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
Large-eddy simulations of the Lillgrund wind farm
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. Uppsala University Campus Gotland, Sweden.
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. Uppsala University Campus Gotland, Sweden.
Show others and affiliations
2015 (English)In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 18, no 3, 449-467 p.Article in journal (Refereed) Published
Abstract [en]

The power production of the Lillgrund wind farm is determined numerically using large-eddy simulations and compared with measurements. In order to simulate realistic atmospheric conditions, pre-generated turbulence and wind shear are imposed in the computational domain. The atmospheric conditions are determined from data extracted from a met mast, which was erected prior to the establishment of the farm. In order to allocate most of the computational power to the simulations of the wake flow, the turbines are modeled using an actuator disc method where the discs are imposed in the computational domain as body forces which for every time step are calculated from tabulated airfoil data. A study of the influence of imposed upstream ambient turbulence is performed and shows that higher levels of turbulence results in slightly increased total power production and that it is of great importance to include ambient turbulence in the simulations. By introducing ambient atmospheric turbulence, the simulations compare very well with measurements at the studied inflow angles. A final study aiming at increasing the farm production by curtailing the power output of the front row turbines and thus letting more kinetic energy pass downstream is performed. The results, however, show that manipulating only the front row turbines has no positive effect on the farm production, and therefore, more complex curtailment strategies are needed to be tested.

Place, publisher, year, edition, pages
John Wiley & Sons, 2015. Vol. 18, no 3, 449-467 p.
Keyword [en]
Actuator disc, Large-eddy simulation, Power estimation, Wakes, Wind farms
National Category
Energy Engineering
Identifiers
URN: urn:nbn:se:kth:diva-109519DOI: 10.1002/we.1707ISI: 000348899700005Scopus ID: 2-s2.0-84921862637OAI: oai:DiVA.org:kth-109519DiVA: diva2:583065
Note

QC 20150318. Updated from submitted to published.

Available from: 2013-01-07 Created: 2013-01-07 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Numerical computations of wind turbine wakes and wake interaction: Optimization and control
Open this publication in new window or tab >>Numerical computations of wind turbine wakes and wake interaction: Optimization and control
2012 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In the present thesis the wake flow behind wind turbines is analyzed numerically using large-eddy simulations. The wind turbine rotors are modeled by using either the actuator disc method or the actuator line method in which the blades are represented by body forces computed with airfoil data. Using these models, the boundary layers of the turbine blades are not resolved and most of the computational power is preserved to simulate the wake flow. The actuator disc method is used for the wake interaction studies of the Lillgrund wind farm. In this study the power production is simulated for two different wind directions and compared to measurements. A grid sensitivity study and a turbulence intensity study are also performed. As a last step the front row turbines are derated in an attempt to increase the total production of the farm. The results show that it is important to impose atmospheric conditions at the inlet in the simulations, otherwise production will be unrealistically low for some turbines in the farm. The agreement between the simulated and measured power is very good. The study based on derating the front row turbines does not show any positive increase on the farm production. The actuator line method is used for near wake analysis of the MEXICO rotor. In this study the near wake is simulated for five different flow cases and compared with particle image velocimetry (PIV) measurements. The analysis is performed by comparing size and circulation of the tip vortices, the radial and streamwise velocity distributions, the spatial expansion of the wake and the axial induction factor. The simulations and measurements generally are in agreement. In some cases, however, the measurements are affected by tunnel effects which are not captured in the simulations. In connection to the actuator disc method a power control strategy for operating conditions below rated power is implemented and tested. The strategy is first validated using an in-house developed blade element momentum code and then is implemented in the actuator disc method used in the EllipSys3D code. The initial tests show that the strategy responds as expected when changing the moment of inertia of the rotor and when varying the inlet conditions. Results from the implementation of the strategy in the actuator disc method in EllipSys3D show that the turbine adapts to the conditions it is operating in by changing its rotational velocity and power output when the inlet conditions are varied.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. vi, 56 p.
Series
Trita-MEK, ISSN 0348-467X ; 2012:18
Keyword
Actuator disc method, Actuator line method, Blade element momentum method, Wind turbine wake, Wake interaction, CFD, LES, EllipSys3D
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-109522 (URN)978-91-7501-624-5 (ISBN)
Presentation
2013-01-25, D33, Lindstedtsvägen 5, KTH, Stockholm, 10:15 (English)
Opponent
Supervisors
Note

QC 20130111

Available from: 2013-01-11 Created: 2013-01-07 Last updated: 2013-01-11Bibliographically approved
2. Numerical computations of wind turbine wakes and wake interaction
Open this publication in new window or tab >>Numerical computations of wind turbine wakes and wake interaction
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

When wind turbines are placed in farms, wake effects reduce the overall power production. Also, turbine loads are significantly increased since turbulence levels are high within the wake flow. Therefore, when planning for a wind farm, it is imperative to have an understanding of the flow conditions in the farm in order to estimate the power losses and to optimize the durability of the turbines to be selected for the farm. The possibilities granted by numerical modeling and the development of computational capabilities give an opportunity to study these flow conditions in detail, which has been the key focus of this doctoral work.

The actuator disc method is used for predicting the power production of the Lillgrund wind farm. The results of the simulations are compared to measurements from the actual wind farm, which are found to be in very good agreement. However, some uncertainties are identified in the modeling of the turbine. One of the uncertainties is that a generic rotor is used in the Lillgrund case. In order to quantify the errors resulting from this generalization three different rotor configurations are simulated in various flow conditions. Generally, it can be stated that the choice of rotor configuration is not crucial if the intention of the simulations is to compute the mean wake characteristics subject to turbulent inflow. Another uncertainty is that the turbines in the Lillgrund case were simulated without a power controller. Therefore, a power controller is implemented and used in simulations. Generally, the controller reduces the thrust of the turbines, reduces turbulence intensity and increases velocity levels in the wake flow. However, the use of a controller was observed to have a small impact on the power production.

The effects of using the technique of imposing pregenerated turbulence and a prescribed boundary layer in the simulation are analyzed in order to verify its applicability in very long domains. It is observed that close to the plane of imposed turbulence, the conditions are mainly dependent on the imposed turbulence while far downstream the turbulence, regardless of its initial characteristics, is in near equilibrium with the prescribed wind shear.

The actuator line method is validated using measurements of the near wake behind the MEXICO rotor. The analysis is performed by comparing position, size and circulation of the tip vortices, as well as velocity distributions in the wake flow. The simulations and measurements are generally found to be in good agreement apart from the tip vortex size, which is greatly overestimated in the simulations.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. ix, 40 p.
Series
TRITA-MEK, ISSN 0348-467X ; 2015:04
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-166658 (URN)978-91-7595-558-2 (ISBN)
Public defence
2015-06-04, Sal F3, Lindstedtsvägen 26, KTH, Stockholm, 10:15 (English)
Opponent
Supervisors
Note

QC 20150519

Available from: 2015-05-19 Created: 2015-05-13 Last updated: 2015-05-19Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full textScopus

Authority records BETA

Henningson, Dan

Search in DiVA

By author/editor
Nilsson, KarlIvanell, StefanHenningson, Dan
By organisation
MechanicsLinné Flow Center, FLOW
In the same journal
Wind Energy
Energy Engineering

Search outside of DiVA

GoogleGoogle Scholar

doi
urn-nbn

Altmetric score

doi
urn-nbn
Total: 211 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