STUDY OF THE TURBULENT CHARACTERISTICS OF THE NEAR-WAKE FIELD OF A MEDIUM-SIZED WIND TURBINE OPERATING IN HIGH WIND CONDITIONS

The near-wake turbulent structure that is downwind of a medium-sized, horizontal axis wind turbine at a distance of one rotor diameter is di scussed. The experimental site is the Samos Island Wind Park comprisin g nine wind turbines installed on the top of a 400 m-high saddle. The analysis is based on experimental data obtained mainly under strong wi nd conditions by two masts erected upstream and downstream of a wind t urbine. The field of wind turbulence is examined both in integral and spectral form. Consideration of the perturbation produced by the tower construction is crucial in the interpretation of results. Observation s show that the turbulent field varies from the edge to the center of the wake and strongly depends on the incident wind speed. Increased tu rbulent levels are observed near the blade tips, with evidence of a si milar trend around the hub height for all wind speeds. Decreases of wi nd turbulence are observed in mid frequencies inside the wake due to t he reduced shear associated with the flat crosswind velocity profile. This effect seems to dominate in the variation of the integral values of the longitudinal wind component variance. The low frequency portion of wind spectra reverses behavior in high wind speeds, i.e., an incre ase in energy relative to background values is observed. This is proba bly due to the shape of the turbine characteristic power curve. Cross- wind profiles of turbulent shear stresses at the lower boundary of the wake are also discussed.