Bechmann, Andreas

Berg, Jacob

Courtney, Michael

Hristov, Yavor V.

Koblitz, Tilman

Online Research Database In Technology

                       General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.  • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal   If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.     Downloaded from orbit.dtu.dk on: Dec 20, 2017In the wake of Bolund: Benakanahalli - Stratification and complex terrainBerg, Jacob; Bechmann, Andreas; Courtney, Michael; Koblitz, Tilman; Hristov, Yavor V.Publication date:2012Document VersionPublisher's PDF, also known as Version of recordLink back to DTU OrbitCitation (APA):Berg, J., Bechmann, A., Courtney, M., Koblitz, T., & Hristov, Y. V. (2012). In the wake of Bolund: Benakanahalli -Stratification and complex terrain. Poster session presented at EWEA 2012 - European Wind EnergyConference & Exhibition, Copenhagen, Denmark.BENAKANAHALLI: IN THE WAKE OF BOLUND   Stratification and Complex Terrain     Jacob Berg (1), Andreas Bechman (1), Michael Courtney (1) and Søren Holm Mogensen (2)  (1) DTU Wind Energy, Risø campus, Denmark (2) Vestas Technology R&D , Denmark  Email: jbej@dtu.dk  PO.ID  107   In early 2010 a new field experiment, close to the village of Benakanahalli, focusing on micro meteorological properties important for wind energy were conducted in the region of Karnataka, India. The field experiment is the natural successor to the Bolund Hill experiment (Boundary Layer Meteorology 141, p. 219 & p. 245, 2011):  The Bolund measurement campaign performed near the Risø campus of DTU Wind Energy, in 2009 provided significant insight into flow in complex terrain and has proven very suitable for benchmarking of models. Even though up-scaling is permitted to some degree, the 12 m tall peninsula, the Bolund Hill, is still too simple for many purposes; it lacks atmospheric stratification and the Coriolis effects. In addition the wake of Bolund was very poorly resolved. The present field campaign focus on exactly those things. i.e. the flow is altered by both the presence of complex terrain and atmospheric stratification and we are thus able to study the combined effects of these upon the flow. This study which should be much welcomed in the wind energy community, since a large part of turbines today are erected exactly at places where these effects are non-negligible.   Introduction Outlook      Preliminary data: Roadmap of four days in February 2010 with reversed afternoon surface flow in front and behind of the hill           EWEA 2012, Copenhagen, Denmark: Europe’s Premier Wind Energy Event  A field experiment at  14°10’ 34” N,   75°50’ 29” E Five 80m masts were erected near and on a long almost two-dimensional 120m natural ridge with slopes of around 35 degrees. Equipped with sonic anemometers in five different heights, both the mean flow and the turbulence are well resolved. In addition temperature sensors were mounted on the upstream mast. Together with measurements of heat fluxes from the sonic anemometers a good estimate of the thermal stratification is thus obtained. Three mast were positioned in the wake of the hill giving us the opportunity to estimate its size and hence the recovery length of the wind speed. For estimation of the boundary layer height a ceilometer was also installed. Due to shortage of electrical power all mast instruments were run by solar power. Data were transmitted by satellite connection to DTU Wind Energy, Denmark.  Key dimensionless numbers:  Fr~0.2 (night), Ro~50 (night), Ro~400 (day)       Like the Bolund Hill, the Benakanahalli site provides excellent opportunities for testing existing and developing new flow models for use in wind energy. The added complexity of the day - night  influence through stability is an extra challenge compared to the Bolund case.  During the measurement campaign a WRF meso-scale model has been running covering the site and surroundings. We thus know  the meteorology on even larger scales and hence the necessary boundary conditions for successfully mimicking the flow  around the Benanakanahalli site. From a boundary layer meteorological point of view, the measurements also give hope for new insights into micro meteorological behavior at low  latitudes in complex terrain..    N 

