Optimization study of the wind-turbine power coefficient using collective and cyclic pitch in yawed flow

Wind-turbine power output is a function of not only wind speed but of many other constraints such as attitude with respect to the wind and blade pitch settings. Maximizing a wind turbines power output is accomplished by operating at the system's optimal power coefficient with respect to these parameters. Previous research has shown that the maximum power produced is strongly affected by the wind direction, tip speed, pitch angle of the blades, and drag coefficient. In this paper, the objective is to optimize the power coefficient in a design space that includes variable collective and cyclic pitch in the presence of axial or yawed wind inflow. Wind turbines can use collective pitch or tower yaw to increase the optimal power coefficient when compared to a wind turbine with fixed blades. Hohenemser suggested the possibility of improved optimal performance in the presence of yawed inflow by means of active cyclic pitch. This paper presents a derived model for the aerodynamic performance of a wind turbine, a benchmark exercise to verify reasonable results, a case study to observe the results and then conclusions of the study. The results of the feasibility study support Hohenemser's hypothesis that increasing the control space of a wind turbine (from fixed pitch to the use of collective and cyclic pitch) increases the optimal power achieved for yawed inflow.