Development of a model to investigate the yaw behaviour of small horizontal axis wind turbines

Almost all small wind turbines have a tail vane to point the wind rotor into the wind direction. Various types of control mechanisms are used to protect the wind turbines from high-wind speeds. In this study, a generic model of a wind turbine is developed to investigate the yaw operation of small-scale horizontal axis wind turbines (HAWT) with a single tail vane. A tilt-up wind turbine is considered here as most of the other HAWT types can be simplified to a state of this model. In the tilted up wind turbines, the wind rotor is free to move around the horizontal axis as well as the vertical one. When the wind speed exceeds the rated value, the wind rotor tilts upwards, taking up a stable position with an inclination towards the direction of the wind, thus controlling the wind component responsible for power generation. This article describes the development of a mathematical model of small-scale HAWT using the D'Alembert's principle to investigate the complex behaviour of the wind turbine under transient and steady-state operating conditions. In this model, the blade element theory was adapted to predict the aerodynamic forces on the wind rotor at each rotor position. Combining the modified blade element with the momentum theories makes it possible to evaluate flow fields of induced velocities around the wind rotor. Yaw movements are modelled by considering dynamic responses of the tail vane. Finally, simulation results are presented to illustrate the yaw behaviour of a small wind turbine.