| Popis: |
A load-dependent passive camber control concept is introduced for alleviating load fluctuations on wind turbine rotor blades with the overall goal of reducing fatigue and increasing durability and turbine lifetime. The passive change of the camber line is realized through kinematically coupled leading and trailing-edge flaps. The leading-edge flap is actuated by the increased pressure forces due to the change in angle of attack. The trailing-edge flap is kinematically coupled to the rotation of the leading-edge flap. This combined motion results in an increase or decrease in airfoil camber dependent on the pressure difference along the airfoil and the restoring force applied at the leading-edge flap. This concept works fully passive, i.e. its characteristics are determined solely by the fluid-structure interaction. The quantification of these aerodynamic characteristics is the objective of the present study. The concept has been studied experimentally and numerically. The numerical simulations consider quasi-steady aerodynamics and the combined flap motion is described by one degree of freedom. The concept has been confirmed experimentally under quasi-steady conditions in the large scale low-speed wind tunnel at TU Darmstadt. The structural parameters which characterize the flap deflections are investigated systematically. The results show how the lift curve slope can be adjusted by the preload moment, the stiffness and the coupling ratio between the leading and trailing-edge flap. It is shown that it is possible to keep the lift coefficient constant due to the self-adaptive camber line. The numerical model is compared to the experimental results. The model is able to predict the effects revealed through the wind tunnel measurements. In the second part the numerical model of the airfoil section with leading and trailing-edge flaps is extended to consider also the bending and torsional degree of freedom. The results show that although the dynamic behavior of the blade changes significantly, load reduction is achieved and a flexible camber line is advantageous for the dynamic response of the rotor blade. Finally the concept is evaluated with the wind turbine simulator FAST. The underlying look-up tables are modified to incorporate the flapped airfoil characteristics. The results provide a baseline for the evaluation of the concept in conjunction with the aerodynamics encountered by wind turbines. |
