Performance analysis of a small horizontal axis wind turbine under the use of linear/nonlinear distributions for the chord and twist angle

Abstract

The increase in efficiency, decrease in starting time, and ease in manufacturing of rotor blades are the most desirable aims of research in the design of small-scale wind turbines. A multi-objective optimization study is carried out to analyze the performance of a small horizontal axis wind turbine in terms of the output power and the starting time for four possible combinations of linear/nonlinear distributions of the chord length and twist angle along one-meter timber blades. The blade-element momentum theory is adopted for the calculation of the power coefficient and the starting time. The optimization is achieved through a genetic algorithm which simultaneously maximized the power coefficient and minimized the starting time. The most important contribution of this paper is the in-depth comparison of the linear and the nonlinear distributions for chord and twist angle subjected to the aforementioned optimization, which is not available in the existing literature in such detail. Results show that although the linear distributions have more deviation from the so-called ideal distributions, however, the output power performance of the blades with linear distributions is competitive with that of the nonlinear ones. Moreover, the results establish that the use of linear distribution can improve the starting performance at a lesser compromise of output power. This is of paramount importance, particularly to promote harnessing the wind energy in developing countries, as simpler distributions could facilitate the manufacturing of wind turbine blades. Apart from using the linear or nonlinear distributions for both the chord and the twist angle, two other cases are also investigated including the linear distribution for the chord and the nonlinear one for the twist and vice versa. The analysis of these cases shows that choosing the nonlinear distribution for the chord would improve the starting while using the linear one would lead to more powerful blades.