Yaw Rate, Rotor Speed and Gyroscopic Loads on a Small Horizontal Axis Wind Turbine

Abstract

The magnitude of gyroscopic rotor shaft and blade bending moments on a free yaw wind turbine rotor are proportional to the product of rotor speed and yaw rate. An analysis is presented of the relationship between these two variables and wind speed, based on field test data from a 2 m diameter wind turbine with a tail-fin furling system, and in reference to the recent revision of the International Electrotechnical Commission standard for small wind turbine design. Examples are given of fast yaw rates caused by furling, and by large wind direction changes at relatively small wind and rotor speeds. Analyses of data showed that reducing turbine yaw moment of inertia increases the magnitude of maximum yaw rate for a given rotor speed, and that yaw rate is highly influenced by tail fin aerodynamics.