Wind Turbine Blade Design Optimization for Reduced LCoE, Focusing on Design-Driving Loads Due to Storm Conditions

Design modifications of the blade inner structure, targeted at reducing design-driving extreme loads due to storm conditions, are assessed in the present paper. Under survival wind speeds, the lack of sufficient aerodynamic damping in the edgewise direction is responsible for excessive stall-induced vibrations that usually drive wind turbine blade design loads. The modifications considered in the work are (i) a non-symmetric increase in the thickness of the uniaxial and tri-axial material on the suction and pressure side of the blade sections, (ii) a shift in the spar caps in opposite directions and (iii) the ply-angle re-orientation of the laminates on the spar caps. The first two design interventions aim at increasing the damping of the low-damped edgewise modes in the idling rotor, while the third aims at reducing the fatigue and ultimate loads in normal operation. The design parameters in the problem are determined on the basis of a multidisciplinary optimization (MDAO) process, which minimizes the levelized cost of energy (LCoE). The in-house integrated optimization tool employed in the present study combines: (i) a servo-aero-elastic analysis tool for calculating ultimate loads and power yield, (ii) a cross-sectional analysis tool for obtaining structural properties and stress distributions in the modified blades and (iii) a cost model of the overall wind turbine to evaluate the LCoE.