Boundary-Layer Meteorology

, Volume 156, Issue 3, pp 395–413 | Cite as

A Wind-Tunnel Simulation of the Wake of a Large Wind Turbine in a Weakly Unstable Boundary Layer

  • P. E. HancockEmail author
  • S. Zhang


Measurements have been made in the wake of a model wind turbine in both a weakly unstable and a baseline neutral atmospheric boundary layer, in the EnFlo stratified-flow wind tunnel, between 0.5 and 10 rotor diameters from the turbine, as part of an investigation of wakes in offshore winds. In the unstable case the velocity deficit decreases more rapidly than in the neutral case, largely because the boundary-layer turbulence levels are higher with consequent increased mixing. The height and width increase more rapidly in the unstable case, though still in a linear manner. The vertical heat flux decreases rapidly through the turbine, recovering to the undisturbed level first in the lower part of the wake, and later in the upper part, through the growth of an internal layer. At 10 rotor diameters from the turbine, the wake has strong features associated with the surrounding atmospheric boundary layer. A distinction is drawn between direct effects of stratification, as necessarily arising from buoyant production, and indirect effects, which arise only because the mean shear and turbulence levels are altered. Some aspects of the wake follow a similarity-like behaviour. Sufficiently far downstream, the decay of the velocity deficit follows a power law in the unstable case as well as the neutral case, but does so after a shorter distance from the turbine. Tentatively, this distance is also shorter for a higher loading on the turbine, while the power law itself is unaffected by turbine loading.


Atmospheric boundary layer Unstable boundary layer  Wind-tunnel experiment Wind-turbine wakes 



The work reported here was done under the SUPERGEN programme of the Engineering and Physical Sciences Research Council, SUPERGEN-Wind Phase 2, reference EP/H018662/1. Further details can be found from The authors are particularly grateful to Dr. P. Hayden, for assistance in setting up the experiments, and to Prof. A. G. Robins, for useful discussions and comment during the programme of research. The EnFlo wind tunnel is a NERC/NCAS national facility, and the authors are also grateful to NCAS for the support provided.


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Copyright information

© Springer Science+Business Media Dordrecht 2015

Authors and Affiliations

  1. 1.EnFlo Laboratory, Faculty of Engineering and Physical SciencesUniversity of SurreyGuildfordUK
  2. 2.School of Mechanical, Aerospace and Civil EngineeringUniversity of ManchesterManchesterUK

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