Wake Effects on Middelgrund Windfarm


Title: Wake Effects on Middelgrund Windfarm
Publication Date:
July 01, 2003
Document Number: Risø-R-1415(EN)
Pages: 44

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Jørgensen, H.; Frandsen, S.; Vølund, P. (2003). Wake Effects on Middelgrund Windfarm. Report by Risø National Laboratory. pp 44.

This report describes the data analysis of the Middelgrund Wind Farm online collected data with the purpose of calculating the wake effects and turbulence intensities within the wind farm when maximum wake effects are present. The data are compared to the most commonly used wake model PARK implemented in Wasp 8.


In the analysis we have focused on the winds coming from North based on a Waspengineering analysis of the Middelgrund Wind Farm: The analysis shows that the directional change of the turbines with respect to the direction of turbine no 1 is nearly identical for the individual wind situations within a sector of 20 along the turbine array. The alignment of turbine no. 16 differs significantly from the others. In this analysis we cannot conclude whether this is a misalignment in the yaw angle measuring system or a real flow effect as calibration of the yaw angle system is only approximate.


The data analysis have been compared to a PARK calculation performed in Wasp 8. The PARK calculations have been converted from power to wind speed deficits and there is as substantial difference between the calculated defi-cits in wind speed between the data and the PARK model. However, it shall be noted that it is a very crude comparison since the lowest directional sector inter-val in the PARK/Wasp mode is 10° , and all events are assumed uniformly dis-tributed over this sector. Furthermore, the model does not include the changing direction of the wind flow through the turbine array caused by the interaction between the turbines and the flow. Finally the turbines are spaced by 2.6 rotor diameters, which is in the limit of the park model assumptions where the spac-ing is assumed to be higher than 5 rotor diameters.


Taking all this assumptions and model constraints into account the Park model overestimates the wind speed deficits with up to 30 % ,with an ever decreasing wind speed through the array when the wind is coming from north whereas a the data shows a tendency to a recovery of the wind through the array.


The turbulence intensity is enhanced up to 0.3 due to the wake effects. The analysis has shown that this enhancement is nearly independent of the number of turbines involved in the wake creation.

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