Embed Size (px)
Citation preview
06.06.2011
PIV and PTV in Multiphase Flows Gustavo A. Zarruk
06.06.2011
At IFE we have DPIV and Time-Resolved DPIV What is it? • Non-intrusive measurement
technique • Excellent temporal and spatial
resolution • High repetition laser • High speed camera • Digital image processing • Fancy mathematics and statistics
Frame rate vs Resolution Typical 5400 @ 1024x1024 pixels Maximum 675,000 @ 64x16 pixels
06.06.2011
Time Resolved Particle Image Velocimetry (TRPIV)
Fundamentals of Digital Particle Image Velocimetry - Westerweel (1997)
• Fluid Velocity inferred from ideal tracer particles • Velocity measured indirectly from particle displacement • Tracer particles are described in terms of a pattern • 2D – TRPIV
• Cross section of the flow is illuminated with a thin light sheet (Dual pulsed laser)
• Tracer particles in the light sheet are projected onto a recording medium ~ CCD or CMOS high speed camera - TRPIV
• Image pair acquired in a short period of time dt~Ο (1µs) • FFT-based cross-correlation performed on small interrogation
windows • Correlation peak ~ particle pattern displacement, ds
06.06.2011
PIV Schematic
06.06.2011
How does it look?
Bad PIV but good for explaining
06.06.2011
PIV Velocity Estimation
06.06.2011
Partickle Tracking A hybrid digital particle tracking velocimetry technique – Cowen & Monismith (1997)
DPIV results
Particle Tracking Algorithm
I1(t) I2(t+dt)
New particle Tracked particle
Out of field of view
06.06.2011
Results sample Fluid Velocity and Vorticity
06.06.2011
PIV @ IFE: Particle flow in pipelines Raw Images Fluid Velocity
06.06.2011
Final result
Poelma et. al. (2006)
Fluid and Particle Velocity Information
06.06.2011
PIV and PTV in Slug Flow
06.06.2011
Sample Image : Challenges Gas Pocket
Small Bubbles
Tracer particles
Small bubbles in out of focus
Background illumination
Sample Image
Enlarged view
06.06.2011
Uncertainty: Density of tracer particles and bubbles
BIAS RMS
Zarruk et.al (2011)
PIV
PTV
PIV
PTV
Bubble concentration Bubble concentration
06.06.2011
Uncertainty: Slip velocity and angle
06.06.2011
THE LESSON PTV offers better results in multiphase flows
THE PROBLEM PTV data distribution is not uniform. For some statistical analyses, interpolation of data is necessary
06.06.2011
Slug front: Large eddy
o Large eddy observed at
beginning of slug front.
o Ls= 0.6D
o Large eddy: cause for
gas entrainment and
acceleration of stratified
liquid layer
Velocity distribution
06.06.2011
Evolution of liquid phase velocity in slug zone
8 7 6 5 1 3 4 2 9 10 11
5
3 2
7 6
1
8
4
9 10
11
06.06.2011
Costs Operational • Measurement time
Depends on: • Camera characteristics • Frames per second • Image resolution • Inboard camera memory
• Examples: 4GB memory with 1000 fps @ 1024 x1024 pixels = 3 s 4GB memory with 3000 fps @ 512 x 512 pixels = 4 s 4GB memory with 250 fps @ 256 x 256 pixels = 192 s
• Data processing • 24 hours with an optimal processing algorithm • Days – months for large data sets
Financial • State of the art system 2-3 MNOK • Startup system MNOK 0.6
