Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Wind-turbine wake flows - Effects of boundary layers and periodic disturbances
KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The increased fatigue loads and decreased power output of a wind turbine placed in the wake of another turbine is a well-known problem when building new wind-power farms and a subject of intensive research. These problems are caused by the velocity gradients and high turbulence levels present in the wake of a turbine. In order to better estimate the total power output and life time of a wind-power farm, knowledge about the development and stability of wind-turbine wakes is crucial.

In the present thesis, the flow field around small-scale model wind turbines has been investigated experimentally in two wind tunnels. The flow velocity was measured with both hot-wire anemometry and particle image velocimetry. To monitor the turbine performance, the rotational frequency, the power output and the total drag force on the turbine were also measured. The power and thrust coefficients for different tip-speed ratios were calculated and compared to the blade element momentum method, with a reasonable agreement. The same method was also used to design and manufacture new turbine blades, which gave an estimate of the distribution of the lift and drag forces along the blades.

The influence of the inlet conditions on the turbine and the wake properties was studied by subjecting the turbine to both uniform in flow and different types of boundary layer in flows. In order to study the stability and development of the tip vortices shed from the turbine blades, a new experimental setup for phase-locked measurements was constructed. The setup made it possible to introduce perturbations of different frequencies and amplitudes, located in the rear part of the nacelle. With a newly developed method, it was possible to characterize the vortices and follow their development downstream, using only the streamwise velocity component.

Measurements were also performed on porous discs placed in different configurations. The results highlighted the importance of turbine spacings. Both the measurements on the turbine and the discs were also used to compare with large eddy simulations using the actuator disc method. The simulations managed to predict the mean velocity fairly well in both cases, while larger discrepancies were seen in the turbulence intensity.

 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. , viii, 35 p.
Series
TRITA-MEK, ISSN 0348-467X ; 2014:12
Keyword [en]
wind power, wind-turbine model, wind tunnel, porous disc, hot-wire anemometry, particle image velocimetry, blade element momentum method, large eddy simulations, actuator disc method
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-144475ISBN: 978-91-7595-112-6 (print)OAI: oai:DiVA.org:kth-144475DiVA: diva2:713584
Public defence
2014-05-14, D2, Lindstedtsvägen 5, KTH, Stockholm, 10:15 (English)
Opponent
Supervisors
Funder
Swedish Energy Agency
Note

QC 20140424

Available from: 2014-04-24 Created: 2014-04-23 Last updated: 2014-04-24Bibliographically approved
List of papers
1. Phase-locked hot-wire measurements on the breakdown of wind turbine tip vortices
Open this publication in new window or tab >>Phase-locked hot-wire measurements on the breakdown of wind turbine tip vortices
(English)Manuscript (preprint) (Other academic)
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-94012 (URN)
Note

QS 2012

Available from: 2012-05-04 Created: 2012-05-04 Last updated: 2014-04-24Bibliographically approved
2. The stability and development of tip and root vortices behind a model wind turbine
Open this publication in new window or tab >>The stability and development of tip and root vortices behind a model wind turbine
2013 (English)In: Experiments in Fluids, ISSN 0723-4864, E-ISSN 1432-1114, Vol. 54, no 9, 1591- p.Article in journal (Refereed) Published
Abstract [en]

When designing new wind farms, one has to rely on models describing the flow field around and inside the farm, since direct numerical simulation is far too computationally expensive. In order to develop better models for power prediction of wind farms, knowledge about the flow field around turbines, the stability of the wakes and the interaction between them is essential. Since the conditions during field measurements are difficult to control, wind tunnel measurements play an important role when studying wakes behind wind turbines. Within the present work, an experimental methodology has been developed to study the evolution and stability of the tip vortices shed from the rotor blades of a small-scale turbine model. The stability of the tip vortices was studied by introducing a periodic disturbance to the flow, which is shown to have a clear effect on the development of the vortices. Prior to the vortex breakdown, clear signs of vortex pairing were also observed. A parameter study was performed by varying the amplitude and frequency of the forced disturbance, and the effect on the tip vortices was evaluated. This experiment is one of the first where the influence of a periodic disturbance on a wind turbine wake is studied, something that previously has been performed in a number of numerical studies.

