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Analysis of long distance wakes behind a row of turbines – a parameter study
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.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
2014 (English)In: Science of Making Torque from Wind, 2014, 012152- p.Conference paper, Published paper (Refereed)
Abstract [en]

Large Eddy Simulations (LES) of the long distance wake behind a row of 10 turbines are conducted to predict wake recovery. The Navier-Stokes solver EllipSys3D is used in combination with the actuator disc concept. Neutral atmospheric conditions are assumed in combination with synthetic turbulence using the Mann method. Both the wind shear profile and turbulence are introduced into the flow field using body forces. Previous simulations using the same simulation method to model the Horns Rev wind farm showed a higher wake recovery at long distances compared to measurements. The current study investigates further the sensitivity to parameters such as the grid resolution, Reynolds number, the turbulence characteristics as well as the impact of using different internal turbine spacings. The clearest impact on the recovery behind the farm could be seen from the background turbulence. The impact of the wind shear on the turbulence level in the domain needs further studies. A lower turbulence level gives lower wake recovery as expected. A lower wake recovery can also be seen for a higher grid resolution. The Reynolds number, apart from when using a very low value, has a small impact on the result. The variation of the internal spacing is seen to have a relatively minor impact on the farm wake recovery.

Place, publisher, year, edition, pages
2014. 012152- p.
Series
Journal of Physics Conference Series, ISSN 1742-6588 ; 524
National Category
Physical Sciences Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:uu:diva-237704DOI: 10.1088/1742-6596/524/1/012152ISI: 000344193600152OAI: oai:DiVA.org:uu-237704DiVA: diva2:768585
Conference
5th Science of Making Torque from Wind Conference, JUN 18-20, 2014, Tech Univ Denmark, Copenhagen, DENMARK
Funder
Swedish National Infrastructure for Computing (SNIC)StandUp for Wind
Available from: 2014-12-04 Created: 2014-12-04 Last updated: 2017-02-03Bibliographically 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.
Series
Department of Earth Sciences Licentiate Thesis
Keyword
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
Identifiers
urn:nbn:se:uu:diva-255859 (URN)
Presentation
, Visby (English)
Opponent
Supervisors
Available from: 2015-08-31 Created: 2015-06-18 Last updated: 2016-02-12Bibliographically approved

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Eriksson, OlaNilsson, KarlBreton, Simon-PhilippeIvanell, Stefan

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