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Wind Energy Science The interactive open-access journal of the European Academy of Wind Energy
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Discussion papers
https://doi.org/10.5194/wes-2019-31
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/wes-2019-31
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research articles 27 Jun 2019

Research articles | 27 Jun 2019

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

Effect of tip spacing, thrust coefficient and turbine spacing inmulti-rotor wind turbines and farms

Niranjan S. Ghaisas1, Aditya S. Ghate2, and Sanjiva K. Lele1,2,3 Niranjan S. Ghaisas et al.
  • 1Center for Turbulence Research, Stanford University, Stanford, CA 94305, USA
  • 2Department of Aeronautics and Astronautics, Stanford University, Stanford, CA 94305, USA
  • 3Department of Mechanical Engineering, Stanford University, Stanford, CA 94305, USA

Abstract. Large eddy simulations (LES) are performed to study the wakes of a multi-rotor wind turbine configuration comprising of four identical rotors mounted on a single tower. The multi-rotor turbine wakes are compared to the wake of a conventional turbine comprising of a single rotor per tower with the same frontal area, hub height and thrust coefficient. The multi-rotor turbine wakes are found to recover faster, while the turbulence intensity in the wake is smaller, compared to the wake of the conventional turbine. The differences with the wake of a conventional turbine increase as the spacing between the tips of the rotors in the multi-rotor configuration increases. The differences are also sensitive to the thrust coefficients used for all rotors, with more pronounced differences for larger thrust coefficients. The interaction between multiple multi-rotor turbines is contrasted with that between multiple single-rotor turbines by considering wind farms with five turbine units aligned perfectly with each other and with the wind direction. Similar to the isolated turbine results, multi-rotor wind farms show smaller wake losses and smaller turbulence intensity compared to wind farms comprised of conventional single-rotor turbines. The benefits of multi-rotor wind farms over single-rotor wind farms increase with increasing tip spacing, irrespective of the axial spacing and thrust coefficient. The mean velocity profiles and relative powers of turbines obtained from the LES results are predicted reasonably accurately by an analytical model assuming Gaussian radial profiles of the velocity deficits and a hybrid linear-quadratic model for merging of wakes. These results show that a larger planform energy flux can be achieved without significantly increased fatigue loads by using multi-rotor turbines instead of conventional, single-rotor turbines.

Niranjan S. Ghaisas et al.
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Niranjan S. Ghaisas et al.
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Latest update: 23 Jul 2019
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Short summary
Wakes of a novel multi-rotor wind turbine configuration are evaluated using numerical simulations. Compared to equivalent conventional single-rotor turbine wakes, multi-rotor turbine wakes are found to recover faster and generate lesser turbulence. Consequently, multi-rotor turbine wind farms are more efficient, with smaller wake losses. The benefits of multi-rotor wind farms over conventional wind farms are sensitive to tip spacing, thrust coefficient and turbine spacing.
Wakes of a novel multi-rotor wind turbine configuration are evaluated using numerical...
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