Optimal Design of Wind Turbine Blades with Bend-Twist Couplings Effects

Abstract

This thesis concerns the optimal design of wind turbine blades for bend twist coupling effects. Bend-twist coupling effects can prove to be an effective way of reducing fatigue damage and root bending moments for a wind turbine blade. However, how can bend-twist coupling be incorporated into a wind turbine blade considering the many structural requirements? This thesis investigates the optimal design for bend-twist coupling in wind turbine blades. Gradient based
numerical optimization algorithms are applied to obtain composite material layups favorable for bend twist coupling. The thesis work builds a framework that allows for the selection of fiber angles at several sections along the blade, while considering structural constraints. This involves the use of a cross section analysis software and a finite element beam formulation for the evaluation of responses, while an aeroelastic software is used for load mitigation validation.
The structural constraints include tip twists and deflection, eigenfrequencies and material failure criteria of which the analytic sensitivities are calculated, implemented in the framework and validated against central finite difference gradient values. A simple cantilever sandwich beam is considered first as a trial for the framework and four problem formulations are defined to test both the framework and the considered optimization algorithms. A full scale wind turbine blade for a 10MW wind turbine is then subject for the optimization. A converged design for the full scale blade is obtained and subject to aeroelastic simulations in a steady state and turbulent inflow. From this, the load mitigation effects are observed and discussed. With the work done in this thesis project, a step closer to an effective framework for aeroelastic tailoring is achieved.