% IMPORTANT: The following is UTF-8 encoded. This means that in the presence
% of non-ASCII characters, it will not work with BibTeX 0.99 or older.
% Instead, you should use an up-to-date BibTeX implementation like “bibtex8” or
% “biber”.
@PHDTHESIS{Albers:820772,
author = {Albers, Marian},
othercontributors = {Schröder, Wolfgang and Noack, Bernd R.},
title = {{N}umerical analysis of active drag reduction for turbulent
airfoil flow; 1. {A}uflage},
school = {RWTH Aachen University},
type = {Dissertation},
address = {München},
publisher = {Verlag Dr. Hut},
reportid = {RWTH-2021-05816},
isbn = {978-3-8439-4806-7},
pages = {xvi, 120 Seiten : Illustrationen},
year = {2021},
note = {Dissertation, RWTH Aachen University, 2021},
abstract = {Turbulent boundary layers over slender bodies generate a
substantial drag force, which can make up a large share of
the overall drag of large aircraft in cruise flight or high
speed trains. Active drag reduction approaches, which
introduce external energy into the system, are capable of
considerably reducing the friction forces attributed to
turbulent wall-bounded flows. Among the numerous active
techniques, spanwise traveling transversal surface waves is
a successful approach for canonical flows, e.g., turbulent
channel flow. However, several important questions have not
been addressed adequately, yet. Due to a large parameter
space of the actuation parameters, their impact on drag
reduction was not studied extensively, yet. Furthermore, the
technique has not been applied to more complex flows like
the turbulent flow around an airfoil. Therefore,
high-resolution large-eddy simulations are conducted to
study active drag reduction of turbulent flat plate boundary
layer as well as an airfoil flow, where drag reduction via
traveling transversal surface waves is applied.
Zero-pressure gradient turbulent boundary layer flow is the
basis for a large parametric study of spanwise traveling
transversal surface waves, which is presented first. The
results show a maximum drag reduction of −31 $\%$ and net
power saving of up to −10 $\%.$ Especially for large
wavelengths, a Stokes-layer-type scaling is found to
correlate well with the reduction of the wall-shear stress.
The breakdown of the scaling beyond a wavelength-dependent
maximum is connected to an enhanced spanwise flow, which
leads to separation effects and increased turbulent mixing.
An optimum actuation period in inner units is determined and
the oscillating spanwise shear is identified, which is
caused by the secondary flow field and connected to the drag
reduced state. Similar mechanisms can be observed for
spanwise wall oscillations. The investigation is then
extended to swept flow, such that transversal surface waves
traveling partially with or against the mean flow are
considered. For small sweep angles only a minor decrease of
the drag reduction is found for partially downstream
traveling waves. Furthermore, the drag-reduced near-wall
flow persists even for larger sweep angles. For partially
upstream traveling waves, a more diverse flow is observed
where a drag-reduced near-wall flow coexists with amplified
turbulence in the outer boundary layer. Finally, spanwise
traveling transversal surface waves are applied to the
turbulent flow around an airfoil wing section. The actuation
of large parts of the upper and lower surface leads to a
significantly reduced friction and total drag and a
moderately increased lift. Strong local reductions of the
wall-shear stress are also obtained for parts of the flow
which experience a strong adverse pressure gradient. The
decreased boundary layer height and damped turbulence
persist well beyond the actuated region, which leads to an
actuation effect in the wake region.},
cin = {415110},
ddc = {620},
cid = {$I:(DE-82)415110_20140620$},
typ = {PUB:(DE-HGF)11 / PUB:(DE-HGF)3},
url = {https://publications.rwth-aachen.de/record/820772},
}
guest ::