Operating Modes of a Teetered-Rotor Wind Turbine

We examine the operating modes of a two-bladed teetered wind turbine. Because of the gyroscopic asymmetry of its rotor, this turbine's dynamics can be quite distinct from those of a turbine with three or more blades. This asymmetry leads to system equations with periodic coefficients that are solved using the Floquet approach to extract the correct modal parameters. The system equations arederived using a simple analytical model with four degrees of freedom: nacelle yaw, rotor teeter, and flapping associated with each blade. Results confirm that the turbine modes become more dominated by the centrifugal and gyroscopic effects as the rotor speed increases. The gyroscopic effect may also cause dynamic instability. Under certain design conditions, yaw and teeter modal frequencies maycoalesce.