A procedure to redesign a comparable blade structure of a two-bladed turbine based on a three-bladed reference

Abstract

Two-bladed turbines might be an alternative for future offshore wind turbine installations due to the promising opportunity to be more economical compared to three-bladed turbines. Looking at the rotor blades, two-bladed turbines with a comparable design either rotate 22.5% faster or have up to 50% increased chord lengths. The latter result in a significantly higher second moment of area, which enables rotor mass savings and thus fewer costs while withstanding ~50 % higher flapwise loads per blade. Unfortunately, such a design could also cause buckling issues. Increasing the design tip speed reduces stability issues but lowers the rotor mass savings. Consequently, the challenging task is to find an optimal compromise between preventing buckling and saving rotor mass, and thus to ensure a fair comparison of two- and three-bladed turbines’ blades. To overcome this challenge, a procedure for redesigning a comparable blade structure is introduced. The procedure is exemplarily demonstrated for large 20 MW offshore wind turbines. Compared to the three-bladed reference, the overall rotor mass reduction of the two-bladed turbine is 13.5 % for the most beneficial compromise detected. Simultaneously, the blades showing good accordance with the reference concerning static stresses and buckling characteristics under their respective loads.