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Imaging Techniques for Flow and Motion Measurement
Lecture 3
Lichuan Gui
University of Mississippi
2011
Particle Image Velocimetry (PIV) Particle Image Velocimetry (PIV)
IntroductionIntroduction
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Particle Image Velocimetry (PIV)Particle Image Velocimetry (PIV)
• Optical, non- or minimally-intrusive, fluid flow measurement technique;
• Instantaneous flow measurements in two-dimensional (2D) area or three-dimensional (3D) volume field of views;
• Basic procedure of PIV– Flow visualization
• Flow field seeded with small tracer particles• Particles usually illuminated by a laser light sheet
– Image recording• Particle images captured by an imaging system
– Image evaluation• Usually using auto- or cross-correlation algorithm
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Stroboscopic illumination techniques
Flow visualization with small particlesFlow visualization with small particles
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Oil drop in laminar pipe flow (Air) Solid particles in water flow
Multiple exposed particle images
Flow visualization with small particlesFlow visualization with small particles
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2D & 2-component PIV Systems2D & 2-component PIV Systems
CW laser with high-speed photo or video camera
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Fluorescent particles in a microdevice0.540.41 mm2, 30 fps
Smoke flow in air0.50.5 mm2, 500 fps
Consecutive singly exposed PIV recordings
2D & 2-component PIV Systems2D & 2-component PIV Systems
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Measurement volumeLaser
Lenst=t0
Light sheet
Lens system & Camera
Fluid flow seeded with small tracer particles
Double exposed recording
Exposure #1
t=t0
Image #1
Single exposed recording
Standard 2D PIV
2D & 2-component PIV Systems2D & 2-component PIV Systems
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Measurement volume
Lens
t=t0
t=t0+t
Lens system & Camera
Light sheet
Single exposed recording Double exposed recording
Fluid flow seeded with small tracer particles
Image #1
t=t0+t
Image #2
Exposure #1Exposure #2
Laser
Standard 2D PIV
2D & 2-component PIV Systems2D & 2-component PIV Systems
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Image plane
Objective Lens
Laser light sheet
Laser light sheet
Image plane
Objective Lens
S
S’
L
L’
Scale factor: M=L/L’
Time interval: t
Velocity: V=S/t=M·S’/ t
Velocity determination with standard 2D PIV
2D & 2-component PIV Systems2D & 2-component PIV Systems
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Flood Illumination
=532 nm
= 610 nm
Nd:YAG LASERNd:YAG LASER
MICROSCOPEMICROSCOPE
BEAM EXPANDERBEAM EXPANDER
CCD CAMERACCD CAMERA
MCROFLUIDIC DEVICEMCROFLUIDIC DEVICE
Nd:YAG Laser
Micro Device
Flow in Flow out
Glasscover
CCD Camera(1280x1024 pixels)
BeamExpander
Epi-fluorescentPrism / Filter Cube
Microscope
Focal Plane
Micro-PIV image pair
Micro-Fluidics LabPurdue University
Micro-scale PIV (MPIV) SystemMicro-scale PIV (MPIV) System
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– Stereo PIV• 3 velocity components in a plane• Two cameras
– Holographic PIV• 3 velocity components in a 3 dimensional volume• Complex and precise illumination
– Defocusing PIV (Pereira et al. 2000)• Allow images to become defocused• Single camera/ color CCD, particle image tracking
– Multiple-sheet PIV (Raffel et al.,1995 ) • Multiple laser light sheet, single camera
– 3D scanning PIV (Brücker, 1997) • Scanning a 3D volume with a laser beam • Single high speed camera
3D or 3-component PIV Systems3D or 3-component PIV Systems
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Stereo PIV configurationsa. Translation systems (lateral displacement)b. Rotational systems (angular displacement)
Scheimpflug condition
3D or 3-component PIV Systems3D or 3-component PIV Systems
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Stereo PIV data reduction
- Translation systems (Mn=di/do)
3D or 3-component PIV Systems3D or 3-component PIV Systems
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Stereo PIV data reduction
- Rotational system (Mnconstant)
3D or 3-component PIV Systems3D or 3-component PIV Systems
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Holographic PIV (HPIV) SystemHolographic PIV (HPIV) System
Holographic diagnostics of a 3D particle filed
a. Hologram recordingb. Hologram reconstruction
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Holographic PIV (HPIV) SystemHolographic PIV (HPIV) System
Holographic recording of particles
Interference pattern in a HPIV recording
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Holographic PIV (HPIV) SystemHolographic PIV (HPIV) System
Reconstructed HPIV particle images
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Holographic PIV (HPIV) SystemHolographic PIV (HPIV) System
Example of HPIV system (recording)
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Holographic PIV (HPIV) SystemHolographic PIV (HPIV) System
Example of HPIV system (reconstruction)
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Practice with EDPIV software
1. Read EDPIV help manual page to know details in “Raw Image Format” window
2. Open images in application example #0 with EDPIV and look at image details.
EDPIV software and sample images are available at http://www.edpiv.com/
HomeworkHomework
