Desirable Airfoil Characteristics for Large Variable-Speed Horizontal Axis Wind Turbines

In an effort to define the desirable airfoil characteristics for variable-speed wind turbines, a systematic study was performed using a series of five primary (75% station) and five tip (100% station) airfoils. The airfoils were designed to have similar aerodynamic properties, except for the amount of lift, which varied over a wide range. For several airfoil combinations, blade shapes weredesigned using the optimization code PROPGA together with PROPID, an inverse design method for HAWTs. It was not surprising to find that the higher lift airfoils resulted in lower solidity blades, but the variation in annual energy production differed by only 1% over the wide range considered. Roughness effects were also considered and are discussed. An approach to determine the best liftcoefficient distribution is discussed based on a new parameter termed the reduced Reynolds number.