An overview of active load control techniques for wind turbines with an emphasis on microtabs



This paper outlines the benefits and challenges of utilizing active flow control (AFC) for wind turbines. The goal of AFC is to mitigate damaging loads and control the aeroelastic response of wind turbine blades. This can be accomplished by sensing changes in turbine operation and activating devices to adjust the sectional lift coefficient and/or local angle of attack. Fifteen AFC devices are introduced, and four are described in more detail. Non-traditional trailing-edge flaps, plasma actuators, vortex generator jets and microtabs are examples of devices that hold promise for wind turbine control. The microtab system is discussed in further detail including recent experimental results demonstrating its effectiveness in a three-dimensional environment. Wind tunnel tests indicated that a nearly constant change in CL over a wide range of angles of attack is possible with microtab control. Using an angle of attack of 5 degrees as a reference, microtabs with a height of 1.5%c were capable of increasing CL by +0.21 (37%) and decreasing CL by −0.23 (−40%). The results are consistent with findings from past two-dimensional experiments and numerical efforts. Through comparisons to other load control studies, the controllable range of this microtab system is determined to be suitable for smart blade applications. Copyright © 2009 John Wiley & Sons, Ltd.