A comparison of lab-scale free rotating wind turbines and actuator disks

Abstract

Planar particle image velocimetry was conducted upstream and in the near-wake of a lab-scale free-rotating wind turbine model and compared to several actuator disks with the same dimensions. The Reynolds number of the incoming flow is order 104. Actuator disks with different designs and solidities were tested, and the process of actuator disk selection is explicitly shown. The drag, mean velocity and mean vorticity in the wake of the disks were compared to that of the rotating model. For the disk that was the best match, the Reynolds stresses and swirling strength are also presented. The instantaneous swirling strength illustrated that despite similar mean fields, the instantaneous phenomena were significantly different. Distinct tip vortices were present in the wake of the rotating model but were absent from the wake of the actuator disk. Proper orthogonal decomposition was used to further investigate the underlying phenomena in the two flows, again demonstrating the importance of tip vortices when studying the rotating model and the lack of such distinct vortices when using the actuator disk. Hence, despite well-matched mean characteristics, the instantaneous structures in the two flows remain distinct.