Stereo Imaging Velocimetry

In its proposed configuration, the NASA Lewis Research Center's Stereo Imaging Velocimeter will consist of at least two charged coupled device (CCD) cameras, oriented at some relative angle with respect to each other. The cameras will observe a fluid experiment that has been seeded with tracer particles that are neutrally buoyant to permit accurate flow tracking. Except for the tracer particles, this measurement technique will be nonintrusive. Velocity accuracies will be on the order of 1 to 5 percent of full field. Each camera will make a two-dimensional record of the motion of the seed particles in the observation volume. Three-dimensional data will be obtained by computationally combining the two-dimensional information.

Left: Fluid experiment seeded with tracer particles. Right: SIV three-dimensional velocity vectors.

Stereo imaging velocimetry subdivides into several problems:

• Camera calibration
• Centroid determination with overlap decomposition
• Particle tracking
• Stereo matching
• User interface
• Testing and error analysis

Benefits

• Stereo imaging velocimetry provides a diagnostic tool for quantitative and qualitative characterization of fluid flows.
• Stereo imaging velocimetry permits direct comparison between computed and experimentally measured three-dimensional flows.
• A PC-based stereo imaging velocimetry applications package is available for incorporation into fluid experiments.

Technology Transfer Highlight

Continuous casting model showing raw vectors (left) and SIV vectors (right).

SIV will give LTV advantages over previous qualitative analyses of mold flow (dye injection and video taping). It will provide vector maps of the mold flow which show the direction and magnitude of the flow; these parameters have never been seen with dye injection. In addition, SIV-generated flow-field data will provide more data points for verification and for mathematical models.

Find out more about SIV.