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Wind Energy Science The interactive open-access journal of the European Academy of Wind Energy
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https://doi.org/10.5194/wes-2018-69
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/wes-2018-69
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research articles 27 Nov 2018

Research articles | 27 Nov 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Wind Energy Science (WES).

Qualitative yaw stability analysis of free-yawing downwind turbines

Gesine Wanke1, Morten H. Hansen2, and Torben J. Larsen3 Gesine Wanke et al.
  • 1Suzlon Blade Science Center, Havneparken 1, 7100 Vejle, Denmark
  • 2Mads Clausen Institute, University of Southern Denmark, Alison 2, 6400 Sønderborg, Denmark
  • 3DTU Wind Energy, Technical University of Denmark, Frederiksborgvej 399, 4000 Roskilde, Denmark

Abstract. This article shows qualitatively the yaw stability of a free yawing downwind turbine and the ability of the turbine to align passively with the wind direction, using a two degree of freedom model. An existing model of a Suzlon S111 upwind 2.1MW turbine is converted into a downwind configuration with a 5° tilt and a 3.5° downwind cone angle. The analysis shows that the static tilt angle causes a wind speed dependent yaw misalignment of up to −19° due to the projection of the torque onto the yaw bearing and the skewed aerodynamic forces caused by wind speed projection. With increased cone angles, the yaw stiffness can be increased for better yaw alignment and the stabilization of the free yaw motion. The shaft length influences the yaw alignment only for high wind speeds and cannot significantly contribute to the damping of the free yaw mode within the investigated range. Asymmetric flapwise blade flexibility is seen to significantly decrease the damping of the free yaw mode, leading to instability at wind speeds higher than 19ms−1. It is shown that this additional degree of freedom is needed to predict the qualitative yaw behaviour of a free yawing downwind wind turbine.

Gesine Wanke et al.
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In this paper the results of the stability analysis of a free yawing downwind turbine is shown and the turbines ability to align the rotor passively with the wind direction is investigated. The results show that a tilt angle causes the equilibrium yaw position of free yawing downwind to be non-zero. It is shown that an increase in cone angle can stabilize the free yaw mode significantly, while blade flapwise flexibility will increase the risk of a instability of the free yaw mode.
In this paper the results of the stability analysis of a free yawing downwind turbine is shown...
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