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Wake meandering statistics of a model wind turbine: Insights gained by large eddy simulations

Daniel Foti, Xiaolei Yang, and Michele Guala

Fotis Sotiropoulos*

  • St. Anthony Falls Laboratory, University of Minnesota, Minneapolis, Minnesota 55455, USA

  • Department of Civil Engineering, College of Engineering and Applied Science, Stony Brook University, Stony Brook, New York 11794, USA

  • *Corresponding author: fotis.sotiropoulos@stonybrook.edu
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Phys. Rev. Fluids 1, 044407 – Published 16 August, 2016

DOI: https://doi.org/10.1103/PhysRevFluids.1.044407

Abstract

Wind tunnel measurements in the wake of an axial flow miniature wind turbine provide evidence of large-scale motions characteristic of wake meandering [Howard et al., Phys. Fluids 27, 075103 (2015)]. A numerical investigation of the wake, using immersed boundary large eddy simulations able to account for all geometrical details of the model wind turbine, is presented here to elucidate the three-dimensional structure of the wake and the mechanisms controlling near and far wake instabilities. Similar to the findings of Kang et al. [Kang et al., J. Fluid Mech. 744, 376 (2014)], an energetic coherent helical hub vortex is found to form behind the turbine nacelle, which expands radially outward downstream of the turbine and ultimately interacts with the turbine tip shear layer. Starting from the wake meandering filtering used by Howard et al., a three-dimensional spatiotemporal filtering process is developed to reconstruct a three-dimensional meandering profile in the wake of the turbine. The counterwinding hub vortex undergoes a spiral vortex breakdown and the rotational component of the hub vortex persists downstream, contributing to the rotational direction of the wake meandering. Statistical characteristics of the wake meandering profile, along with triple decomposition of the flow field separating the coherent and incoherent turbulent fluctuations, are used to delineate the near and far wake flow structures and their interactions. In the near wake, the nacelle leads to mostly incoherent turbulence, while in the far wake, turbulent coherent structures, especially the azimuthal velocity component, dominate the flow field.

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Phys. Rev. Fluids 1, 044407– Published 16 August, 2016
  • Received 2 March 2016
Article part of CHORUS

©2016 American Physical Society

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