Aerodynamic Tests of Darrieus Wind Turbine Blades

Abstract

An indoor facility for the aerodynamic testing of Darrieus turbine blades was developed. Lift, drag, and moment coefficients were measured for two blades whose angle of attack and chord-to-radius ratio were varied. The first blade used an NACA 0015 airfoil section; the second used a 15% elliptical cross section with a modified circular arc trailing edge. Blade aerodynamic coefficients were corrected to section coefficients for comparison to published rectilinear flow data. Although the airfoil sections were symmetrical, moment coefficients were not zero and the lift and drag curves were asymmetrical about zero lift coefficient and angle of attack. These features verified the predicted virtual camber and incidence phenomena. Boundary-layer centrifugal effects were manifested by discontinuous lift curves and large differences in the angle of zero lift between the NACA 0015 and elliptical airfoils. It was concluded that rectilinear flow aerodynamic data are not applicable to Darrieus turbine blades, even for small chord-to-radius ratios. Nomenclature b, C = blade span and chord ci>cd>cm = section li ft, drag, and moment coefficient CL, CD, CM = blade lift, drag, and moment coefficient cl , CL = section and blade lift curve slope, per degree Cp a = rotor power coefficient, the ratio of power extracted to energy theoretically available in the wind Cu = circulation control blowing coefficient