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| Particle image velocimetry is usually a planar laser light sheet technique in which the light sheet is pulsed twice, and images of fine particles lying in the light sheet are recorded on a video camera or a photograph. The displacement of the particle images is measured in the plane of the image and used to determine the displacement of the particles in the flow. The most common way of measuring displacement is to divide the image plane into small interrogation spots and cross correlate the images from the two time exposures. The spatial displacement that produces the maximum cross-correlation statistically approximates the average displacement of the particles in the interrogation cell. Velocity associated with each interrogation spot is just the displacement divided by the time between the laser pulses. | ||
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If the velocity component perpendicular to the plane is needed, a stereographic system using two lenses can be used. Typically, the PIV measures on a 100 x 100 grid with accuracy between 0.2% and 5% of full scale and spatial resolution ~1mm. But, special design allow for larger and smaller values. Framing rates of most PIV cameras are of order 10Hz, compatible with pulse rates of Nd: Yag lasers, which is too slow for most cinematic recording. Special systems using rapidly pulsed metal vapor lasers and fast cinematic cameras or special high speed video cameras are able to measure up to ~10,000 frames per second. MicroPIV systems have been constructed to measure velocities in cells as small as a few microns. |
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| M. Raffel, C. Willert and J. Kompenhans, Particle Image Velocimetry, a Practical Guide, Springer, Berlin, 1998. | ||
| Grant, editor, Selected Papers on Particle Image Velocimetry, SPIE Milestone Series, MS99, SPIE Optical Engineering Press, Bellingham, Washington, 1994 |
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Dantec Measurement Technology AS | |
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Integrated Design Tools, Inc. | |
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LaVision | |
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Oxford Lasers, Inc. | |
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TSI, Inc. | |
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Spectra Physics | |
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Stanford Research Systems | |
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National Instruments | |
