Author's School

School of Engineering & Applied Science

Author's Department/Program

Mechanical Engineering and Materials Science

Language

English (en)

Date of Award

5-24-2012

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Chair and Committee

David Peters

Abstract

Wind turbine power output is a function of not only wind speed but many other constraints such as attitude with respect to the wind and blade pitch settings. Optimizing power output with respect to these parameters is accomplished by optimizing the rotary system's power coefficient. A primary objective of this research is to optimize the power coefficient in a design space that includes collective and cyclic pitch in the presence of axial or yawed wind inflow. The model developed to perform this analysis uses blade element theory and a nonlinear version of the Pitt Peters dynamic inflow model. The model was compared to the National Renewable Energy Labs WT_Perf wind turbine simulation and showed an acceptable match for the domain being analyzed. A secondary objective of this research is to investigate the effect of continuous cyclic pitch on the power coefficient when used to control the instantaneous moments of a wind turbine at a specific yaw angle with respect to the wind. Wind-turbine power output and attitude with respect to the wind is generally controlled through collective pitch and\or tower yaw, via a vane or actuator. Hohenemser suggested the possibility of control by means of rotor yaw via moments generated by cyclic pitch.: Wind turbines generally do not have cyclic pitch). For the purposes of this dissertation, the investigation focuses on the feasibility of Hohenemser's idea by evaluating the change of the optimal power coefficient when cyclic pitch is also being used to reduce the magnitude of the system's instantaneous moments. Collective blade pitch control is an accepted practice to optimizing power output by setting the turbine to the optimal collective pitch settings as the wind magnitude changes. This research shows that the extension of using cyclic pitch can further increase the optimal power coefficient by using optimal values for collective and cyclic pitch in yawed inflow conditions. Secondly this research supports the feasibility of Hohenemser's idea that cyclic pitch can be used to simultaneously optimize the power coefficient and minimize the instantaneous moments in yawed inflow. The results present numerical values for the optimal collective and cyclic pitch values that can optimize the power coefficient and keep the system moments below a design threshold. The results also show that the optimal power coefficient is not seriously degraded when cyclic pitch is both minimizing system moments and optimizing the power coefficient.

Comments

Permanent URL: http://dx.doi.org/10.7936/K75T3HJK

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