Measurement of displacement in spatial correlation velocimetry by pixel shifting method

Abstract

Displacement of small granular particles during the flow process has been measured by laser speckle correlation with counting of pixel shifting technique. Speckle pattern velocimetry provides instant velocity measurements in a fluid flow. Micron size particles are seeded in the stream, which scatters laser light. With the help of cylindrical lens, a laser sheet designed to illuminate the particles in the measurement plane. CCD is placed perpendicular to the laser sheet to acquire sequential images of the illuminated flow field. The second image is recorded a short time later during which the seeds will have relocated due to the flow. The image pair develops a field of linear displacement vectors. This effort sorts out the ambiguity in direction of displacement by cross correlation. The displacement and velocity measurements are estimated by a novel counting of pixel shifting calculation method.