Flow Measurement by Laser Speckle Photography

Abstract

This paper describes the results of the application of Laser Speckle Photography to flow measurement. Before flow field measurement, LSP is applied to measure the speed of rotating disk. The specklegram (double-exposured film) obtained by pulsed ruby laser gives Young's fringes which represents the speed and moving direction. The characteristics of laser speckle itself, particularly its size, contrast of the speckle pattern and so on, are examined here for obtaining the clear specklegram. It is found in this case that a high power (about 1J/pulse) pulsed laser must need for flow measurement. The so-called PIV (Partille Imaging Velocimetry), using quasi-specklegram by seeding particles, is of useful technique for practical measurements. The high sensitivity film can be used in this case.