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Two-bladed wind turbines offer the potential for a lower cost of energy compared with three-bladed rotor turbines. This investigation was conducted to quantify the differences between the loads of upwind and downwind two-bladed wind turbines operating under random wind conditions. This paper focuses on a comparison of maximum and average loads that can cause first excursion failure, and loads that can cause fatigue failure. In this study, upwind and downwind turbines with two bladed rotors are compared. The NREL 5MW reference wind turbine was used as a baseline design and was modified as necessary to design a two bladed upwind wind turbine. The tower shadow effect was considered for the downwind turbine. The IEC61400-3 standard load cases were used to define the loading conditions for the wind turbine simulations. The computed load effects generally showed that the downwind configuration had lower load effects. Moreover, fatigue damage was lower for the two-bladed downwind turbine compared to the upwind turbine.

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A multidisciplinary design optimization (MDO) process of a large scale hybrid composite wind turbine blade is developed. Multiple objectives are considered in this design optimization: maximize length of blade, minimize weight and manufacturing cost. A wind turbine blade is divided into regions and the layup sequences for each region are considered as design variables. Applied load due to extreme wind condition for rotor rotation and rotor stop condition are considered for finite element analysis (FEA) to evaluate the structural strength. The structural stiffness is designed and illustrated so that the natural frequency of the blade does not coincidence with the excitation frequency of the wind turbine. A process of obtaining an optimum hybrid composite laminate layup and an optimum length of wind turbine blade is developed in this research.

In this study, load effects of identically rated power two- and three-bladed rotor wind turbines are computed and compared using the requirements of the IEC61400-3 standard. The two-bladed turbine includes a teeter mechanism. Moreover, an improved blade design is considered for the two-bladed turbine. A series of wind turbine operational simulations was performed for the wind turbine models under selected design load cases of IEC61400-3 standard. Loads were computed using the FAST code. The series of simulations were driven and post-processed using the FAST_SM code. Additionally, fatigue damages of the two- and three-bladed rotor wind turbines were computed. The study showed that the maximum load effects and fatigue damage of the two-bladed wind turbine generally increased compared to the three-bladed turbine. The simulation results also showed that the baseline design blade of the two-bladed wind turbine requires improvement in order to sustain the computed large load effects.