Thomas Buhl

Wind Tunnel Test on Wind Turbine Airfoil with Adaptive Trailing Edge Geometry

,A wind tunnel test of the wind turbine airfoil Ris oe-B1-18 airfoil equipped with an Adaptive Trailing Edge Geometry (ATEG) was carried out. The ATEG was made by piezo electric actuators attached to the trailing edge of a non-deformable airfoil and controlled by an amplifier. The airfoil was tested at Re = 1.66x10 6 . Steady state and dynamic tests were carried out with prescribed deflections of the ATEG. The steady state tests showed that deflecting the ATEG towards the pressure side (posi tive β) translated the lift curve to higher lift values and deflecting the ATEG towards the suc tion side (negative β β β β) translated the lift curve to lower lift values. Furthermore, cd was almost unaffected by the ATEG actuation. Testing the airfoil for a step change of the ATEG f rom β=-3.0 to +1.8 showed that the obtainable Δcl was 0.10 to 0.13 in the linear part of the lift cu rve. Modeling the step response with an indicial function formulation showed that t he time constant in the step change and in sinusoidal deflections in dimensionless terms was T0* =0.6. Testing the ability of the ATEG to cancel out the load variations for an airfoil in si nusoidal pitch motion showed that it was possible to reduce the amplitude with around 80% from Δ Δ Δ Δcl=0.148 to Δcl=0.032.

Optimization of the Wind Turbine Rotor to Enhance the Performance

In this paper the structural layout of wind turbine blades are optimized in the context of reducing blade fatigue loads. A two-level optimization approach where each level of optimization has a different purpose is introduced. In this paper, only the upper-level optimization is performed. Before initiating the optimization process, fatigue load analysis of normal production with normal turbulence model (DLC 1.2) is performed to select the most severe operating case of the wind turbine for the blade fatigue loads. At the upper-level, preoptimization is conducted before running the main upper-level optimization process in order to reduce the considered number of cross-section by which the whole blade structural properties along the blade are represented. It results in saving the time cost without losing computational accuracy. Decreasing flapwise fatigue loads is selected as an objective for the upper-level, by changing blade structural properties such as mass, flapwise stiffness, edgewise stiffness, and torsional stiffness. The maximum blade tip deflection and edgewise blade fatigue loads are considered as constraints to be kept below the original values. As an optimizer, one of the gradient based methods, fmincon in MATLAB, is utilized. The 5MW NREL reference wind turbine is considered as an objective turbine. For the aeroelastic analysis and the computation of equivalent fatigue loads, simulations using the non-linear aeroelastic multibody code ,HAWC2, are conducted and the rainflow counting methodology is used. Optimized results obtained for the upper-level show not only a reduction of 13% on the equivalent fatigue load in flapwise direction but also reductions of 26%, 16%, and 18% on the equivalent fatigue load in edgewise direction, total blade mass, and maximum tip deflection, respectively.