Improvements and Application of a New Type of Three Component Laser Doppler Velocimeter

摘要

A velocimeter to measure the velocity components in a three dimensional flow field was designed and built. The system uses a set of six monochromatic laser beams converging in the same probe volume, and a single photomultiplier receiving optic. A procedure based on a combination of light frequency shifting, filtering, light chopping, and time sampling, was used to separate the doppler signals corresponding to the various components of velocity. The 45 deg offset forward scattering scheme performs satisfactorily in flow fields with small acceleration such as a jet flow, where in large particles can be used. In larger acceleration flows such as vortex wakes of aircraft and missiles, smaller particles have to be used, and this imposes the adoption of a combined forward scattering scheme.