Volume 3, issue 1 | Copyright
Wind Energ. Sci., 3, 329-343, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research articles 01 Jun 2018

Research articles | 01 Jun 2018

Wind tunnel experiments on wind turbine wakes in yaw: effects of inflow turbulence and shear

Jan Bartl1, Franz Mühle2, Jannik Schottler3, Lars Sætran1, Joachim Peinke3,4, Muyiwa Adaramola2, and Michael Hölling3 Jan Bartl et al.
  • 1Department of Energy and Process Engineering, Norwegian University of Science and Technology, Trondheim, Norway
  • 2Faculty of Environmental Sciences and Natural Resource Management, Norwegian University of Life Sciences, Ås, Norway
  • 3ForWind, Institute of Physics, University of Oldenburg, Oldenburg, Germany
  • 4Fraunhofer IWES, Oldenburg, Germany

Abstract. The wake characteristics behind a yawed model wind turbine exposed to different customized inflow conditions are investigated. Laser Doppler anemometry is used to measure the wake flow in two planes at xD = 3 and xD = 6, while the turbine yaw angle is varied from γ = −30° to 0° to +30°. The objective is to assess the influence of grid-generated inflow turbulence and shear on the mean and turbulent flow components.

The wake flow is observed to be asymmetric with respect to negative and positive yaw angles. A counter-rotating vortex pair is detected creating a kidney-shaped velocity deficit for all inflow conditions. Exposing the rotor to non-uniform highly turbulent shear inflow changes the mean and turbulent wake characteristics only insignificantly. At low inflow turbulence the curled wake shape and wake center deflection are more pronounced than at high inflow turbulence. For a yawed turbine the rotor-generated turbulence profiles peak in regions of strong mean velocity gradients, while the levels of peak turbulence decrease at approximately the same rate as the rotor thrust.

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Short summary
Wake steering by yawing a wind turbine offers great potential to increase the wind farm power production. A model scale experiment in a controlled wind tunnel environment has been performed to map the wake flow's complex velocity distribution for different inflow conditions. A non-uniform sheared inflow was observed to affect the wake flow only insignificantly. The level of turbulent velocity fluctuations in the inflow, however, influenced the wake's velocity distribution to a higher degree.
Wake steering by yawing a wind turbine offers great potential to increase the wind farm power...