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Harvard
Saraf, A. (2016) Large Eddy Simulation of transitional flow over a flat plate. Göteborg : Chalmers University of Technology (Diploma work - Department of Applied Mechanics, Chalmers University of Technology, Göteborg, Sweden, nr: 2016:67).
BibTeX
@mastersthesis{
Saraf2016,
author={Saraf, Abishek},
title={Large Eddy Simulation of transitional flow over a flat plate},
abstract={The transition of the laminar boundary layer to turbulence in the free stream is
of major importance in turbomachinery flows. Transition in the boundary layer
has a big impact on flow parameters such as skin friction coefficient and shape
factor thereby affecting the design and development process. It is known that the
boundary-layer transition is affected by properties of the free-stream turbulence such
as its anisotropy, length scale and its intensity. In the present thesis a Large-Eddy
Simulation (LES) has been performed of a zero pressure gradient flat-plate boundary
layer undergoing transition to turbulence under free-stream turbulence at a level of
6%. In the current work the bypass transition is defined as a superposition of the Blasius
layer with freestream continuous isotropic turbulence at an initial intensity level
of 6%. An effort is made to capture the length and position of boundary layer transition
over the flat plate and a subsequent comparison of the skin friction coefficient
and shape factor were made with the experimental data. A finite volume method
based in-house solver in Fortran, namely CALC-LES, is used for performing the
simulations. The solver of CALC-LES is based on a geometric multigrid algorithm
to solve the pressure (poisson) equation. Three different subgrid scale (SGS) models
are used for performing comparative studies – the Smargorinsky-Lilly model, the
Wall-adapting local eddy-viscosity (WALE) model and the Scale-similarity model.
The experimental data for the skin friction coefficient and shape factor were used as
a basis to ascertain whether the present simulation manages to capture transition.
The present simulations fail to capture the transition appropriately in the boundary
layer over the flat plate. The dimensionless coefficients, namely the skin friction
coefficient and the shape factor are not in the exact accordance with the experimental
data. The mesh independence study showed that the stream-wise resolution
hardly played any role in the transition. The study of the resolved Reynolds stress
components in the boundary layer revealed that the stream-wise stress component
decreased in magnitude significantly, but it doesn’t get distributed into the other
components. As a result transition is not observed. Upon further inspection of the
turbulent kinetic energy peak showed that probably the stream-wise streaks grow,
but either they were not big enough to trigger transition or there was no continuous
forcing provided by the free-stream turbulence to trigger transition. It is not known
what aspect of the current LES simulations are at fault but in the light of the general
level of agreement obtained, we conclude that,the the simulation qualitatively
mimics the real boundary layer even though precise quantitative agreement is not
found for all variables.},
publisher={Institutionen för tillämpad mekanik, Strömningslära, Chalmers tekniska högskola},
place={Göteborg},
year={2016},
series={Diploma work - Department of Applied Mechanics, Chalmers University of Technology, Göteborg, Sweden, no: 2016:67},
keywords={CFD, LES, boundary layer transition, bypass, FST, flat plate},
}
RefWorks
RT Generic
SR Electronic
ID 248798
A1 Saraf, Abishek
T1 Large Eddy Simulation of transitional flow over a flat plate
YR 2016
AB The transition of the laminar boundary layer to turbulence in the free stream is
of major importance in turbomachinery flows. Transition in the boundary layer
has a big impact on flow parameters such as skin friction coefficient and shape
factor thereby affecting the design and development process. It is known that the
boundary-layer transition is affected by properties of the free-stream turbulence such
as its anisotropy, length scale and its intensity. In the present thesis a Large-Eddy
Simulation (LES) has been performed of a zero pressure gradient flat-plate boundary
layer undergoing transition to turbulence under free-stream turbulence at a level of
6%. In the current work the bypass transition is defined as a superposition of the Blasius
layer with freestream continuous isotropic turbulence at an initial intensity level
of 6%. An effort is made to capture the length and position of boundary layer transition
over the flat plate and a subsequent comparison of the skin friction coefficient
and shape factor were made with the experimental data. A finite volume method
based in-house solver in Fortran, namely CALC-LES, is used for performing the
simulations. The solver of CALC-LES is based on a geometric multigrid algorithm
to solve the pressure (poisson) equation. Three different subgrid scale (SGS) models
are used for performing comparative studies – the Smargorinsky-Lilly model, the
Wall-adapting local eddy-viscosity (WALE) model and the Scale-similarity model.
The experimental data for the skin friction coefficient and shape factor were used as
a basis to ascertain whether the present simulation manages to capture transition.
The present simulations fail to capture the transition appropriately in the boundary
layer over the flat plate. The dimensionless coefficients, namely the skin friction
coefficient and the shape factor are not in the exact accordance with the experimental
data. The mesh independence study showed that the stream-wise resolution
hardly played any role in the transition. The study of the resolved Reynolds stress
components in the boundary layer revealed that the stream-wise stress component
decreased in magnitude significantly, but it doesn’t get distributed into the other
components. As a result transition is not observed. Upon further inspection of the
turbulent kinetic energy peak showed that probably the stream-wise streaks grow,
but either they were not big enough to trigger transition or there was no continuous
forcing provided by the free-stream turbulence to trigger transition. It is not known
what aspect of the current LES simulations are at fault but in the light of the general
level of agreement obtained, we conclude that,the the simulation qualitatively
mimics the real boundary layer even though precise quantitative agreement is not
found for all variables.
PB Institutionen för tillämpad mekanik, Strömningslära, Chalmers tekniska högskola,
T3 Diploma work - Department of Applied Mechanics, Chalmers University of Technology, Göteborg, Sweden, no: 2016:67
LA eng
LK http://publications.lib.chalmers.se/records/fulltext/248798/248798.pdf
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