1. Volumetric 3-Component Velocimetry (V3V)

2. Volumetric 3-Component Velocimetry (V3V)
Individual laser pulses illuminate a volumetric measurement region
3-aperture camera probe captures images of tracer particle locations at each laser pulse, through each imaging aperture
3-dimensional particle positions are calculated based on information from each aperture
Flow velocity is measured based on individual particle displacements in the time between laser pulses

3. V3V Operation 3D3C Imaging Technique Illumination
Based on DDPIV (Gharib – Caltech)
Illumination
Laser illuminates tracers in a volume up to 140 x 140 x 100 mm
2 pulses (like PIV)
3D Camera
3 apertures view measurement region from 3 different perspectives
3D particle locations determined based on information from each aperture
Algorithm
2-Frame Particle Tracking
Velocity is based on individual particle displacements in the time between laser pulses

4. 3D Imaging 3-Aperture Camera
Measurement Volume defined by overlap of 3 viewing angles
Combined information from the 3 apertures yields a particle ‘triplet’ for each particle in the common viewing area.
Measurement
Volume

5. Principle of ‘Triplets’
2 eyes
Focal
Plane
3 apertures
‘Triplet’
Focal
Plane

6. 3D Camera Calibration Automated Multi-plane Calibration
Capture calibration target images in z-planes parallel to the camera.
Find the target center in each plane to correct misalignment error
Find dewarping polynomials in each plane to correct lens distortion
Find pixel adjustment factor in each plane to correct pinhole deviation.
Triplet size at each
calibration plane

7. Validation Part I: Camera Calibration
Camera Calibration is used to correct the discrepancy between a real camera and a perfect camera.
Real Camera
Perfect Camera
Mechanical misalignment error
Optical aberration and distortion
Deviation from pinhole optics (e.g. lens, pixels, aperture locations)
Adjusting reference distance and pixel size
Multi-plane Dewarping

8. Validation Part II: 3D Position Measurement
Grid points on reconstructed calibration targets in multiple z planes

9. V3V Data Processing Right A Left A Top A Right B Left B Top B
TIFF Image
Right A
Left A
Top A
Right B
Left B
Top B
2D Particle Processor
Identify particles in images
P2D File
Right A
Left A
Top A
Right B
Left B
Top B
Triplet Processor
Find particles in 3D space
P3D File
Frame A
Frame B
Velocity Processor
Track particles in 3D space
PV3D/GV3D File
3D Velocity Field

10. 2D Particle Identification Algorithm
2D Gaussian fit of particle image intensity distribution
Using the Levenberg-Marquardt algorithm for non-linear optimization

11. Triplet Search Algorithm
A particle in the top image defines a ray in the left and right images
Algorithm searches along these rays for potential matches
Coarse Search (within 1 pixel)
Fine Search (0.5 pixels)
From: Sharp et al. (2009) Exp in Fluids, in Press.
Calibration planes
Coarse search planes
Fine search planes

12. 3D Particle Tracking 3D particle cloud at t
3D particle cloud at t + Δt
Relaxation Method for Particle Tracking
See for example: Ohmi, Li (2000) Meas. Sci. Tech.
Particles divided into clusters (similar to interrogation region in PIV)
Probability-based matching
From: Sharp et al. (2009) Exp in Fluids, in Press.

13. Velocity on Rectangular Grid
Randomly Spaced Vector Field to Rectangular Grid
Gaussian-weighted Interpolation
(Slice)

14. Example Experimental Setup
Cylinder
3D Camera
Mirror
Laser

15. Data
Flow over a Cube
From: Pan et al. (2007) V3V: A New Tool for 3D Flow Measurement, APS 2007

16. Data Bluegill Fish Wake Vorticity Isosurfaces colored by
Streamwise Velocity
Bluegill Fish Wake
Courtesy: George Lauder, Harvard University

17. Data Vortex Ring from Inclined Exit Re = 2500
From: Troolin, Longmire (2009) Volumetric Velocity Measurements of Vortex Rings from Inclined Exits
Exp in Fluids, In Press.

18. Propeller Measurements
Tip velocity = 3.2 m/s
Courtesy of INSEAN, Italy

19. Mixer with Rushton Turbine
Courtesy of Penn State U

20. Wake flow behind a sphere

21. Measurement of Vortex Ring Impinging on a Plate
1” injector
The second example is the measurement of a vortex ring. Here we uses a 1” injection to push the water into a water tank illuminated by the laser. The vortex ring forms due to the velocity gradient between the center high-speed fluid and the surrounding stagnant fluid. In this figure, the vorticity isosurface clearly shows the shape and size of the vortex ring. The rotation around the vortex ring is also shown by the vector slice. This figure shows the streamlines in the center zone and the rotation zone. We also created two movies that shows the dynamics of the vortex ring flow.

22. Vortex Ring Impinging on a Plate

23. Vortex Ring Impinging on a Plate

24. Vortex Ring Impinging on a Plate

25. Vortex Ring Impinging on a Plate