Impact of freestream turbulence and thrust coefficient on wind turbine-generated wakes
Author(s)
Bourhis, Martin
Messmer, Thomas
Hölling, Michael
Buxton, Oliver
Type
Journal Article
Abstract
This study investigates the influence of free-stream turbulence (FST) and the thrust coefficient (CT) on wind turbine wakes. Wakes generated at CT ∈{0.5,0.7,0.9} are
exposed to turbulent inflows with varying FST intensities (1 % ≲ TI∞ ≲11%)andintegral length scales (0.1 ≲ Lx/D ≲2, D is the rotor diameter). For high-TI∞ inflows, a flow
region in the wake is observed where a mean momentum deficit persists despite the turbulence intensity having already homogenised with that of the free stream, challenging traditional wake definitions. A ‘turning point’ in the mean wake width evolution is identified, beyond which wakes spread at slower rates. Near-field (x/D ≲7) wake growth rate increases with higher TI∞ and CT, while far-field (x/D ≳15) wake growth rate decreases with higher TI∞– a finding with profound implications for wind turbine wake modelling that also aligns with the entrainment behaviours observed in bluff- and porous
body wakes exposed to FST. Increasing Lx delays wake recovery onset and reduces the mean wake width, with minimal effect on the spreading rate. Both CT and FST influence the high- and low-frequency wake dynamics, with varying contributions in the near and far fields. For low-TI∞ and small-Lx inflows, wake meandering is minimal, sensitive to CT and appears to be triggered by a shear-layer instability. Wake meandering is enhanced
for high-TI∞ and large-Lx inflows, with the integral length scale playing a leading role. This emphasises the complex role of FST integral length scale: while increasing Lx amplifies meandering, it does not necessarily translate to larger mean wake width due
to the concurrent suppression of entrainment rate.
exposed to turbulent inflows with varying FST intensities (1 % ≲ TI∞ ≲11%)andintegral length scales (0.1 ≲ Lx/D ≲2, D is the rotor diameter). For high-TI∞ inflows, a flow
region in the wake is observed where a mean momentum deficit persists despite the turbulence intensity having already homogenised with that of the free stream, challenging traditional wake definitions. A ‘turning point’ in the mean wake width evolution is identified, beyond which wakes spread at slower rates. Near-field (x/D ≲7) wake growth rate increases with higher TI∞ and CT, while far-field (x/D ≳15) wake growth rate decreases with higher TI∞– a finding with profound implications for wind turbine wake modelling that also aligns with the entrainment behaviours observed in bluff- and porous
body wakes exposed to FST. Increasing Lx delays wake recovery onset and reduces the mean wake width, with minimal effect on the spreading rate. Both CT and FST influence the high- and low-frequency wake dynamics, with varying contributions in the near and far fields. For low-TI∞ and small-Lx inflows, wake meandering is minimal, sensitive to CT and appears to be triggered by a shear-layer instability. Wake meandering is enhanced
for high-TI∞ and large-Lx inflows, with the integral length scale playing a leading role. This emphasises the complex role of FST integral length scale: while increasing Lx amplifies meandering, it does not necessarily translate to larger mean wake width due
to the concurrent suppression of entrainment rate.
Date Issued
2025-11-25
Date Acceptance
2025-10-01
Citation
Journal of Fluid Mechanics, 2025, 1023
ISSN
0022-1120
Publisher
Cambridge University Press
Journal / Book Title
Journal of Fluid Mechanics
Volume
1023
Copyright Statement
©TheAuthor(s), 2025. Published by Cambridge University Press.This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (https://creativecommons.org/ licenses/by/4.0/), which permits unrestricted re-use, distribution and reproduction, provided the original article is properly cited.
License URL
Publication Status
Published
Article Number
A3
Date Publish Online
2025-11-10