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An Experimental Investigation of Wind-farm Flows
KTH, School of Engineering Sciences (SCI), Mechanics.
2014 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

In this thesis, fundamental properties of the turbulent ow above di erent wind-farm models were determined by means of wind-tunnel measurements. The assessed wind farms consisted in two staggered congurations, and two inline congurations, where two di erent streamwise spacings were evaluated. The experiment was focused on dense wind farms: the spacing in the spanwise direction was xed to approximately 3d (where d indicates the rotor diameters) for every case, and two streamwise spacings were used: 2.5d and 5d. Freelyrotating turbines were used to perform this experiment. The wind-turbine models had a diameter of 45 mm and a height of 85 mm from the ground to the top tip. The wind-farm models were placed one at a time inside the test section of the KTH NT2011 wind tunnel, where the inow was completely at, i.e there was no simulated atmospheric boundary layer. X-wire anemometry was the measurement technique to measure the streamwise and wall-normal velocities above the wind farms. From the results, it could be observed that close to the turbines, the streamwise mean velocity had variations in the spanwise direction for inline and staggered congurations, even deep downstream on the wind farms. Horizontal averages were applied to the data to account for the inhomogeneity of the properties above the wind farms. A scaling behaviour was found on the ow above all the wind farms studied: in order to have the streamwise mean velocity prole, all that was needed was the boundary layer thickness, the free-stream velocity, and the streamwise velocity close to the top tip of the turbines. Other scaling behaviours were found for the Reynolds stresses. The dispersive stresses above di erent wind farms did not scale with the friction velocity, since it was seen that these stresses are highly dependent on the wind farm layout. Therefore, it was concluded that Reynolds stresses and dispersive stresses cannot be compared to each other because they come from di erent scales: the small scales and the large velocity scales, respectively. An equation to estimate the friction velocity above wind farms was derived, requiring measurements of the angular velocity of the turbines, the free-stream velocity, and the mean velocities close to the tip of the turbines. Finally, it was found that the angular velocity of the turbines was 25 % higher for the staggered arrangement, when comparing it with an inline wind farm.

Place, publisher, year, edition, pages
2014. , 82 p.
National Category
Engineering and Technology
URN: urn:nbn:se:kth:diva-170785OAI: diva2:839881
Educational program
Master of Science - Aerospace Engineering
Available from: 2015-08-04 Created: 2015-07-06 Last updated: 2015-08-04Bibliographically approved

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