an experimental study of bypass transition in plane couette flow n.
Download
Skip this Video
Download Presentation
An experimental study of bypass transition in plane Couette flow

Loading in 2 Seconds...

play fullscreen
1 / 13

An experimental study of bypass transition in plane Couette flow - PowerPoint PPT Presentation


  • 85 Views
  • Uploaded on

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

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'An experimental study of bypass transition in plane Couette flow' - ally


Download Now An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
an experimental study of bypass transition in plane couette flow

Euromech10 th European Turbulence Conference29 June – 2 July 2004, Trondheim, Norway

An experimental study of bypass transition in plane Couette flow

S. AMALFI, F. LAADHARI & J. F. SCOTTLaboratoire de Mécanique des Fluides et d’Acoustique

Unité Mixte de Recherche 5509

69 134 ECULLY, France

slide2

Introduction

  • 2 different kinds of transition to turbulence in 2D bounded flows:
  • 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.

*Reddy et al. (1998), J. Fluid Mech., 365, 269-299

slide3

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
slide4

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 .

Laminar

Motor

Encoder

Top view

Re ≤ 470

ZOOM

Turbulent

Water

Ly=2h=2.6 cm

Re ≥ 500

Lx=200 cm

Lz=30 cm

Experimental facilities

Tomography and LDA results

PIV analysis

Experimental setup

slide5

Experimental facilities

Tomography and LDA results

PIV analysis

slide6

Experimental facilities

Tomography and LDA results

PIV analysis

30°

5 mm

50 mm

40 mm

Perturbation system based on optimal perturbations*

* Butler & Farrell (1992), Phys. Fluids, 4, 1637-1650

slide7

Experimental facilities

Tomography and LDA results

PIV analysis

moving belt

plexiglass

wall

slide8

Experimental facilities

Tomography and LDA results

PIV analysis

slide9

cm/s

Y

(mm)

Time (s)

Before injection

After injection

-1

-0.5

Y

(cm)

0

0.5

1

-4

-3

-2

-1

0

1

2

3

4

Averaged streamwise velocity (cm/s)

Experimental facilities

Tomography and LDA results

PIV analysis

Instantaneous streamwise velocity

slide10

Experimental facilities

Tomography and LDA results

PIV analysis

Visualization of vortical structures

  • 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

* Michard et al. (1997), 11th Int. Symp. Turbulent Shear Flows, F. Durst, Springer, 278-290

slide11

Z

Z

Z

Z

Z

Z

Z

Z

Z

Z

Time (s)

Time (s)

Time (s)

Time (s)

Time (s)

Time (s)

Times (s)

Time (s)

Time (s)

Time (s)

Z

(mm)

Z

(mm)

Z

(mm)

Z

(mm)

Z

(mm)

Z

(mm)

Z

(mm)

Z

(mm)

Z

(mm)

Z

(mm)

Time (s)

Time (s)

Time (s)

Time (s)

Time (s)

Time (s)

Time (s)

Time (s)

Time (s)

Time (s)

Y

(mm)

Y

(mm)

Y

(mm)

Y

(mm)

Y

(mm)

Y

(mm)

Y

(mm)

Y

(mm)

Y

(mm)

Y

(mm)

300 ≤ Time (s) ≤ 350

400 ≤ Time (s) ≤ 450

350 ≤ Time (s) ≤ 400

200 ≤ Time (s) ≤ 250

050 ≤ Time (s) ≤ 100

250 ≤ Time (s) ≤ 300

150 ≤ Time (s) ≤ 200

450 ≤ Time (s) ≤ 500

100 ≤ Time (s) ≤ 150

Energy

(m²/s²)

Energy

(m²/s²)

Energy

(m²/s²)

Energy

(m²/s²)

Energy

(m²/s²)

Energy

(m²/s²)

Energy

(m²/s²)

Energy

(m²/s²)

Energy

(m²/s²)

Energy

(m²/s²)

Time (s)

Time (s)

Time (s)

Time (s)

Time (s)

Time (s)

Time (s)

Time (s)

Time (s)

Time (s)

Experimental facilities

Tomography and LDA results

PIV analysis

Time

001 ≤ Time (s) ≤ 050

slide12

Energy

(m²/s²)

Time (s)

d/h

Time (s)

Time (s)

Experimental facilities

Tomography and LDA results

PIV analysis

slide13

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