In-Blade Measurements of Cyclic Loading on Yawed Turbines with Trailing Edge Flap

Abstract

Wind turbines operate predominantly in relatively unsteady flow conditions and are typically misaligned with the incoming wind. Based on the literature review, controlling a section of the trailing edge of the turbine blade is found to reduce load fluctuations on wind turbine blades. Here, a detailed experimental setup describes a 3.5 m diameter wind turbine equipped with a trailing edge flap (TEF). The instrumentation of the compact blade was capable of measuring surface pressure and root bending moment, as well as controlling a TEF simultaneously and in time-resolved fashion. The blade is of constant pitch and chord of 178 mm while the TEF covers 20% of the chord and 22% of the 1.47 m aerodynamic blade span. The turbine was tested in a controlled wind generation facility large enough to house the turbine with less than 7% blockage. The wind turbine was tested for a range of tip speed ratios, blade pitch angles, flap angles and yaw cases. Although the turbine blade is capable of cyclically and dynamically change the blade pitch and flap angle, this paper only investigates constant pitch and flap angles. The results show that changes to the flap or pitch angle are capable of manipulating the coefficient of power, root bending moment and normal force coefficient. The results also show that the flap demonstrates similar control authority to that of the pitch system with the flap occupying just 4% of the blade surface area without reducing the power output of the turbine.