Abstract
In case of designing a horizontal-axis wind turbine rotor, especially for the purpose of high efficiency of energy conversion, it should be examined how the blade geometry be optimized and how the blade pitch angle be controlled for a specified geometry. In this paper, applying the momentum theory with PRANDTL's tip correction, an optimal aerodynamic design method for a wind turbine rotor at a given tip speed ratio is presented and the effects of section lift-to-drag ratio, activity factor and number of blades are investigated.
A quasi-optimization method for a linear taper blade is also proposed from a practical view point. Additional considerations are made with respect to the pitch control at the off-design range for large wind turbines. Two typical pitch control schemes of maximum and constant power modes are studied, which correspond to the control modes in the range over and below the rated wind speed, respectively. As a result, it is pointed out that a blade stall and a turbulent wake state may become the operational obstacles especially for high efficiency rotors.
