Aerodynamic characteristics of wind turbine blade airfoils at high angles-of-attack

Airfoil characteristics at deep stall angles were investigated. It appeared that the maximum drag coefficient as a function of the airfoil upwind y/c ordinate at x/c=0.0125 can be approximated by a straight line. The lift-drag ratios in deep stall of a number of airfoils with moderate lower surface thickness coincide. It was found that the lift-drag ratio of airfoils with leading edge separation is independent of aspect ratio. The lift-drag ratios of the various sections of a non-rotating and a rotating blade in deep stall coincide with the two-dimensional curve.