Optimization of the Wind Turbine Rotor to Enhance the Performance

Abstract

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.