Aeroservoelastic modelling and active control of very large wind turbine blades for gust load alleviation.

Abstract

The increased flexibility of wind turbine blades necessitates not only accurate predictions of the aeroelastic effects, but also requires active control techniques to overcome potentially damaging loadings and oscillations. An aeroservoelastic model, capturing the structural response and the unsteady aerodynamics of very large rotors, will be used to demonstrate the potential of closed-loop load alleviation using aerodynamic control surfaces. The structural model is a geometrically-nonlinear composite beam, which is linearised around equilibrium rotating conditions and coupled with a linearised 3D Unsteady Vortex Lattice Method (UVLM) with prescribed helicoidal wake. This provides a direct higher fidelity solution to BEM for the dynamics of deforming rotors in attached flow conditions. The resulting aeroelastic model is in a state-space formulation suitable for control synthesis. Flaps are modeled directly in the UVLM formulation and LQG controllers are finally designed to reduce fatigue by about 26% in the presence of continuous turbulence. Trade-offs between reducing root-bending moments (RBM) and suppressing the negative impacts on torsion due to flap deployment will also be investigated.