Photon Doppler velocimetry measurements of transverse surface velocities

Abstract

An experiment consisting of a 30-mm diameter aluminum disk mounted to an electric rotary tool was utilized to develop a technique for measuring transverse velocity using Photon Doppler Velocimetry (PDV). A single fiber optic collimator was positioned along the rotational axis of the wheel, at various angles, to resolve the apparent transverse velocity. Different surface preparations were explored to achieve near retroreflective light return, such as: polished, retroreflective microspheres, milled v-cuts, and electrochemical etching. To characterize these surfaces, light return and velocities were recorded for each surface preparation as a function of angle. Measurements were performed over a range of 0 to 51 degrees from the surface normal for each preparation. Polished and electrochemically etched surfaces did not provide enough reflected light to resolve a beat frequency, however, retroreflective microspheres and milled v-cuts provided adequate reflected light up to 51 degrees. Transverse velocity components were resolved using both retroreflective microspheres and milled v-cuts in the spinning wheel experiment. Application of the two surface preparations were then studied in gas gun experiments. Retroreflective microspheres were studied in a planar impact experiment, and mechanical milling was studied in an oblique impact experiment. A normal and transverse profile of particle velocity was resolved in the oblique impact experiment.