Planar measurement of three-component velocity by streaked-particle-imaging velocimetry

Abstract

A streaked-particle-imaging-velocimetry (SPIV) technique for the instantaneous planar measurement of three-component velocity has been developed and demonstrated. In this system a camera images the scattered light from two laser sheets onto the same recording medium. One of the laser sheets, double pulsed with short pulse duration, freezes the tracer particle motion and records a pair of images from each tracer. The other laser sheet, cw, provides tracer trajectories whose length is controlled by the sheet thickness. The recorded image from each tracer is then its streak trajectory superimposed on its frozen paired particle image. The planar two components of velocity are deduced from the distance between image pairs and the time separation of the double light pulses. This information, combined with the tracer trajectory streak length, determines the trace particle staying time within the laser sheet. The tracer velocity normal to the laser sheet is then calculated from this staying time and the laser sheet thickness that can be calibrated from the measurements. The resultant SPIV technique was demonstrated with a free jet seeded with small particles, and the derived velocity was reported.