Journal cover Journal topic
Wind Energy Science The interactive open-access journal of the European Academy of Wind Energy
https://doi.org/10.5194/wes-2017-22
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research articles
30 Jun 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Wind Energy Science (WES).
Impacts of the Low-Level Jet's Negative Wind Shear on the Wind Turbine
Walter Gutierrez1,2, Arquimedes Ruiz-Columbie2, Murat Tutkun3,4, and Luciano Castillo1 1Department of Mechanical Engineering, Texas Tech University, Lubbock, Texas 79409, USA
2National Wind Institute, Texas Tech University, Lubbock, Texas 79409, USA
3Institute for Energy Technology (IFE), Kjeller, Norway
4University of Oslo, Department of Mathematics, Oslo, Norway
Abstract. Nocturnal Low Level Jets (LLJs) are defined as relative maxima in the vertical profile of the horizontal wind speed at the top of the stable boundary layer. Such peaks constitute major power resources for wind turbines. However, a wind speed maximum implies a transition from positive wind shears below the peak to negative ones above. The effect that such transition inflicts on wind turbines has not been thoroughly studied. High-frequency data of actual atmospheric LLJs were used as input to the NREL aeroelastic simulator FAST code, and simulations were performed with different vertical distances between the LLJ peak and the wind turbine hub. It was found that the presence of negative wind shears at the heights of the turbine appeared to exert a positive impact in reducing the motions of the nacelle and the tower in every direction, with oscillations reaching a minimum when negative shears covered completely the turbine sweeping area. Only the tower wobbling in the spanwise direction was amplified by the negative shears; however, this occurred at slower velocities and accelerations. The forces and moments were also reduced by the negative shears. The aforementioned impacts were less beneficial in the rotating parts such as the blades and the shafts. Finally, the power output was slightly more stable. Those findings can be very important for the next generation of wind turbines as they reach deeper into the heights of more LLJs.

Citation: Gutierrez, W., Ruiz-Columbie, A., Tutkun, M., and Castillo, L.: Impacts of the Low-Level Jet's Negative Wind Shear on the Wind Turbine, Wind Energ. Sci. Discuss., https://doi.org/10.5194/wes-2017-22, in review, 2017.
Walter Gutierrez et al.
Walter Gutierrez et al.
Walter Gutierrez et al.

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Short summary
Low-level jets (LLJ) are fast flows in the low atmosphere, usually seen at night, with a wind speed peak between 100–1000 m above the ground. More wind energy can be captured if a LLJ is present. The positive wind shear below the peak augment the damages on wind turbines. However, our results show that the negative shears above actually decrease the mechanical loading. Therefore, reaching negative shears more often reduce the LLJs' adverse impacts and make more feasible to harness their power.
Low-level jets (LLJ) are fast flows in the low atmosphere, usually seen at night, with a wind...
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