Journal cover Journal topic
Wind Energy Science The interactive open-access journal of the European Academy of Wind Energy
Wind Energ. Sci., 2, 285-294, 2017
http://www.wind-energ-sci.net/2/285/2017/
doi:10.5194/wes-2-285-2017
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research articles
29 May 2017
Why the Coriolis force turns a wind farm wake clockwise in the Northern Hemisphere
Maarten Paul van der Laan and Niels Nørmark Sørensen Technical University of Denmark, DTU Wind Energy, Risø Campus, Frederiksborgvej 399, 4000 Roskilde, Denmark
Abstract. The interaction between the Coriolis force and a wind farm wake is investigated by Reynolds-averaged Navier–Stokes simulations, using two different wind farm representations: a high roughness and 5 × 5 actuator disks. Surprisingly, the calculated wind farm wake deflection is the opposite in the two simulations. A momentum balance in the cross flow direction shows that the interaction between the Coriolis force and the 5 × 5 actuator disks is complex due to turbulent mixing of veered momentum from above into the wind farm, which is not observed for the interaction between the Coriolis force and a roughness change. When the wind farm simulations are performed with a horizontally constant Coriolis force in order to isolate the effect of the wind veer, the wind farm wake deflection of the 5 × 5 actuator disks simulation remains unchanged. This proves that the present wind veer deflects the wind farm wake and not the local changes in the Coriolis force in the wake deficit region. An additional simulation of a single actuator disk, operating in a shallow atmospheric boundary layer, confirms that the Coriolis force indirectly turns a wind turbine wake clockwise, as observed from above, due to the presence of a strong wind veer.

Citation: van der Laan, M. P. and Sørensen, N. N.: Why the Coriolis force turns a wind farm wake clockwise in the Northern Hemisphere, Wind Energ. Sci., 2, 285-294, doi:10.5194/wes-2-285-2017, 2017.
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Short summary
In recent years, wind farms have grown in size and are more frequently placed in wind farm clusters. This means that large-scale effects such as the interaction of the Coriolis force and wind farm wakes are becoming more important for designing energy efficient wind farms. The literature disagrees on the turning direction of a wind farm wake due to the Coriolis force. In this article, we explain why the Coriolis force turns a wind farm wake clockwise in the Northern Hemisphere.
In recent years, wind farms have grown in size and are more frequently placed in wind farm...
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