| Whole-field
flow measurement is necessary for determination of velocity and
vorticity vectors for unsteady flows. Particle-image velocimetry (PIV)
provides instantaneous velocity measurement over a planar slice of a
flow field. The IIHR PIV system runs on a dedicated IBM RISC 6000
workstation and utilizes a double- pulsed Nd:YAG laser for generation of
the laser sheet. Image acquisition can be performed either by a CCD
video camera (with 1K x 1 K pixel resolution) or by a still camera with
electronically controlled shutter that is synchronized with laser
pulsing. The velocity vectors are obtained using a digital
auto-correlation technique in which the flow domain is subdivided into a
grid of "interrogation regions" and auto-correlation is
employed within each interrogation region to determine the most like
translation of the particles over the time increment. One velocity
vector measurement is obtained for each interrogation region. A rotating
mirror technique is used to remove directional ambiguity.
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| Researchers examining vortex
flow velocity fields using particle-image velocimetry
instrumentation. |
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| Sample
PIV Data |
A variety of different
PIV systems are employed at IIHR, each of which has advantages depending
on specific applications. The double-pulsed YAG system allows a great
deal of flexibility in specification of the time increment between
images, thus allowing accurate velocity measurement over a wide range of
flow speeds, making the system useful in either water or air flows.
More Information
For more
information about the IIHR double YAG PIV system, please contact Prof.
Jeff Marshall. |
