Static aeroelastic optimization of composite wind turbine blades using variable stiffness laminates: Exploring twist coupled composite blades in stall control

There is a growth in the energy consumption of the world, leading to rapid depletion of natural resources, such as fossil fuels. Added to that, the environmental impact of fossil fuels (e.g. global warming) makes a renewable source of energy a better alternative for power generation. Among renewable energy sources, generating energy from wind is becoming more popular. Although the number of, installed, wind turbines is increasing rapidly, there are still many challenges ahead for making the cost of generating energy from offshore wind competitive with other energy sources. One method for making the Cost of Energy from wind competitive is to reduce the operational and maintenance cost of wind turbines. The operational and maintenance cost of wind turbines may be reduced by eliminating, as much as possible, rotating components of the turbine which are prone to wear and tear. An alternative way to regulate power is to use stall control scheme, thereby eliminating the need to use the pitch mechanism. With recent advances in composite technology for tailoring the structural response of composite structures, it is possible to apply the technique to the conventional passive stall control scheme. Particularly, the use of twist coupling for regulating (passively) the angle of attack, thus also the torque and power of the wind turbine, shows a promise to design adaptive blades for stall regulated wind turbines, with improved performance in terms of power and load control, as well as in terms of cost reduction. Most of the research conducted so far investigates the benefit of twist coupled blades for power and/or load regulation; either based on a parametric study using few design variables or using simplified models for analysing the aeroelastic response of adaptive blades. In this thesis, a detailed optimization study is performed using variable stiffness laminates, to evaluate the potential of twist coupled blades to enhance the aerodynamic performance of stall controlled wind turbines. Furthermore, detailed structural and aerodynamic constraints are included in the optimization study, while using an analysis tool with sufficient complexity to accurately capture the aeroelastic response of twist coupled blades.