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Research articles 23 Apr 2018

Research articles | 23 Apr 2018

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This discussion paper is a preprint. A revision of the manuscript is under review for the journal Wind Energy Science (WES).

Blind test comparison on the wake behind a yawed wind turbine

Franz Mühle1, Jannik Schottler2, Jan Bartl3, Romain Futrzynski4, Steve Evans4, Luca Bernini5, Paolo Schito5, Martín Draper6, Andrés Guggeri6, Elektra Kleusberg7, Dan S. Henningson7, Michael Hölling2, Joachim Peinke2,8, Muyiwa S. Adaramola1, and Lars Sætran3 Franz Mühle et al.
  • 1Faculty of Environmental Sciences and Natural Resource Management, Norwegian University of Life Sciences, Ås, Norway
  • 2ForWind - Center for Wind Energy, Institute of Physics, University of Oldenburg, Oldenburg, Germany
  • 3Department of Energy and Process Engineering, Norwegian University of Science and Technology, Trondheim, Norway
  • 4Siemens PLM Software, London, United Kingdom
  • 5Department of Mechanical Engineering, Politecnico di Milano, Milan, Italy
  • 6Facultad de Ingeniería, Universidad de la República, Montevideo, Uruguay
  • 7Linné FLOW Centre and Swedish e-Science Research Centre (SeRC), Department of Mechanics, KTH Royal Institute of Technology, Stockholm, Sweden
  • 8Fraunhofer IWES, Oldenburg, Germany

Abstract. This article summarizes the results of a fifth Blind test workshop, which was held in Visby, Sweden, in May 2017. This study compares the numerical predictions of the wake flow behind a model wind turbine operated in yaw to experimental wind tunnel results. Prior to the work shop, research groups were invited to predict the turbines' performances and wake flow properties using computational fluid dynamics (CFD) methods. For this purpose, the power, thrust and yaw moments for a 30° yawed model turbine as well as the wake's mean and turbulent streamwise and vertical flow components were measured in the wind tunnel at the Norwegian University of Science and Technology (NTNU). In order to increase the complexity, a non-yawed downstream turbine was added in a second test case, while a third test case challenged the modelers with a new rotor and turbine geometry.

Four participants submitted predictions using different flow solvers, three of which were based on Large Eddy Simulations (LES) while another one used an Improved Delayed Detached Eddy Simulation (IDDES) model. The performance of a single yawed turbine was fairly well predicted by all simulations, both in the first and third test case. The scatter in the downstream turbine's performance predictions in the second test case, however, was found to be significantly larger. The complex asymmetric shape of the mean streamwise and vertical velocity was generally well predicted by all the simulations for all test cases. The largest improvement with respect to previous Blind tests is the good prediction of the levels of turbulent kinetic energy in the wake, even for the complex case of yaw misalignment. These very promising results confirm the mature development stage of LES/DES simulations for wind turbine wake modeling, while competitive advantages might be obtained by faster computational methods.

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