Volume 3, issue 1 | Copyright

Special issue: Wind Energy Science Conference 2017

Wind Energ. Sci., 3, 293-300, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research articles 24 May 2018

Research articles | 24 May 2018

How does turbulence change approaching a rotor?

Jakob Mann, Alfredo Peña, Niels Troldborg, and Søren J. Andersen Jakob Mann et al.
  • DTU Wind Energy, Technical University of Denmark, Roskilde, Denmark

Abstract. For load calculations on wind turbines it is usually assumed that the turbulence approaching the rotor does not change its statistics as it goes through the induction zone. We investigate this assumption using a nacelle-mounted forward-looking pulsed lidar that measures low-frequency wind fluctuations simultaneously at distances between 0.5 and 3 rotor diameters upstream. The measurements show that below rated wind speed the low-frequency wind variance is reduced by up to 10% at 0.5 rotor diameters upstream and above rated enhanced by up to 20%. A quasi-steady model that takes into account the change in thrust coefficient with wind speed explains these variations partly. Large eddy simulations of turbulence approaching an actuator disk model of a rotor support the finding that the slope of the thrust curve influences the low-frequency fluctuations.

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Turbulence is usually assumed to be unmodified by the stagnation occurring in front of a wind turbine rotor. All manufacturers assume this in their dynamic load calculations. If this assumption is not true it might bias the load calculations and the turbines might not be designed optimally. We investigate the assumption with a Doppler lidar measuring forward from the top of the nacelle and find small but systematic changes in the approaching turbulence that depend on the power curve.
Turbulence is usually assumed to be unmodified by the stagnation occurring in front of a wind...