In the wake of Bolund: Benakanahalli - Stratification and complex terrain

                       General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.  • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal   If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.     Downloaded from orbit.dtu.dk on: Dec 20, 2017In the wake of Bolund: Benakanahalli - Stratification and complex terrainBerg, Jacob; Bechmann, Andreas; Courtney, Michael; Koblitz, Tilman; Hristov, Yavor V.Published in:Proceedings of EWEA 2012 - European Wind Energy Conference &amp; ExhibitionPublication date:2012Document VersionPublisher's PDF, also known as Version of recordLink back to DTU OrbitCitation (APA):Berg, J., Bechmann, A., Courtney, M., Koblitz, T., & Hristov, Y. V. (2012). In the wake of Bolund: Benakanahalli -Stratification and complex terrain. In Proceedings of EWEA 2012 - European Wind Energy Conference &Exhibition European Wind Energy Association (EWEA).ABSTRACT ID:   36Theme: RESOURCE ASSESSMENT  Topic:  Advances in measuring techniques for resource assessmentIN THE WAKE OF BOLUND: BENAKANAHALLI - STRATIFICATION AND COMPLEX TERRAIN Jacob Berg(1)  (F)  (P) Andreas Bechmann(1) Michael S. Courtney(1) TIlman Koblitz(1) Yavor V.  Hristov(2) (1) DTU Wind Energy, Roskilde, Denmark(2) Vestas Technology R&D , Randers, DenmarkIntroductionMicro-scale numerical flow models are the cornerstones of wind energy site assessment. With more and more new sites in complex terrain the modelrequirements have increased dramatically in the recent years. This has been followed by a demand of full scale measurement campaigns designed tobenchmark the models in complex terrain. The Bolund measurement campaign performed near Risø DTU, in 2009 (Boundary Layer Meteorology 141,p. 219 & p. 245, 2011) provided significant insight into flow in complex terrain and has proven very suitable for benchmarking of models. Even thoughup-scaling is permitted to some degree, the 12 m tall peninsula, the Bolund Hill, is still too simple for many purposes; it lacks atmospheric stratificationand the Coriolis effects. In addition the wake of Bolund was very poorly resolved. Though an optimal test case for micro-scales model Bolund is not a realistic wind turbine site. With this in mind a new measurement campaign was planned and conducted as a joint collaboration between Risø DTU andVestas Technology R&D.ApproachMain body of abstractIn this presentation we will present the first results of a new large scale measurement campaign where the flow is altered by both the presence ofcomplex terrain and atmospheric stratification. Whereas studies of complex terrain have been done mainly in neutral conditions and studies ofatmospheric stratification in primarily flat terrain, a study where also the combined non-linear effects are studied should be much welcomed in the windenergy community, since a large part of turbines today are erected exactly at places where these are non-negligible.  	The name of the campaign is Benakanahalli.  The measurements were conducted  from February to April 2010 in the province of karnataka in Indiaclose to the village of Benakanahalli. Five 80m masts were erected near and on a long almost two-dimensional 120m natural ridge with slopes ofaround 30 degrees. The hill type is very common in wind energy, which can easily be verified by a short drive in the area where a huge amount of windturbines are erected on similar hills.  	Equipped with sonic anemometers in five different heights, both the mean flow and the turbulence are well resolved. In addition temperature sensorswere mounted on the upstream mast. Together with measurements of heat fluxes from the sonic anemometers a good estimate of the thermalstratification is thus obtained. Three mast were positioned in the wake of the hill giving us the opportunity to estimate its size and hence the recoverylength of the wind speed. 	ConclusionWe will show the first comparison with a numerical micro-scale model, the Risø DTU EllipSys3D RANS k-epsilon model, which manage to capturemany of the interesting features happening as a result of the interplay between complex terrain, thermal stratification and Coriolis force.

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In the wake of Bolund: Benakanahalli - Stratification and complex terrain

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