uu.seUppsala University Publications
Change search
ReferencesLink to record
Permanent link

Direct link
Wake downstream of the Lillgrund wind farm - A Comparison between LES using the actuator disc method and a Wind farm Parametrization in WRF
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
2015 (English)In: WAKE CONFERENCE 2015, 2015, 012028- p., 012028Conference paper (Refereed)
Abstract [en]

Simulations of the Lillgrund wind farm (located between Malmo and Copenhagen) are performed using both Large Eddy Simulation (LES) and mesoscale simulations in WRF. The aim is to obtain a better understanding of wakes generated by entire wind farms in order to improve the understanding of farm to farm interactions. The study compares the results from the two used models for the energy production and the wake characteristics downstream of the wind farm. A comparison is also performed with regards to the production data from the Lillgrund wind farm which has been filtered to be comparable to the case used in the simulations. The studied case, based on a prerun in WRF without any wind farm, has an inflow angle of 222 +/- 2.5 deg, a wind speed at hub height of 9.8 m/s and a near neutral atmosphere. A logarithmic wind shear is used in LES and the turbulence intensity is 5.9%. The WRF simulations use a parameterization for wind farms. The wind farm is treated by the model as a sink of the resolved atmospheric momentum. The total energy extraction and the electrical power are respectively proportional to specified thrust and power coefficients. The generated turbulent kinetic energy are the difference between the total and the electrical power. The LES are performed using the EllipSys3D code applying the actuator disc methodology for representing the presence of the rotors. Synthetic atmospheric turbulence is generated with the Mann model. Both the atmospheric turbulence and the wind shear are introduced using body forces. The production was found to be better estimated in LES. WRF show a slightly higher recovery behind the farm. The internal boundary layer is for the compared simulation setups higher in LES while the wake expansion is about the same in both models. The results from the WRF parameterization could potentially be improved by increasing the grid resolution. For farm to farm interaction a combination of the two methods is found to be of interest.

Place, publisher, year, edition, pages
2015. 012028- p., 012028
, Journal of Physics Conference Series, ISSN 1742-6588 ; 625
National Category
Energy Engineering
URN: urn:nbn:se:uu:diva-261142DOI: 10.1088/1742-6596/625/1/012028ISI: 000358047700028OAI: oai:DiVA.org:uu-261142DiVA: diva2:849838
Wake Conference, JUN 09-11, 2015, Visby, SWEDEN
Swedish National Infrastructure for Computing (SNIC)
Available from: 2015-08-31 Created: 2015-08-31 Last updated: 2016-05-13Bibliographically approved
In thesis
1. Numerical Computations of Wakes Behind Wind Farms
Open this publication in new window or tab >>Numerical Computations of Wakes Behind Wind Farms
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

More and larger wind farms are planned offshore. As the most suitable build sites are limited wind farms will be constructed near to each other in so called wind farm clusters. Behind the wind turbines in these farms there is a disrupted flow of air called a wake that is characterized by reduced wind speed and increased turbulence. These individual turbine wakes combine to form a farm wake that can travel a long distance. In wind farm clusters farm to farm interaction will occur, i.e. the long distance wake from one wind farm will impact the wind conditions for other farms in the surrounding area.

The thesis contains numerical studies of these long distance wakes. In this study Large Eddy Simulations (LES) using an Actuator Disc method (ACD) are used. A prescribed boundary layer is used where the wind shear is introduced using body forces. The turbulence, based on the Mann model, is introduced as fluctuating body forces upstream of the farm. A neutral atmosphere is assumed. The applied method has earlier been used for studies of wake effects inside farms but not for the longer distances needed for farm to farm interaction.

Numerical studies are performed to get better knowledge about the use of this model for long distance wakes. The first study compares the simulation results with measurements behind an existing farm. Three parameter studies are thereafter setup to analyze how to best use the model. The first parameter study examines numerical and physical parameters in the model. The second one looks at the extension of the domain and turbulence as well as the characteristics of the flow far downstream. The third one gathers information on the downstream development of turbulence with different combinations of wind shear and turbulence level. The impact of placing the turbines at different distances from the turbulence plane is also studied. Finally a second study of an existing wind farm is performed and compared with a mesoscale model. The model is shown to be relevant also for studies of long distance wakes. Combining LES with a mesoscale model can be of interest.

Place, publisher, year, edition, pages
Uppsala: Institutionen för geovetenskaper, 2015. 57 p.
, Department of Earth Sciences Licentiate Thesis
Wind turbine, Wind power, Wind farm, Wakes, Long distance wakes, Farm-Farm, Farm to farm interaction, Wind farm cluster, Large Eddy simulations, LES, Actuator disc method, ACD, CFD, Ellipsys3D
National Category
Meteorology and Atmospheric Sciences
urn:nbn:se:uu:diva-255859 (URN)
, Visby (English)
Available from: 2015-08-31 Created: 2015-06-18 Last updated: 2016-02-12Bibliographically approved

Open Access in DiVA

fulltext(1268 kB)72 downloads
File information
File name FULLTEXT01.pdfFile size 1268 kBChecksum SHA-512
Type fulltextMimetype application/pdf

Other links

Publisher's full text

Search in DiVA

By author/editor
Eriksson, OlaBreton, Simon-PhilippeIvanell, Stefan
By organisation
Department of Earth Sciences
Energy Engineering

Search outside of DiVA

GoogleGoogle Scholar
Total: 72 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

Altmetric score

Total: 160 hits
ReferencesLink to record
Permanent link

Direct link