AN EXPERIMENTAL-STUDY OF THE NEAR-WAKE STRUCTURE OF A WIND TURBINE OPERATING OVER COMPLEX TERRAIN

Wind parks are often cited in complex terrain whose features determine the wind flow over the area. Results from a field experiment, comprising in-situ and remote sensing techniques (high-resolution acoustic sounders), concerning the upwind area and the near-wake region behind a single medium-sized wind turbine are presented. The experimental site is the Samos Island Wind Park installed on top of a 390 m-high saddle. Because of the topography, wind speed acceleration and channeling effects are expected; thus, the commonly used logarithmic profile is not valid, and the choice of a representative surface roughness length z(o) is difficult. Interesting features of the profiles of the standard deviation of the ambient wind speed are also presented. The obtained results reveal a nonlinear interaction of the near wake with the turbine-tower shadowing, while cross-wind wake profiles indicate a potential core structure. The effect of ambient turbulence is apparent, especially at lower wind speeds, even at a distance of one rotor diameter (1 D) behind the turbine. The wake centerline at distances greater than 1 D is often observed at heights greater than the hub-height and attributed to the wind flow characteristics over the Wind Park. Finally, evidence of rotational motion inside the wake is identified.