Analysis of alternative adaptive geometrical configurations for the NREL-5MW wind turbine blade

Abstract

The correct prediction of flexo-torsional deformation is of capital importance for the future development of advanced wind-turbine blade prototypes. Coupling between bending and twisting can be used to reduce extreme loads and improve fatigue performance. This is the principle of the adaptive blades, where the incremental loads are reduced when, as the blade bends, the flexo-torsional modes of the blade structure produce a change in twist, and so in the angle of attack, modifying the lift force acting on the blade sections. Bend-twist coupling could be achieved either by modifying the internal structure (structural adaptiveness), or by readapting the geometry of the blade (geometrical adaptiveness). These two techniques can be used independently or combined, complementing each other. We have developed a novel computational tool for the aeroelastic analysis of wind-turbine blades, which allows a full representation of the flexo-torsional modes of deformation of the blade as a complex structural part and their effects on the aerodynamic loads. In this paper, we report some recent results we have obtained applying our code to the analysis of geometrical adaptive blades, taking full advantage of the coupled deformation modes that our aeroelastic code can represent. We analyze alternative blade configurations for the NREL-5 MW wind-turbine, optimizing the design to mitigate vibration and improve fatigue performance.