|Digital Particle Image
Digital Particle Image Velocimetry (DPIV) is a planar optical measurement technique which provides a means of measuring the velocity of seeded particles (~1 - 50 microns (in air)) in the flow of interest over a plane using a charge-coupled device (CCD) camera. The measurement area within the flow field is defined by the position and physical dimension of a fan of laser light. With the illumination of two short duration laser flashes in the measurement area, a double-exposure of the flow field is captured (through the CCD camera to the frame grabber card) on the computer. Once the spatially displaced images are stored in two separate frames, each velocity vector is extracted by performing mathematical correlation analysis on a cluster of particles within each interrogation region between the two frames (eliminating the problem of directional ambiguity). The PIV interrogation process is repeated until all the required velocity information is extracted from the captured record. There should be a high enough seeding concentration of particle images within the interrogation window to minimise any potential bias error arise from data drop out (See Westerweel 2000).
In general terms, particle image velocimetry (PIV) is the low particle concentration equivalent of Laser Speckle Velocimetry (LSV) and developed from speckle interferometry which is used to measure surface displacements in solid mechanics.
However, unknown to the PIV community, as early as in 1971, a paper published in a journal entitled "An Automated Technique for Obtaining Cloud Motion from Geosynchronous Satellite Data Using Cross Correlation" by J.A. Leese et al. Journal of Applied Meteorology Vol. 10. pp.118-132, had clearly demonstrated the validity of cross-correlation techniques as a whole flow field motion tracker in a massive scale!
DPIV is now regarded by many as the method of choice in measuring velocity data for code validation in
Computational Fluid Dynamics (CFD). The
information generated is what we would call Quantitative Flow
PIV) can be extended to
measure the out-of-plane velocity component with an additional camera, frame grabber and some optics that use
Current trend has shown that there
is a need to develop Micro-PIV for applications in micro-channel flows and
A conceptually simple and mature planar (near instantaneous) flow measurement technology. DPIV will in the future become the standard in fluid flow measurements within industrial sectors (e.g. car manufacturers) and universities all over the world.