Keyword
Horizontal-Axis, Boundary-Layer, Wake
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-133974 (URN)10.1007/s00348-013-1591-6 (DOI)000326043500006 ()2-s2.0-84882495356 (Scopus ID)
Funder
Swedish Energy Agency
Note

QC 20131115

Available from: 2013-11-15 Created: 2013-11-14 Last updated: 2017-12-06Bibliographically approved
3. Effects of the inflow conditions on the performance and near wake structure of a model wind turbine
Open this publication in new window or tab >>Effects of the inflow conditions on the performance and near wake structure of a model wind turbine
(English)Manuscript (preprint) (Other academic)
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-144514 (URN)
Note

QS 2014

Available from: 2014-04-24 Created: 2014-04-24 Last updated: 2014-04-24Bibliographically approved
4. The effects of a model forest canopy on the outputs of a wind turbine model
Open this publication in new window or tab >>The effects of a model forest canopy on the outputs of a wind turbine model
2014 (English)In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 555, no 1, 012079Article in journal (Refereed) Published
Abstract [en]

The effects of a rough surface boundary layer on the outputs of a wind turbine model were investigated experimentally in a wind tunnel. The very rough surface consisted of cylindrical pins, in order to model a forest canopy. The hub height of the turbine model was varied in order to see the effect of the presence of the model forest in the power and thrust coefficients. A small effect of the hub height was observed in the averaged power coefficient, where the turbine produced less for the lowest hub height. The difference was however reduced when scaling the power output with the available power in the wind instead of using the velocity at hub height. Consistent trends were present in the standard deviation of the thrust coefficient and the rotational speed, which both increased by decreasing the hub height. This underlines the fact that not only the rotor but also the tower and the bearings of a wind turbine must withstand to increased loads when operating close to a canopy.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2014
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-144515 (URN)10.1088/1742-6596/555/1/012079 (DOI)000347871200079 ()2-s2.0-84919483526 (Scopus ID)
Conference
4th Scientific Conference on the Science of Making Torque from Wind; Oldenburg, Germany, 9 October-11 October 2012
Funder
StandUp for Wind
Note

Updated from manuscript to article in journal.

QC 20150213

Available from: 2014-04-24 Created: 2014-04-24 Last updated: 2017-12-05Bibliographically approved
5. Wind tunnel experiments on small-scale model wind turbines: A comparative study using different airfoils
Open this publication in new window or tab >>Wind tunnel experiments on small-scale model wind turbines: A comparative study using different airfoils
(English)Manuscript (preprint) (Other academic)
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-144516 (URN)
Note

QS 2014

Available from: 2014-04-24 Created: 2014-04-24 Last updated: 2014-04-24Bibliographically approved
6. On the wake flow interaction between two perforated discs with varying mutual distance
Open this publication in new window or tab >>On the wake flow interaction between two perforated discs with varying mutual distance
(English)Manuscript (preprint) (Other academic)
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-144517 (URN)
Note

QS 2014

Available from: 2014-04-24 Created: 2014-04-24 Last updated: 2014-04-24Bibliographically approved
7. Large eddy simulations of the wake flow behind a model wind turbine and porous discs
Open this publication in new window or tab >>Large eddy simulations of the wake flow behind a model wind turbine and porous discs
(English)Manuscript (preprint) (Other academic)
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-144518 (URN)
Note

QS 2014

Available from: 2014-04-24 Created: 2014-04-24 Last updated: 2014-04-24Bibliographically approved
8. The design of turbine blades for a small-scale model wind turbine using the BEM method
Open this publication in new window or tab >>The design of turbine blades for a small-scale model wind turbine using the BEM method
(English)Manuscript (preprint) (Other academic)
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-144519 (URN)
Note

QS 2014

Available from: 2014-04-24 Created: 2014-04-24 Last updated: 2014-04-24Bibliographically approved

Open Access in DiVA

Thesis(25199 kB)705 downloads
File information
File name FULLTEXT02.pdfFile size 25199 kBChecksum SHA-512
e5b8630bf100ec1640e871abfc67332f074c06cd6f6328a4f8a10dcec258b9f933eb878e628ad4ecd4a58dde629f5c906078309049dc5d746fd0b93514b34e94
Type fulltextMimetype application/pdf

Search in DiVA

By author/editor
Odemark, Ylva
By organisation
Fluid PhysicsLinné Flow Center, FLOW
Fluid Mechanics and Acoustics

Search outside of DiVA

GoogleGoogle Scholar
Total: 705 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 609 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf