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ECN publication
ECN test farm measurements for validation of wake models
Published by: Publication date:
ECN Wind Energy 14-5-2007
ECN report number: Document type:
ECN-M--07-044 Conference Paper
Number of pages: Full text:
12 Download PDF  

Presented at: European Wind Energy Conference 2007, Milan, Italy, 7-10 mei 2007.

Measurement results are presented from the EWTW test farm of ECN consisting of five 2.5 MW turbines in a row and a meteorological measurement mast of 108 m height. The data cover a period of about 2 years and are gathered for the validation of models for wake simulation and farm design. The results presented in this paper comprise: - farm performance for wind directions at small angles with the row, - performance of the individual turbines in the row up to quadruple wake conditions, - performance of a turbine in single wake conditions at regular and double rotor distance (3.8D and 7.6D), - turbulence intensities and turbulence ratios in single wakes at 2.5D and 3.5D distance behind the rotor. The results show that with wind directions at angles of about 25° with the farm orientation the leeward turbines produce more power than the 1st turbine and that the difference increases downwind up to 14%. Striking and unexpected results are similar maximum performance deficits in single wakes at 3.8D and 7.6D and very low turbulence intensities and a "hat shaped" velocity profile in the single wake at 2.5D. The measured wind velocity profiles in the wake have been compared with preliminary numerical simulations of ECN’s WAKEFARM program. This program can be characterised as a parabolised k-? turbulence model. A well known problem of such parabolised wake codes is that they commonly account the near wake by means of a very uncertain empirical initialisation. The present model accounts the near wake through results from a physical model. The width of the wake was very well predicted and fair agreement with the magnitude of the velocity deficit was observed. The turbulence in the wake directly behind the rotor is not well predicted.

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