Composite optimization of wind turbine blades using a lamination parameter based framework

Abstract

The design of wind turbines has progressively evolved over recent decades as part of an ongoing effort to provide economically competitive solutions for wind energy production. In particular, rotors have increased in size so as to capture more wind energy while limiting installation costs. At the same time blade designers have had to continually improve the structural efficiency of blades in order to accommodate higher extreme loads resulting from growing rotor diameters. The research presented in this study focuses on an improvement of structural fidelity of a 7.5-MW wind turbine rotor blade based on the SmartBlades1 project reference blade. The framework used for the study relies on a compact and continuous parameterization of the blade structures in order to enable gradient-based optimizations. This parameterization is achieved by using lamination parameters as design variables for the optimization. This replaces the heavy and cumbersome standard approach relying on laminate stacking sequences while also offering great tailoring capabilities. The formulation and implementation that enable the structural design and optimization of the rotor with this parametrization are detailed. The objective function to be minimized is the blade skin weight. The model includes various design constraints: strains and buckling, and the design variables are: structural thicknesses and lamination parameters. The optimization was carried out on both the monolithic type and sandwich type blades and the results compared. The in-house aero-elastic program TurbLoads computes loads based on design load cases from the IEC standards and was used to simulate more comprehensive aerodynamic loading in this study. A study was carried out to investigate the influence of flexibility on the loads. It was found that quasi-rigid and flexible loads do not change much for the optimized monolithic blade.