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
Phase-locked hot-wire measurements on the breakdown of wind turbine tip vortices
KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.ORCID iD: 0000-0002-3251-8328
(English)Manuscript (preprint) (Other academic)
National Category
Mechanical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-94012OAI: oai:DiVA.org:kth-94012DiVA: diva2:524994
Note

QS 2012

Available from: 2012-05-04 Created: 2012-05-04 Last updated: 2014-04-24Bibliographically approved
In thesis
1. Wakes behind wind turbines - Studies on tip vortex evolution and stability
Open this publication in new window or tab >>Wakes behind wind turbines - Studies on tip vortex evolution and stability
2012 (English)Licentiate 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. In order to better estimate the total power output of a wind power farm, knowledge about the development and stability of wind turbine wakes is crucial. In the present thesis, the wake behind a small-scale model turbine was investigated experimentally in a wind tunnel. The velocity in the wake was measured with hot-wire anemometry, for different free stream velocities and tip speed ratios. To characterize the behaviour of the model turbine, the power output, thrust force and rotational frequency of the model were also measured. These results were then compared to calculations using the Blade Element Momentum (BEM) method. New turbine blades for the model was constructed using the same method, in order to get an estimate of the distribution of the lift and drag forces along the blades. This information is needed for comparisons with certain numerical simulations, which however remains to be performed.By placing the turbine at different heights in a turbulent boundary layer, the effects of forest turbulence on wind turbine outputs (power and thrust) could also be investigated.The evolution of the tip vortices shed from the turbine blades was studied by performing velocity measurements around the location of the tip vortex breakdown. The vortices' receptivity to disturbances was then studied by introducing a disturbance in the form of two pulsed jets, located in the rear part of the nacelle. In order to introduce a well-defined disturbance and perform phase-locked measurements, a new experimental setup was constructed and successfully tested for two different disturbance frequencies. The mean streamwise velocity and the streamwise turbulence intensity was found to scale well with the free stream velocity and the spreading of the wake was found to be proportional to the square root of the downstream distance.  The comparison for power and thrust between measurements and BEM calculations showed good agreement in some cases but worse agreement when the pitch angle of the blades was small.The velocity measurements showed that the tip vortices can be susceptible to disturbances and an earlier breakdown could be detected. However, more measurements need to be made to fully investigate the dependance on disturbance frequency and amplitude.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. vi, 78 p.
Series
Trita-MEK, ISSN 0348-467X ; 2012:06
Keyword
wind power, aerodynamics, hot-wire anemometry, vortex dynamics
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-93806 (URN)
Presentation
2012-05-22, E33, Lindstedtsvägen 3, Stockholm, 10:15 (English)
Opponent
Supervisors
Note
QC 20120504Available from: 2012-05-04 Created: 2012-04-27 Last updated: 2012-05-04Bibliographically approved
2. Wind-turbine wake flows - Effects of boundary layers and periodic disturbances
Open this publication in new window or tab >>Wind-turbine wake flows - Effects of boundary layers and periodic disturbances
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
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:nbn:se:kth:diva-144475 (URN)978-91-7595-112-6 (ISBN)
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

Open Access in DiVA

No full text

Authority records BETA

Fransson, Jens

Search in DiVA

By author/editor
Odemark, YlvaFransson, Jens
By organisation
Fluid PhysicsLinné Flow Center, FLOW
Mechanical Engineering

Search outside of DiVA

GoogleGoogle Scholar

urn-nbn

Altmetric score

urn-nbn
Total: 107 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