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A comparative laboratory and full-scale study of the near wake structure of a wind turbine

Helmis, C.G., Whale, J.ORCID: 0000-0002-3130-5267, Papadopoulos, K.H., Anderson, C.G., Asimakopolous, D.N. and Skyner, D.J. (1994) A comparative laboratory and full-scale study of the near wake structure of a wind turbine. In: Proceedings of the 5th European Wind Energy Association Conference, 10 - 14 October, Thessaloniki, Greece pp. 465-471.

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The operation of a wind turbine produces a downstream region of reduced wind speed, the so-called wake. The wake constitutes an important factor in determining the siting of turbines in wind farms. The mean wake characteristics, and their relation to the incident wind field and the local topography, are of primary importance for the estimation of available wind energy. The turbulent structure of the wake affects the loading and fatigue of downstream turbine rotors, and dictates the minimum spacing of the machines within a wind fam. In order, then, to achieve satisfactory performance from wind farms, especially in areas of complex terrain, a detailed knowledge of the above wake parameters is required.

The present paper describes a recent investigation into the properties of the wake of a three-bladed wind turbine. Measurements were made on both a full-scale machine, and on a replica model in the laboratory, at approximately 1/100 scale. The full-scale experiments were carried out on the Greek island of Samos, by workers from the University of Athens, and were based on comprehensive anemometry measurements. The small-scale experiments were conducted by a research group at the University of Edinburgh, Scotland, using the relatively new technique of particle image velocimetry (PIV).

A major objective of the work was to assess the validity of small-scale PIV measurements as a tool for investigating full-scale wind turbine phenomena. If successful, there would be significant attractions in using the PIV method, due to its ability to map the velocity in the entire rotor wake at a given instant PIV vector maps may be processed to yield both bulk wake measurements, such as velocity deficits, or data relating to the detailed structure of the wake, e.g. vorticity measurements. In the present campaign, velocity ratios measured 1.1 diameters (D) downstream of the rotor, ie. in the near wake, were compared, using data from full-scale and model scale.

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