Particle Image Velocimeter

1
Particle Image Velocimeter
2
Why use imaging?

• Conventional methods
• (HWA, LDV)
• Single-point measurement
• Traversing of flow domain
• Time consuming
• Only turbulence statistics

• Particle image velocimetry
• Whole-field method
• Non-intrusive (seeding)
• Instantaneous flow field

After A.K. Prasad, Lect. Notes short-course on
PIV, JMBC 1997
3
Coherent structures in a TBL
Kim, H.T., Kline, S.J. Reynolds, W.C. J. Fluid
Mech. 50 (1971) 133-160.
Smith, C.R. (1984) A synthesized model of the
near-wall behaviour in turbulent boundary
layers. In Proc. 8th Symp. on Turbulence
(eds. G.K. Patterson J.L. Zakin) University of
Missouri (Rolla).
4
PIV optical configuration
Multiple Flashes Of Light
Laser Sheet
5
Multiple-exposure PIV image
6
Velocity from tracer motion
Prob(detect) image density (NI)
Low image density
NI ltlt 1
Particle tracking velocimetry
High image density
NI gtgt 1
Particle image velocimetry
7
PIV Interrogation analysis
RP
RD
RD-
RCRF
Double-exposure image
Spatial correlation
Interrogation region
8
PIV result
Turbulent pipe flow Re 5300 10085 vectors
Hairpin vortex
9
Visualization vs. Measurement
10
Inherent assumptions

• Tracer particles follow the fluid motion
• Tracer particles are distributed homogeneously
• Uniform displacement within interrogation region

11
Ingredients
FLOW
sampling
seeding
quantization
Pixelization
illumination
enhancement
Acquisition
imaging
selection
registration
correlation
Interrogation
estimation
RESULT
validation
analysis