Experimental Study of the Transient Behavior of a Wind Turbine Wake Following Yaw Actuation

Abstract

Wind tunnel experiments were performed to investigate the response of a wind turbine model immersed in a replicated atmospheric boundary layer to dynamic changes in the yaw angle. Both the flow field in the wake and the operating properties of the turbine, namely its thrust force, torque, and angular velocity, were monitored during repeated yaw maneuvers for a variety of yaw angles. It was observed that the characteristic time scale of the transient experienced by the turbine scalar quantities was one order of magnitude larger than that of the yaw actuation and depended primarily on the inertia of the rotor and the generator. Furthermore, a Morlet wavelet analysis of the thrust signal showed a strong peak at the rotation frequency of the turbine, with the transient emergence of high activity at a lower frequency during the yaw maneuver. The insights provided by the proper orthogonal decomposition analysis performed on the wake velocity data enabled the development of a simple reduced-order model for the transient in the flow field based on the stationary states before and after the yaw maneuver. This model was then further improved to require only the final state, extending its applicability to any arbitrary wind farm as a dynamical surrogate of the farm behavior.