Preprints
https://doi.org/10.5194/wes-2021-30
https://doi.org/10.5194/wes-2021-30

  28 Apr 2021

28 Apr 2021

Review status: a revised version of this preprint is currently under review for the journal WES.

Investigation Into Boundary Layer Transition Using Wall-Resolved LES and Modeled Inflow Turbulence

Brandon Arthur Lobo1, Alois Peter Schaffarczyk1, and Michael Breuer2 Brandon Arthur Lobo et al.
  • 1Mechanical Engineering Department, Kiel University of Applied Sciences, D-24149 Kiel, Germany
  • 2Professur für Strömungsmechanik, Helmut-Schmidt-Universität Hamburg, D-22043 Hamburg, Germany

Abstract. The objective of the present paper is to investigate the transition scenario of the flow around a typical section of a wind turbine blade exposed to different levels of inflow turbulence. As a first step towards this objective, a rather low Reynolds number of Rec = 105 is studied at a fixed angle of attack but under five different turbulence intensities (TI) up to TI = 11.2 %. Using wall-resolved large-eddy simulations combined with an inflow procedure relying on synthetically generated turbulence and a source-term formulation for its injection within the computational domain, relevant flow features such as the separation bubble, inflectional instabilities and streaks can be investigated. The study shows that the transition scenario significantly changes with rising TI, where the influence of inflectional instabilities due to an adverse pressure gradient decreases, while the influence of streaks increases resulting in a shift from the classical scenario of natural transition to bypass transition. The primary instability mechanism in the separation bubble is found to be inflectional and its origin is traced back to the region upstream of the separation. Thus, the inviscid inflectional instability of the separated shear layer is an extension of the instability of the attached adverse pressure gradient boundary layer observed upstream. The boundary layer is evaluated to be receptive to external disturbances such that the initial energy within the boundary layer is proportional to the square of the turbulence intensity. Boundary layer streaks were found to influence the instantaneous separation location depending on their orientation. A varicose mode of instability is observed on the overlap of the leading edge of a high-speed streak with the trailing edge of a low-speed streak. The critical amplitude of this instability was analyzed to be about 32 % of the free-stream velocity.

Brandon Arthur Lobo et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on wes-2021-30', Anonymous Referee #1, 19 Jun 2021
    • AC1: 'Reply on RC1', Brandon Lobo, 02 Jul 2021
  • RC2: 'Comment on wes-2021-30', Anonymous Referee #2, 29 Sep 2021
    • AC2: 'Reply on RC2', Brandon Lobo, 06 Oct 2021

Brandon Arthur Lobo et al.

Brandon Arthur Lobo et al.

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Short summary
This research involves studying the flow around the section of a wind turbine blade albeit at a lower Reynolds number or flow speed using wall-resolved large-eddy simulations, a form of computer simulation that resolves the important scales of the flow. Among the many interesting results, it is shown that the energy entering the boundary layer around the airfoil or section of the blade is proportional to the square of the incoming flow turbulence intensity.