Wind tunnel and rotation testing of a flexible trailing edge for wind energy turbine blades

Fatigue loads are becoming a limiting factor of modern wind energy turbines with increasing rotor diameters and hub heights. This applies especially to the blade root, where bending moments caused by cyclic loads, such as the vertical wind gradient, gusts, turbulence and other periodic inputs, reach their maximum value. Reducing these bending moments is therefore helpful to allow further growth of blade length and power rating of future turbines. One way to reduce these loads is provided by actively controlling the trailing edge at the outer part of the blade. This influences the lift and by this the root bending moment. In this paper, the experimental test results of a morphing, flexible trailing edge flap will be presented. The crucial advantage of the morphing mechanism consists in the possibility to keep the trailing edge completely sealed to the environment. This prevents the ingression of water, dust or insects which could cause excessive wear at the mechanism. This flexible trailing edge has been experimentally investigated within a wind tunnel and on a rotating test rig in real wind conditions. This paper will provide brief information about the design of the two-meter span test demonstrator, the instrumentation, and test setup. The main goal of both tests was the measurement of the flap polars to quantify the lift change caused by a deflection of the flexible trailing edge. In addition, a sensor controlled movement of the trailing edge was implemented in the rotation test with the aim to reduce the bending moment. Three different signals—the rotor azimuth, the angle of attack and the bending moment itself—have been used as a reference. The reduction of the bending moment could be demonstrated successfully for all three reference signals.