Digital image velocimetry

A new technique, digital image velocimetry, is proposed for measurement of instantaneous velocity fields of time dependent flows. A time sequence of single-exposure images of seed particles are captured with a high speed camera, and the sampled images are then digitized on an image processor, enhanced, and superposed to construct a multiple-exposure image. Both the superposed image and a single-exposure image are digitally Fourier transformed for extraction of information on the velocity field. The new technique is designed to improve the flow measurement by eliminating some restrictions of existing optical methods such as laser speckle velocimetry and particle image velocimetry. These restrictions include the limited dynamic range of the velocity measurement, directional ambiguity of the velocity vector, and the difficulty of a real-time capability. The analysis and numerically simulated experiment show that improvement can be achieved with the new technique. Laboratory experiments are currently under investigation.