Design of Large Wind Turbines using Fluid-Structure Coupling Technique

Aerodynamic and structural dynamic performance analysis of modern wind turbines are routinely carried out in the wind energy field using computational tools known as aero-elastic codes. Most aero-elastic codes use the blade element momentum (BEM) technique to model the rotor aerodynamics and a modal, multi-body, or finite-element approach to model the turbine structural dynamics. A novel aeroelastic code has been developed called MIRAS-FLEX. MIRAS-FLEX is an improvement on standard aero-elastic codes because it uses a more advanced aerodynamic model than BEM. MIRAS-FLEX combines the three-dimensional viscous-inviscid interactive method, MIRAS, with the dynamics model used in the aero-elastic code FLEX5. Following the development of MIRAS-FLEX, a surrogate optimization methodology using MIRAS alone has been developed for the aerodynamic design of wind-turbine rotors. Designing a rotor using a computationally expensive MIRAS instead of an inexpensive BEM code represents a challenge, which is resolved by using the proposed surrogate-based approach. The approach is unique because most aerodynamic wind-turbine rotor design codes use the more common and inexpensive BEM technique. As a verification case, the methodology is applied to design a model wind-turbine rotor and is compared in detail with the one designed with BEM. Results demonstrate the methodology is effective for the aerodynamic design of wind-turbine rotors. To perform more realistic large wind-turbine rotor designs, a structural design code was needed. Such a structural design code has been developed to minimize the cost of energy (COE) of the NREL 5MW wind-turbine blade. Blade stiffness and mass are computed using the NREL PreComp code based on the classical laminate theory, while blade natural frequencies are obtained from the NREL BModes code. The aero-elastic program FLEX5 computes loads based on design load cases from the IEC standards, which are then used to compute the deflections, strains, and buckling constraints. The minimum COE is found by implementing the procedure with a gradient-based optimizer and using the wind turbine design cost and scaling model of NREL. Last, a unique framework to design large wind-turbine rotors has been developed by combining MIRAS-FLEX, the surrogateoptimization code, and the structural design code. The optimization framework was used to design large wind turbine blades using both FLEX5 and MIRAS-FLEX with good results obtained.