Operating modes of a teetered-rotor wind turbine

We examine the operating modes of a two-bladed teetered wind turbine the dynamics of which, because of the gyroscopic asymmetry of its rotor, can be quite distinct from the dynamics of a turbine with three or more blades. This asymmetry leads to system equations with periodic coefficients that are served using the Floquet approach to extract the correct modal parameters. The system equations are derived 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 dynamically instability. Under certain design conditions, yaw and teeter modal frequencies may coalesce.