Investigation into boundary layer transition using wall-resolved large-eddy simulations and modeled inflow turbulence
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Published:2022-05-10
Issue:3
Volume:7
Page:967-990
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ISSN:2366-7451
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Container-title:Wind Energy Science
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language:en
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Short-container-title:Wind Energ. Sci.
Author:
Lobo Brandon ArthurORCID, Schaffarczyk Alois Peter, Breuer MichaelORCID
Abstract
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.
A rather low Reynolds number of Rec=105 is studied at a
fixed angle of attack but under five different turbulence intensities
(TIs) 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.
Publisher
Copernicus GmbH
Subject
Energy Engineering and Power Technology,Renewable Energy, Sustainability and the Environment
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