STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable.

BACKGROUND

The present disclosure relates to wind turbines, and, more specifically, to winglets for retrofitting onto wind turbine blades.

Blade tip vortices emanating off the tip of a wind turbine blade during wind-driven movement leads to induced drag and reduced power generation in a wind turbine. In aircraft, winglets (also called wingtip devices) have been applied to reduce the generation of these tip vortices, thereby reducing induced drag. Similarly, winglets have been used at the tip of a wind turbine blade in order to improve power generation. Previous designs, however, have focused on large, heavy winglets aimed at increasing the power coefficient. The large, heavy winglets are bulky so that the winglets can withstand operational loads while reducing the effect of blade tip vortices. To withstand the added bending moments caused by the heavy winglets, the main blade must be structurally reinforced, resulting in significantly higher costs of retrofitting a winglet to a wind turbine blade.

SUMMARY

In one embodiment, the present disclosure relates a wind turbine having a main blade and a winglet. The main blade is arranged for wind-driven rotation in a vertical plane. The winglet extends from a tip of the main blade away from the vertical plane. The coefficient of power Cpof the main blade and winglet is at least 2% greater than a coefficient of power Cpof the main blade alone. A ratio of normal aerodynamic force generated by the winglet to centrifugal force generated by the winglet during rotation at a nominal speed is in a range between 0.75 and 2.

In another embodiment, the present disclosure relates to a winglet for retrofitting to a main blade of a wind turbine. The winglet includes a load bearing balsa spar, a foam core embedded with the spar, and a fiberglass skin over the spar. The winglet is configured to extend from a tip of the main blade away from a vertical plane of the main blade. A coefficient of power Cpof the main blade and winglet is at least 2% greater than a coefficient of power Cpof the main blade alone. A ratio of normal aerodynamic force generated by the winglet to centrifugal force generated by the winglet during rotation at a nominal speed is in a range between 0.75 and 2.

In yet another embodiment, the present disclosure relates to a method of designing a winglet for a wind turbine. The method includes the step of modeling aerodynamic and centrifugal forces of winglets having a range of configurations including winglet height, taper ratio, twist, and cant angle, wherein the winglet height, taper ratio, twist, and cant angle are used to define a grid in a Vector Lattice. The method further includes the step of determining a coefficient of power Cpof the winglet when applied to a predetermined main blade of the wind turbine. The method further includes the step of selecting a winglet configuration wherein a ratio of normal aerodynamic force generated by the winglet to centrifugal force generated by the winglet during rotation at a nominal rated speed is in a range between 0.75 and.

A further understanding of the disclosure will be obtained from the following detailed descriptions and accompanying drawings, which set forth illustrative embodiments that are indicative of the various ways in which the principals of the disclosure may be employed.

