An extension of digital PIV-processing to double-exposed images |
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Authors: | H Huang |
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Institution: | (1) Graduate Aeronautical Laboratories of California Institute of Technology, Pasadena, CA 91125, USA, US |
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Abstract: | In this paper digital processing techniques for PIV (Partical Image Velocimetry) using double-exposed particle images have
been studied. It has been found that a pattern matching technique is significantly superior to the traditional autocorrelation
method in the case that a large particle displacement between the double exposures is present on the image. In PIV using double-exposed
images, the image shifting technique is usually used to solve the directional ambiguity problem. The performance of PIV using
autocorrelation technique is dependent on the flow speed and the amount of image shift applied. This dependence, for example,
causes a difficulty of autocorrelation in flows close to a solid boundary. The present study shows that a pattern matching
technique eliminates such a difficulty. At the same signal-to-noise ratio, the pattern matching techndique has a better spatial
resolution than that of autocorrelation. In concert with the pattern matching technique, PID (Particle Image Distortion) can
be applied to double-exposed images, further improving the reliability and accuracy of velocity estimates of PIV in the presence
of large velocity gradients. Generally speaking, PIP-matching and PID extend the validity of PIV using double-exposed images.
The total processing time required by the PIV using the pattern matching technique and one PID iteration is of the same order
as that required by the PIV using autocorrelation.
Received: 7 July 1995 / Accepted: 11 September 1997 |
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