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Euromech 10 th European Turbulence Conference 29 June – 2 July 2004, Trondheim, Norway. An experimental study of bypass transition in plane Couette flow. S. AMALFI, F. LAADHARI & J. F. SCOTT Laboratoire de Mécanique des Fluides et d’Acoustique Unité Mixte de Recherche 5509 - PowerPoint PPT Presentation
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An experimental study of
bypass transition
in plane Couette flow
S. AMALFI, F. LAADHARI & J. F. SCOTTS. AMALFI, F. LAADHARI & J. F. SCOTT
Laboratoire de Mécanique des Fluides et Laboratoire de Mécanique des Fluides et d’Acoustiqued’Acoustique
Unité Mixte de Recherche 5509Unité Mixte de Recherche 550969 134 ECULLY, France69 134 ECULLY, France
Euromech 10 th European Turbulence Conference
29 June – 2 July 2004, Trondheim, Norway
22
Introduction
• Plane Couette flow (PCF) is of particular interest :
simplicity of the basic flow and the absence of linear instability.
• Recent scenario* :
streamwise vortices streaks secondary instabilities turbulence
• The aim of the present study : investigate such a scenario in PCF introducing Counter rotating pairs of streamwise vortices based on optimal criteria.
TransitioTransitionn
Perturbation ratePerturbation rate knowledgeknowledgeOccurrenceOccurrence
in naturein nature
Classicalinfinitesimal
perturbations(≤ 0.1%)
Wellknown
seldomseldom
Bypassfinite perturbations
(≥ 1%)poorly
understood most casesmost cases
• 2 different kinds of transition to turbulence in 2D bounded flows:
*Reddy et al. (1998), J. Fluid Mech., 365, 269-299
33
Outline
• Experimental setup and perturbation generating
system
• Tomography animation and flow characteristics
based on LDA measurements
• Visualization of vortical structures and statistical
analysis based on PIV measurements
• Conclusion and perspectives
44
Experimental setup
Experimental facilities
Tomography and LDA results PIV analysis
• PCF : flow between one or two moving belts
• Very few experimental PCF studies, considering several setup difficulties (moving belts stability, free stream perturbations, etc.)
• Reynolds number of interest is 470 with .walle
U hR
Water
Lx=200 cm Ly=2h=2.6 cm Lz=30 cm
ZOOM
Laminar
Re ≤ 470
Turbulent
Re ≥ 500
Top viewMotor Encoder
55
Experimental facilities
Tomography and LDA results PIV analysis
66
50 mm
5 mm30°
40 mm
Perturbation system based on optimal perturbations*
Experimental facilities
Tomography and LDA results PIV analysis
* Butler & Farrell (1992), Phys. Fluids, 4, 1637-1650
77
Experimental facilities
Tomography and LDA results PIV analysis
plexiglasswall
moving belt
88
Experimental facilities
Tomography and LDA results PIV analysis
99
-4 -3 -2 -1 0 1 2 3 4
-1
-0.5
0
0.5
1
Before injection
Averaged streamwise velocity (cm/s)
Y(cm)
After injection
Experimental facilities
Tomography and LDA results PIV analysis
Time (s)
Y(mm)
cm/sInstantaneous streamwise velocity
1010
• PIV measurements (2 000 snapshots) performed in the transverse
plane. Snapshot size : 26 mm (y) x 96 mm (z) giving two velocity
components : v and w (along y et z).
• Dynamical analysis of structures possible, considering very low
velocities of moving walls (3.6 cm/s) with a 4 Hz frequency
acquisition
• Normalized Angular Momentum* is a good tool to visualize
vortical structures
Visualization of vortical structures
Experimental facilities
Tomography and LDA results PIV analysis
* Michard et al. (1997), 11th Int. Symp. Turbulent Shear Flows, F. Durst, Springer, 278-290
1111
Time
Time (s)
Z
001 ≤ Time (s) ≤ 050
Z(mm
)Y
(mm)
Time (s)
0 100 200 300 400 5000
0.5
1
1.5
2
2.5x 10
-5
Time (s)
Energy(m²/s²)
Time (s)
Z
0 100 200 300 400 5000
0.5
1
1.5
2
2.5x 10
-5
Time (s)
Energy(m²/s²)
Z(mm
)Y
(mm)
Time (s)
050 ≤ Time (s) ≤ 100
Time (s)
Z
0 100 200 300 400 5000
0.5
1
1.5
2
2.5x 10
-5
Time (s)
Energy(m²/s²)
Z(mm
)Y
(mm)
Time (s)
100 ≤ Time (s) ≤ 150
Time (s)
Z
0 100 200 300 400 5000
0.5
1
1.5
2
2.5x 10
-5
Time (s)
Energy(m²/s²)
Z(mm
)Y
(mm)
Time (s)
150 ≤ Time (s) ≤ 200
Time (s)
Z
0 100 200 300 400 5000
0.5
1
1.5
2
2.5x 10
-5
Time (s)
Energy(m²/s²)
Z(mm
)Y
(mm)
Time (s)
200 ≤ Time (s) ≤ 250
Time (s)
Z
0 100 200 300 400 5000
0.5
1
1.5
2
2.5x 10
-5
Time (s)
Energy(m²/s²)
Z(mm
)Y
(mm)
Time (s)
250 ≤ Time (s) ≤ 300
Time (s)
Z
Z(mm
)Y
(mm)
Time (s)
0 100 200 300 400 5000
0.5
1
1.5
2
2.5x 10
-5
Time (s)
Energy(m²/s²)
300 ≤ Time (s) ≤ 350
Time (s)
Z
0 100 200 300 400 5000
0.5
1
1.5
2
2.5x 10
-5
Time (s)
Energy(m²/s²)
Z(mm
)Y
(mm)
Time (s)
350 ≤ Time (s) ≤ 400
Times (s)
Z
Z(mm
)Y
(mm)
Time (s)
0 100 200 300 400 5000
0.5
1
1.5
2
2.5x 10
-5
Time (s)
Energy(m²/s²)
400 ≤ Time (s) ≤ 450
Time (s)
Z
Z(mm
)Y
(mm)
Time (s)
0 100 200 300 400 5000
0.5
1
1.5
2
2.5x 10
-5
Time (s)
Energy(m²/s²)
450 ≤ Time (s) ≤ 500
Experimental facilities
Tomography and LDA results PIV analysis
1212
50 100 150 200 250 300 350 400 450 5000
5
10
15
Time (s)
vR
Experimental facilities
Tomography and LDA results PIV analysis
50 100 150 200 250 300 350 400 450 5000
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
x 10-5
Energy(m²/s²)
Time (s)
2
x
v
dA
R
50 100 150 200 250 300 350 400 450 5000.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
d/h
Time (s)
1313
Conclusion and Perspectives
• First PIV database concerning PCF
• Transient growth of secondary instabilities has been observed
using visualizations and PIV measurements
• Mean size of structures doesn’t play a key role in the transition
process
but vortex intensity does !
• LDA measurements confirming PIV study
• Comparison with other complex cases : Boundary Layer over a
flat plate
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