Isogeometric framework for aeroelastic wind turbine rotor analysis

Kurzfassung

An isogeometric framework is presented for parametrizing a wind turbine rotor blade and analysing its response. The framework consists of multi-fidelity approach for wind turbine rotor analysis. The aeroelastic loads are determined using a low-fidelity model. This low-fidelity model is based on isogeometric approach to model both the structural and aerodynamic properties, because of its suitability for shape and size optimization. The structural properties are determined using a geometrically exact beam model and a standard Blade Element Momentum(BEM) method is used to calculate the aerodynamic loads. In addition, the aerodynamic loads calculated using BEM theory are modified to account for change in the blade shape during shape optimization or for very flexible blade undergoing large deformation. The cross-sectional properties of the blade, needed for the beam model, are determined using an in-house tool that generates the cross-sectional stiffness properties with all possible couplings for thin-walled, multi-cell, open or closed cross-sections with anisotropic properties. The aeroelastic loads are applied in finite element analysis (Nastran) as static loads to a shell model of the blade; and both the stress response and buckling response are extracted. In addition, sensitivity coefficients of the aeroelastic responses to the design variables are calculated, such that this framework can also be used to optimize the rotor blade. Furthermore, the capabilities of Nastran are extended such that design dependent loads can be applied, resulting in correct aeroelastic sensitivities of Nastran responses. The framework is verified against results from the commercial codes FAST and GH Bladed, using the NREL 61.5 m rotor blade as a baseline for comparison,showing good agreement. Finally, the capability of the present method in designing and analysing non-conventional blades is demonstrated by investigating the aeroelastic characteristics of the curved Sandia 30m, STAR blade.