Particle tracking velocimetry

Particle tracking velocimetry (PTV) is one of velocimetry methods, i.e a technique to measure velocity of particles. The name suggests that the particles are tracked, and not only recorded as an image as it is suggested in another form, particle image velocimetry. There are two very different experimental methods:

• the two dimensional (2D) modification of Particle Image Velocimetry (PIV), in which the flow field is measured in the two-dimensional slice of the flow, illuminated by a laser sheet (a thin plane) and low density of seeded particles allow for the tracking each of them individually for several frames.
• the Three-Dimensional Particle tracking velocimetry (3D-PTV) is a distinctive experimental technique, based on multiple camera-system, three-dimensional volume illumination and tracking of flow tracers (i.e. particles) in three-dimensional space by using photogrammetric principles.

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Description

A typical installation of the 3D-Particle tracking velocimetry consists of three or four digital cameras, installed in an angular configuration, synchroniously recording the diffracted or fluorescent light from the flow tracers, seeded in the flow. The flow is illuminated by a collimated laser beam, or by another source of light. There is no restriction on the light to be coherent or monochromatic and only its illuminance has to be sufficient to illuminate the observational volume. Particles or tracers could be fluorescent, diffractive, tracked through as many as possible consecutive frames on as many cameras as possible. In principle, two cameras in the stereoscopic configuration are sufficient in order to determine the three coordinates of a particle in space, but in most practical situations, three or four cameras are necessary.

3D-PTV schemes

Example of 3D-PTV facility, with 4 CCD cameras and the laser illumination from the bottom of a glass tank. In courtesy of J. Willneff, ETH Zurich. [1]

See also

• Particle image velocimetry
• Laser Doppler velocimetry
• Hot-wire anemometry
• Molecular tagging velocimetry

References

• Maas, H.-G., 1992. Digitale Photogrammetrie in der dreidimensionalen Strömungsmesstechnik, ETH Zürich Dissertation Nr. 9665
• Malik, N., Dracos, T., Papantoniou, D., 1993. Particle Tracking in threedimensional turbulent flows - Part II: Particle tracking. Experiments in Fluids Vol. 15, pp. 279-294
• Maas, H.-G., Grün, A., Papantoniou, D., 1993. Particle Tracking in threedimensional turbulent flows - Part I: Photogrammetric determination of particle coordinates. Experiments in Fluids Vol. 15, pp. 133-146
• Lüthi, B., Tsinober, A., Kinzelbach W. (2005)- Lagrangian Measurement of Vorticity Dynamics in Turbulent Flow. Journal of Fluid Mechanics. (528), p. 87-118
• Nicholas T. Ouellette, Haitao Xu, Eberhard Bodenschatz, A quantitative study of three-dimensional Lagrangian particle tracking algorithms, Experiments in Fluids, Volume 40, Issue 2, Feb 2006, Pages 301 - 313.