Potential load reductions on megawatt turbines exposed to wakes using individual-pitch wake compensator and trailing-edge flaps

Wind turbines located in wind farms experience inflow wind conditions that are substantially modified compared with the ambient wind field that applies for stand-alone wind turbines because of upstream emitted wakes. This has implications not only for the power production of a wind farm, but also for the loading conditions of the individual turbines in the farm.

The dynamic wake meandering model (DWM) is believed to capture the essential physics of the wake problem, and thus, both load and production aspects can be predicted, which is contrary to the traditional engineering wake prediction methods that typically focus on either load or power prediction. As a consequence, the wake affected inflow field generated by the DWM formulation opens for control strategies for the individual turbine.

Two different control approaches for load reduction on the individual turbines are implemented in the multi-body aero-servo-elastic tool HAWC2, developed at Risø-DTU in Denmark, and their potential load reduction capabilities compared: (1) full-blade ‘individual-pitch controllers’ acting as wake compensators and (2) controllers using trailing-edge flaps.

Information on the wake inflow conditions, induced by upstream turbines, is extracted from measurements of the blade-root bending moment and/or one-point recordings of flow angle of attack to the blades (pitot tube) measurements. In the former implementation, the pitch angle of each blade is compensated for as an addition to the collective-pitch, rotor-speed control.

In the latter implementation, the (uniform) flap deflection angle is dictated by the particular controller version in question. Copyright © 2010 John Wiley & Sons, Ltd.