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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-2020-106
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/wes-2020-106
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  12 Oct 2020

12 Oct 2020

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This preprint is currently under review for the journal WES.

Evaluation of tilt control for wind-turbine arrays in the atmospheric boundary layer

Carlo Cossu Carlo Cossu
  • Laboratoire d’Hydrodynamique Énergetique et Environnement Atmosphèrique (LHEEA) CNRS - Centrale Nantes, 1 rue de la Noë 44300 Nantes, France

Abstract. Wake redirection is a promising approach designed to mitigate turbine-wake interactions which have a negative impact on the performance and lifetime of wind farms. It has recently been found that substantial power gains can be obtained by tilting the rotors of spanwise-periodic wind-turbine arrays. Rotor tilt is associated to the generation of coherent streamwise vortices which deflect wakes towards the ground and, by exploiting the vertical wind shear, replace them with higher-momentum fluid (high-speed streaks). The objective of this work is to evaluate power gains that can be obtained by tilting rotors in spanwise-periodic wind-turbine arrays immersed in the atmospheric boundary layer and, in particular, to analyze the influence of the rotor size on power gains in the case where the turbines emerge from the atmospheric surface layer. We show that, for the case of wind-aligned arrays, large power gains can be obtained for positive tilt angles of the order of 30°. Power gains are substantially enhanced by operating tilted-rotor turbines at thrust coefficients higher than in the reference configuration. These power gains initially increase with the rotor size reaching a maximum for rotor diameters of the order of five boundary layer momentum thicknesses (for the considered cases) and decrease for larger sizes. Maximum power gains are obtained for wind-turbine spanwise spacings which are very similar to those of large-scale and very large scale streaky motions which are naturally amplified in turbulent boundary layers. These results are all congruent with the findings of previous investigations of passive control of canonical boundary layers for drag-reduction applications where high-speed streaks replaced wakes of spanwise-periodic rows of wall-mounted roughness elements.

Carlo Cossu

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Latest update: 29 Oct 2020
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Short summary
We deal with wake redirection, which is a promising approach designed to mitigate turbine-wake interactions which have a negative impact on the performance and lifetime of wind farms. We show that substantial power gains can be obtained by tilting the rotors of spanwise-periodic wind-turbine arrays in the atmospheric boundary layer (ABL). An optimal rotor size exists which maximizes the global power extracted from the wind.
We deal with wake redirection, which is a promising approach designed to mitigate turbine-wake...
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