AAE 520 Experimental Aerodynamics
Particle Image Velocimeter
Purdue University - School of Aeronautics and Astronautics
AAE 520 Experimental Aerodynamics
Why use imaging?
Conventional methods
(HWA, LDV)
•
•
•
•
Single-point measurement
Traversing of flow domain
Particle image velocimetry
•
•
•
Whole-field method
Non-intrusive (seeding)
Instantaneous flow field
Time consuming
Only turbulence statistics
z
After: A.K. Prasad, Lect. Notes short-course on PIV, JMBC 1997
Purdue University - School of Aeronautics and Astronautics
AAE 520 Experimental Aerodynamics
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).
Purdue University - School of Aeronautics and Astronautics
AAE 520 Experimental Aerodynamics
PIV optical configuration
Multiple Flashes
Of Light
Laser
Sheet
Purdue University - School of Aeronautics and Astronautics
AAE 520 Experimental Aerodynamics
Multiple-exposure PIV image
Purdue University - School of Aeronautics and Astronautics
AAE 520 Experimental Aerodynamics
Velocity from tracer motion
Prob(detect) ~ image density (NI)
Low image density
NI << 1
Particle tracking velocimetry
High image density
NI >> 1
Particle image velocimetry
Purdue University - School of Aeronautics and Astronautics
AAE 520 Experimental Aerodynamics
PIV Interrogation analysis
RP
RD-
RD+
RC+RF
Double-exposure
image
Interrogation
region
Spatial
correlation
Purdue University - School of Aeronautics and Astronautics
AAE 520 Experimental Aerodynamics
PIV result
Turbulent pipe flow
Re = 5300
100×85 vectors
“Hairpin” vortex
Purdue University - School of Aeronautics and Astronautics
AAE 520 Experimental Aerodynamics
Visualization vs. Measurement
Purdue University - School of Aeronautics and Astronautics
AAE 520 Experimental Aerodynamics
Inherent assumptions
• Tracer particles follow the fluid motion
• Tracer particles are distributed homogeneously
• Uniform displacement within interrogation
region
Purdue University - School of Aeronautics and Astronautics
AAE 520 Experimental Aerodynamics
“Ingredients”
FLOW
sampling
seeding
quantization
illumination
enhancement
Acquisition
Pixelization
imaging
registration
selection
correlation
Interrogation
estimation
RESULT
analysis
validation
Purdue University - School of Aeronautics and Astronautics