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The Long distance wake behind Horns Rev I studied using large eddy simulations and a wind turbine parameterization in WRF
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
WeatherTech Scandinavia AB, Uppsala, Sweden.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
WeatherTech Scandinavia AB, Uppsala, Sweden.
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2017 (English)In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 854, article id 012012Article in journal (Refereed) Published
Abstract [en]

The aim of the present paper is to obtain a better understanding of long distance wakes generated by wind farms as a first step towards a better understanding of farm to farm interaction. The Horns Rev I (HR) wind farm is considered for this purpose, where comparisons are performed between microscale Large Eddy Simulations (LES) using an Actuator Disc model (ACD), mesoscale simulations in the Weather Research and Forecasting Model (WRF) using a wind turbine parameterization, production data as well as wind measurements in the wind farm wake. The LES is manually set up according to the wind conditions obtained from the mesoscale simulation as a first step towards a meso/microscale coupling.

The LES using an ACD are performed in the EllipSys3D code. A forced boundary layer (FBL) approach is used to introduce the desired wind shear and the atmospheric turbulence field from the Mann model. The WRF uses a wind turbine parameterization based on momentum sink. To make comparisons with the LESs and the site data possible an idealized setup of WRF is used in this study.

The case studied here considers a westerly wind direction sector (at hub height) of 270 ± 2.5 degrees and a wind speed of 8 ± 0.5 m/s. For both the simulations and the site data a neutral atmosphere is considered. The simulation results for the relative production as well as the wind speed 2 km and 6 km downstream from the wind farm are compared to site data. Further comparisons between LES and WRF are also performed regarding the wake recovery and expansion.

The results are also compared to an earlier study of HR using LES as well as an earlier comparison of LES and WRF. Overall the results in this study show a better agreement between LES and WRF as well as better agreement between simulations and site data.

The procedure of using the profile from WRF as inlet to LES can be seen as a simplified coupling of the models that could be developed further to combine the methods for cases of farm to farm interaction.

Place, publisher, year, edition, pages
2017. Vol. 854, article id 012012
National Category
Meteorology and Atmospheric Sciences
Identifiers
URN: urn:nbn:se:uu:diva-362564DOI: 10.1088/1742-6596/854/1/012012ISI: 000435276400012OAI: oai:DiVA.org:uu-362564DiVA, id: diva2:1253917
Conference
Wake Conference 2017, 30 May to 1 June 2017, Visby, Sweden
Available from: 2018-10-07 Created: 2018-10-07 Last updated: 2019-03-18Bibliographically approved
In thesis
1. Numerical Computations of Wakes Behind Wind Farms: A tool to study Farm to Farm interaction
Open this publication in new window or tab >>Numerical Computations of Wakes Behind Wind Farms: A tool to study Farm to Farm interaction
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

More and larger wind farms are planned offshore. As the most suitable sites to build are limited these new 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 long distances. 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.

This thesis contains numerical studies of these long distance wakes. In these studies 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 the study of farm to farm interaction. Parameter studies are setup to analyze how to best use the model for the study of long distance wakes with regards to 1) numerical and physical parameters in the model, 2) the extension of the domain and turbulence as well as the characteristics of the flow far downstream and 3) the downstream development of turbulence with different combinations of wind shear and turbulence level.

Using an initial simulation setup a wind farm was studied and preliminary results were obtained. These results were subsequently improved upon by applying the simulation setup adjustments indicated in the parameter studies. A comparison with a mesoscale model was also done. The mesoscale model was shown to be relevant for studies of long distance wakes in another study comparing LES and WRF. Finally an idealized farm to farm interaction case was studied with focus on the impact of including the Coriolis force in the simulations.

Combining LES with a mesoscale model is of interest to study further.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. p. 73
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1789
Keywords
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, Prescribed boundary layer, PBL, Forced boundary layer, FBL
National Category
Earth and Related Environmental Sciences
Research subject
Meteorology
Identifiers
urn:nbn:se:uu:diva-379125 (URN)978-91-513-0616-2 (ISBN)
Public defence
2019-06-13, E22, Uppsala universitet - Campus Gotland, Cramérgatan 3, Visby, 10:15 (English)
Opponent
Supervisors
Available from: 2019-04-26 Created: 2019-03-18 Last updated: 2019-06-17

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