Application of a Laser-doppler Technique to the Measurement of Particle Velocity in Gas-particle Two-phase Flow

In chemical propulsion, the use of metallic fuel constituents burning to particulate refractory oxides in rocket engines has forced attention to the understanding of two-phase nozzle expansion processes. In this study light from a helium-neon laser was reflected both from a fixed target and from moving particles. A lens concentrated the laser light and the light back-scattered from the particles was picked up by the same lens and directed into a Fabry-Perot scanning plate interferometer. The interferometer limited observation at any moment to those particles whose Doppler shifted frequency coincided with the interferometer transmission frequency. The light from the fixed target provided a frequency reference system, and calibrated movement of the interferometer mirror spacing provided continuous examination of velocity. Data in the form of lightscattering and number count vs velocity has been obtained for water droplets in subsonic flow, for aluminum spheres and alumina abrasive in cold supersonic flow and for aluminum and magnesium oxide in hot supersonic flow. Number count-velocity data was found to be a complicated function of particle size distribution and vector velocity distribution as well as instrument characteristics.