The development of a Laser-Doppler velocity meter for the measurement of solid particle velocity in a two-phase flow

Report (1972)
Copyright: © 1972 Von Karman Institute for Fluid Dynamics
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Published Date

01-10-1972

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VKI Training Center for Experimental Aerodynamics Technical Note 81

Abstract

A laser-doppler "fringe" velocity meter was developed with the use of simple optical equipment and low laser power (less than 1 milliwatt), for the measurement of the velocity of solid particles (diameter up to 500 microns) in a two-phase flow. The potential for a higher signal-to-noise ratio and the ease of alignment made the fringe technique more appealing than other laser-doppler methods for the present application of velocity measurements between zero and 20 meters per second. A rotating simulation wheel was used during the development which used small wires of 100 to 500 microns in diameter to provide a most satisfactory representation of the actual particle and fringe pattern interaction. The present system gave doppler signals of extremely good quality with accurate velocity readings. The results demonstrated the successful use of a fringe laser-doppler system to measure the velocity of particles of a size much greater than the average fringe spacing. For a fringe separation of about 35 microns, successful velocity measurements of 100 and 500 micron spherical glass particles in a gas nozzle flow were made. The present system may ea6ily be extended to a much larger velocity range by utilizing the full power of the 1 milliwatt He-Ne laser.