Wind Farm Control Methods - Yawing

The wake effect of yawing an upstream turbines is of interest in order to increase power production. In this study, the case of yawing is considered as asymmetric do to the tower and rotor rotation, and measurements have been performed in a wind tunnel. The rotational effects when yawing are obtained by investigating the difference between a disc and a rotor with the same drag and diameter. This is performed during a tower-symmetrical setup, and shows that the wake deflects approximately 1 radius for the disc and significantly less for the rotor at optimal tip speed ratio. The disc wake is similar to a jet shape in a crossflow and counter-rotating vortices are present, which is not the case for the rotor. Moreover, the differences between yawing in the different direction are investigated and show that for positive yaw-angles, the wake spreads more out and deflects more to the side and to the floor. Furthermore, for negative yaw-angles, the wake is located closer to downstream the rotor centre. These differences are slightly less present during shear flow conditions, in addition to a more sideways deflected wake