Optimal Design of a Simplified Morphing Blade for Fixed-Speed Horizontal Axis Wind Turbines

Abstract

The aim of designing the wind turbine blades is to improve the power capture ability. Since the rotor control technology is currently limited to controlling the rotor rotational speed and the pitch of the blades, an increasing concern has been given to the morphing blades. In this paper, a simplified morphing blade is introduced, which has a linear twisted distribution along the span and its shape can be controlled by adjusting the root twisted angle and the tip twisted angle of the blade. Moreover, to evaluate the performances of the wind turbine blades, a numerical code based on the blade element momentum theory is developed and validated. The blade of the NREL Phase VI wind turbine is taken as a reference blade, and the optimization problems associated with the morphing blade and pitch control blade are both formulated. The optimal results show that the morphing blade gives better results than the pitch control blade in terms of produced power. Under the assumption that in a given site, the annual average wind speed is known and the wind speed follows the Rayleigh distribution, we can evaluate the annual energy produced by these three blade types. While the annual average wind speed varies from 5 m/s to 15 m/s, the results show that the optimal morphing blade can increase 23.9 percent to 71.4 percent in annual energy production while the optimal pitch control blade can increase 22.5 percent to 67.4 percent in annual energy production, over the existing twisted pitch fixed blade.