Energy exchanges between coherent modes in the near wake of a wind turbine model at different tip speed ratios
Author(s)
Biswas, Neelakash
Buxton, Oliver
Type
Journal Article
Abstract
In this work we investigate the spatio-temporal nature of various coherent modes present in
a wind turbine wake using a combination of new particle image velocimetry experiments
and data from Biswas & Buxton (J. Fluid Mech., vol. 979, 2024, A34). A multiscale
triple decomposition of the acquired velocity field is sought to extract the coherent modes
and, thereafter, the energy exchanges to and from them are studied using the multiscale
triple decomposed coherent kinetic energy budgets developed by Baj & Buxton (Phys.
Rev. Fluids, vol. 2, 2017, 114607). Different frequencies forming the tip vortex system
(such as the blade passing frequency, turbine’s rotational frequency and their harmonics)
are found to be energised by different sources such as production from the mean flow
or nonlinear triadic interaction or both, similar to the primary, secondary or the mixed
modes discussed in Biswas et al. (J. Fluid Mech., vol. 941, 2022, A36). The tip vortex
system forms a complex network of nonlinear triadic energy transfers, the nature and
the magnitudes of which depend on the tip speed ratio (λ). Contrastingly, the modes
associated with the sheddings from the nacelle or tower and wake meandering are found
to be primarily energised by the mean flow. We show that the tip vortex system exchanges
energy with the mean flow primarily through the turbine’s rotational frequency. In fact, the
system transfers energy back to the mean flow through the turbine’s rotational frequency
at some distance downstream marking the onset location of wake recovery (xwr). Here xwr
is shown to reduce with λ due to stronger interaction and earlier merging of the tip vortices
at a higher λ.
a wind turbine wake using a combination of new particle image velocimetry experiments
and data from Biswas & Buxton (J. Fluid Mech., vol. 979, 2024, A34). A multiscale
triple decomposition of the acquired velocity field is sought to extract the coherent modes
and, thereafter, the energy exchanges to and from them are studied using the multiscale
triple decomposed coherent kinetic energy budgets developed by Baj & Buxton (Phys.
Rev. Fluids, vol. 2, 2017, 114607). Different frequencies forming the tip vortex system
(such as the blade passing frequency, turbine’s rotational frequency and their harmonics)
are found to be energised by different sources such as production from the mean flow
or nonlinear triadic interaction or both, similar to the primary, secondary or the mixed
modes discussed in Biswas et al. (J. Fluid Mech., vol. 941, 2022, A36). The tip vortex
system forms a complex network of nonlinear triadic energy transfers, the nature and
the magnitudes of which depend on the tip speed ratio (λ). Contrastingly, the modes
associated with the sheddings from the nacelle or tower and wake meandering are found
to be primarily energised by the mean flow. We show that the tip vortex system exchanges
energy with the mean flow primarily through the turbine’s rotational frequency. In fact, the
system transfers energy back to the mean flow through the turbine’s rotational frequency
at some distance downstream marking the onset location of wake recovery (xwr). Here xwr
is shown to reduce with λ due to stronger interaction and earlier merging of the tip vortices
at a higher λ.
Date Issued
2024-10-10
Date Acceptance
2024-06-18
Citation
Journal of Fluid Mechanics, 2024, 996
ISSN
0022-1120
Publisher
Cambridge University Press
Journal / Book Title
Journal of Fluid Mechanics
Volume
996
Copyright Statement
© The Author(s), 2024. Published by Cambridge University Press. This is an Open Access article,
distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/
licenses/by/4.0), which permits unrestricted re-use, distribution and reproduction, provided the original
article is properly cited.
distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/
licenses/by/4.0), which permits unrestricted re-use, distribution and reproduction, provided the original
article is properly cited.
License URL
Identifier
https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/energy-exchanges-between-coherent-modes-in-the-near-wake-of-a-wind-turbine-model-at-different-tip-speed-ratios/B3291C715E28A05918F9EB4B3DB5511D
Publication Status
Published
Article Number
A8
Date Publish Online
2024-09-26