On the structural response of two- and three-bladed vertical axis wind turbines

Vertical axis wind turbines have suffered from the periodic nature of the aerodynamic loads and early efforts at commercialization were plagued by fatigue issues resulting from an inability to anticipate critical resonances. This paper examines the criteria for determining whether intersections of harmonics of the rotor speeds and natural frequencies will be damaging in two‐ or three‐bladed machines. The approach involves expressing the complex natural modes and also the aerodynamic loads and structural response as components of the real, stationary modes. The results show that the symmetry offered by three‐bladed rotors leads to many intersections being benign whereas the two‐bladed rotor does not benefit in this way.