Passive Flow Control on Wind Turbine Rotors using Self-Adaptive Camber

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A load-dependent passive camber control concept featuring a mechanically coupled leading and trailing edge flap has been developed at the Institute of Fluid Mechanics and Aerodynamics at TU Darmstadt. Fluctuating inflow conditions lead to modified pressure distribution and induce a moment on the leading edge flap. The moment is transferred to the trailing edge flap in such a way that the clockwise rotation of the leading edge flap results in a counter clockwise rotation of the trailing edge flap. The resulting change in airfoil camber is completely passive and does not require sensors or control units. Its characteristics are determined solely by the fluid-structure interaction and the characteristics of the coupling mechanism. The concept is introduced for alleviating load fluctuations on wind turbine rotor blades with the overall goal of reducing fatigue and increasing rotor durability and turbine lifetime. During the first funding period, the functionality of the concept was proven under two dimensional inflow conditions in a wind tunnel.Inflow conditions in a rotating system differ fundamentally from the two dimensional case. Coriolis and Centrifugal forces provoke a radial redirection of the flow. The cross flow causes a difference of the pressure distribution compared to the two dimensional case. This proposal aims at investigating the adaptive camber concept under these modified inflow conditions: Rotor blades with adaptive camber mechanism will be developed and tested at the research turbine of PP2. In order to isolate the influence of crossflow from the fictitious forces, additional two-dimensional experiments with a swept wing will be performed. A second objective of this proposal is to guarantee operational safety at flow conditions differing from the design point. This is done by submitting a two-dimensional model with adaptive camber mechanism to high angle of attack fluctuations in the non-linear regime of the lift curve.