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Volumetric 3-Component Velocimetry (V3V)

Volumetric 3-Component Velocimetry (V3V). 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.

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Volumetric 3-Component Velocimetry (V3V)

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

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

  9. V3V Data Processing Right A Right B Right B Right A Top B Top A Top B Top A Left A Left B Left B Left A TIFF Image 2D Particle Processor Identify particles in images P2D File 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 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

  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

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