Search

In this work, the aerodynamic performance and optimization of a vertical-axis wind turbine with a high tip-speed ratio are theoretically studied on the basis of the two-dimensional airfoil theory. By dividing the rotating plane of the airfoil into the upwind and downwind areas, the relationship among the angle of attack, azimuth, pitch angle, and tip-speed ratio is derived using the quasi-steady aerodynamic model, and aerodynamic loads on the airfoil are then obtained. By applying the polynomial approximation to functions of lift and drag coefficients with the angle of attack for symmetric and asymmetric airfoils, respectively, explicit expressions of aerodynamic loads as functions of the angle of attack are obtained. The performance of a fixed-pitch blade is studied by employing a NACA0012 model, and influences of the tip speed ratio, pitch angle, chord length, rotor radius, incoming wind speed and rotational speed on the performance of the blade are discussed. Furthermore, the optimization problem based on the dynamic-pitch method is investigated by considering the maximum value problem of the instantaneous torque as a function of the pitch angle. Dynamic-pitch laws for symmetric and asymmetric airfoils are derived.

The design, analysis, and testing of an improved Shape Memory Alloy (SMA)-based tracking tab actuator is described in this paper. The goal of the actuator is to provide in-flight tracking capability for a helicopter rotor in order to minimize 1/rev vibrations due to rotor dissimilarities. Previous SMA-based actuator designs demonstrated the potential for in-flight rotor tracking but admitted drawbacks that led to inconsistent operation under air-loads. The current research builds upon the existing knowledge base and addresses the challenges encountered in previous designs. The objective is to achieve a deflection of ±5° with an accuracy of 0.10 under realistic aerodynamic loading conditions. The present actuation concept is based on the bidirectional motion of a pair of antagonistic SMA wires, with a passive friction brake to lock the tab position. A theoretical model of the actuator was developed based on Brinson's thermomechanical model. The model was used to predict the behavior of the actuator under external loading and applied as a design tool to identify optimal actuator parameters. The actuator was integrated into a NACA 0012 12in. chord blade section and tested in an open-jet wind tunnel at speeds of up to 120 ft/s (0.107 M) and at angles of attack up to 15°. Closed-loop tracking was implemented using a PID controller with gains selected by Ziegler-Nichols tuning. The improved SMA actuator meets the project goals by achieving repeatable tab deflection of up to ±5°with an average accuracy of 0.05°. Position hold under power-off conditions and a duty cycle of 20 cycles/h were also demonstrated. [ABSTRACT FROM AUTHOR]