paper considers the application of the modified dynamic low-speed stall model of (“A Modified Dynamic Stall Model for Low Mach Numbers,” 2008, ASME J. Sol. Energy Eng., 130(3), pp. 031013) to the NREL airfoils. The predictions are compared with the data of the NREL airfoils tested at the Ohio State University. The current research has two objectives: to justify the suitability of the low-speed dynamic-stall model, and to provide the relevant parameters for the NREL airfoils.