General-Purpose Stereo Imaging Velocimetry

John H. Glenn Research Center, Cleveland, Ohio

An improved and expanded method of stereo imaging velocimetry (SIV) for diagnosing three-dimensional flows of gases, liquids, and other fluids involves the use of standard charge-coupled-device cameras positioned orthogonally to each other. In addition to providing a full-field, quantitative, three-dimensional map of any optically transparent flow seeded with tracer particles, this SIV method incorporates a camera-calibration technique, in which rotation and translation of camera lenses and optical distortion generated in the lenses are taken into account by use of an accurate two-dimensional-to-three-dimensional mapping function.

Three-Dimensional Particle Tracking is a major element of the present improved SIV method.

Other improvements over the basic SIV method incorporated into the present method include the following:

An additional image-reconstruction technique accounts for severe distortion in order to enable the reconstruction of incomplete calibration images so that there is less loss of the field of view than there would be in the absence of this technique.
A new technique for extracting images of tracer particles involves nonattenuating subtraction of image background coupled with a nonattenuating threshold alternative that yields a significant improvement over previous techniques.
Previously, particles were tracked in two dimensions in each view and then the tracks were matched to produce approximate three-dimensional vectors. A new technique for tracking particles in three dimensions provides true three-dimensional velocity vectors from two orthogonal views or from any set of three-dimensional data. This is a significant advancement in SIV.
Color image processing has been added, making it possible to analyze flows of multiphase fluids, thereby expanding capabilities and applications beyond those of SIV as practiced heretofore.

While there is a patent on SIV (U.S. Patent 5,905,568), the present method goes beyond the patent, making possible experiments that were previously impossible. In particular, true three-dimensional particle tracking has not been done in SIV until now. The present method makes it possible to perform quantitative, three-dimensional, full-field analyses of flow fields in any fluids that can be seeded with tracer particles.

This work was done by Mark McDowell of Glenn Research Center.

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