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Uranga 2006 Masters Defense turbulence ppt
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Transcript of Uranga 2006 Masters Defense turbulence ppt
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Assessment of Turbulence Modeling for Compressible Flow
Around Stationary and Oscillating Cylinders
by Alejandra Uranga
Supervisors: Drs Nedjib Djilali and Afzal Suleman Dept. of Mechanical Engineering - University of Victoria
August 21, 2006
A p p l i e d V e h i c l e
Technologies
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Outline
Introduction
Simulation Methodology
Stationary Cylinder
Oscillating Cylinder
Conclusions
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Introduction
Periodic pattern of counter-rotating vortices caused by unsteady separation from a bluff body
Krmn Vortex Street
Introduction Methodology Stationary Oscillating Conclusions
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Introduction
Periodic pattern of counter-rotating vortices caused by unsteady separation from a bluff body
Krmn Vortex Street
Introduction Methodology Stationary Oscillating Conclusions
NASA satellite image 1999
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Introduction
Interaction between 3 shear layers - Boundary layer - Free shear layer - Wake
Flow Around a Circular Cylinder
Introduction Methodology Stationary Oscillating Conclusions
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Introduction
Interaction between 3 shear layers - Boundary layer - Free shear layer - Wake
Flow Around a Circular Cylinder
Introduction Methodology Stationary Oscillating Conclusions
Transition to turbulence in - Wake ReD 200 400 - Free Shear layer ReD 400 150x103 - Boundary layer ReD 150x103 8x106
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Introduction
Simulation of turbulent flow around circular cylinders -Stationary ReD = 3900 -Oscillating ReD = 3600
Compare accuracy of turbulence models using same numerical procedure with respect to experiments
and other simulations
Scope
Introduction Methodology Stationary Oscillating Conclusions
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Methodology
Numerical Simulation of Turbulent Flows
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Methodology
Example: Incompressible Momentum Equation
Applying an average or filter operator (overbar) to the momentum equation yields
The terms , , are solved for
The cross terms are unknown closure problem
Introduction Methodology Stationary Oscillating Conclusions
The Need for Turbulence Models
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Methodology
Introduction Methodology Stationary Oscillating Conclusions
Simulation of Turbulence
DNS Direct Numerical
Simulation
Solve all Scales
very thin grid required
ui
URANS Unsteady
Reynolds Averaged Navier-Stokes
(One-point closure)
mean fluctuating
Solve mean quantities
Model Reynolds stresses
u i
LES Large Eddy Simulation
large scale Subgrid-Scale
Solve large scale eddies
Model subgrid-scale stress
u i
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Methodology
URANS -One equation Spalart-Allmaras -K-tau Speziale et al.
Large Eddy Simulation (LES) -Smagorinsky-Lilly
Very Large Eddy Simulation (VLES) -Adaptive k-tau Magagnato & Gabi (uses a URANS type subgrid-scale model)
Introduction Methodology Stationary Oscillating Conclusions
Turbulence Models Considered
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Methodology
SPARC Structured PArallel Research Code
Finite Volume, Cell Centered, Block-Structured, Multigrid
Simulations are 3D Unsteady Compressible Viscous
Introduction Methodology Stationary Oscillating Conclusions
Computational Code
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Stationary Cylinder
Stationary Circular Cylinder in a Uniform Flow
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Stationary Cylinder
Cylinder diameter D = 1m Flow velocity U0 = 68.63m/s Mach number Mach 0.2 Reynolds number ReD = 3900
Problem Setup
Introduction Methodology Stationary Oscillating Conclusions
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Stationary Cylinder
2D figures: x-y plane at span center
Computational Domain
Introduction Methodology Stationary Oscillating Conclusions
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Stationary Cylinder URANS : Average Fields
Introduction Methodology Stationary Oscillating Conclusions
SA Sp
u/U0
zD/U0
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Stationary Cylinder URANS : Average Streamlines
Introduction Methodology Stationary Oscillating Conclusions
SA Sp
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Stationary Cylinder URANS : Average Profiles
Introduction Methodology Stationary Oscillating Conclusions
u/U0 at x/D = 1.54
cp around cylinder
cf around cylinder
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Stationary Cylinder LES-VLES : Streamlines
Introduction Methodology Stationary Oscillating Conclusions
LES VLES
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Stationary Cylinder LES-VLES : Average Fields
Introduction Methodology Stationary Oscillating Conclusions
LES VLES
u/U0
zD/U0
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Stationary Cylinder LES-VLES : Average Profiles
Introduction Methodology Stationary Oscillating Conclusions
u/U0 at x/D=1.54
cp around cylinder
cf around cylinder
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Stationary Cylinder 3-Dimensionality
Streamwise velocity iso-surfaces
Introduction Methodology Stationary Oscillating Conclusions
URANS Sp LES
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Stationary Cylinder Comparison
Introduction Methodology Stationary Oscillating Conclusions
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Oscillating Cylinder
Circular Cylinder in Cross-Flow Oscillations
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Oscillating Cylinder
Vertical sinusoidal motion
2D URANS k-tau Speziale
Reynolds number 3600
Lock-in: vortex shedding frequency matches cylinder motion frequency
Motion and Cases
Introduction Methodology Stationary Oscillating Conclusions
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Oscillating Cylinder URANS Sp Fields
Introduction Methodology Stationary Oscillating Conclusions
zD/U0 u/U0
Case IV fc / f0 = 0.800
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Oscillating Cylinder Lock-in
Introduction Methodology Stationary Oscillating Conclusions
46%40%
2%
1%
63%
32%
motion frequency fc/f0
sheddi
ng f
requ
ency
fS/f 0
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Conclusions
Summary and Further Work
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Conclusions
comparison of results from different turbulence models with same numerical procedure
Spalart-Allmaras model - error in separation point flow remains attached too long small recirculation zone low back pressure large drag
- Accurate Strouhal number
Introduction Methodology Stationary Oscillating Conclusions
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Conclusions K-tau Speziale model - Good mean global quantities Strouhal number, drag, back pressure, separation point velocity profiles along the wake
LES and VLES - reveal secondary eddies - LES resolves dynamics in boundary layer
Oscillating Cylinder
- No other numerical results in same regime - Lock-in over large range of motion frequencies - Further investigation required
Introduction Methodology Stationary Oscillating Conclusions
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Conclusions
Better averages on LES and VLES
LES with Dynamic and Dynamic Mixed subgrid-scale models
LES of oscillating cylinder
Further Work
Introduction Methodology Stationary Oscillating Conclusions
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Questions