Optical Sensors Group

This paper describes a planar Doppler velocimetry (PDV) technique that is capable of measuring the three, instantaneous and time average components of velocity over two dimensions using a single pair of signal and reference cameras. PDV can be used to measure the instantaneous 3-D velocity of a fluid by using an absorption line filter to determine the Doppler shifted frequency of a narrow line-width, pulsed laser that has been scattered from particles seeded into the flow. In the technique presented here the three views required to obtain three component velocity information are guided from the collection optics to a single imaging plane using flexible fiber imaging bundles. These are made up of a coherent array of single fibers and are combined at one end as the input plane to the measurement head. A fourth leg of the imaging fiber bundle is used to image the individual laser pulses and allow correction for pulse-to-pulse frequency variations. As part of the development phase of the technique measurements are presented of the velocity field of a rotating disk using both an Argon Ion laser giving time average results and a frequency doubled Nd:YAG laser to give an instantaneous result. A typical vector map of the computed velocity is shown in Figure 1. In this figure vectors are shown at only 1 in 10 data points. X [mm]