Two-Component Planar Doppler Velocimetry in High Speed Flows

Abstract

A planar Doppler velocimetry technique was developed and used to measure two components of instantaneous velocity in an ideally expanded, Mach 2, freejet. The technique utilizes a molecular e lter as a frequency discriminator and uses two cameras to resolve two components of velocity on a plane that is illuminated by a laser sheet. Careful formation of the laser sheet, proper calibration of the splitter/recombiner imaging system, and precise image registration were found to be critical steps in the technique. The velocity measurements obtained with this techniquewerecompared with referencelaser Dopplervelocimetry measurementstaken in thesame e owe eld. The mean velocity results were in very good agreement with the reference measurements, and the turbulence results captured the correct trend but were higher than thereference results. A detailed error analysis describes the error sources inherent in the planar Doppler velocimetry technique. For the current two-component planar Doppler velocimetry system, theestimated uncertainty forthe xandy componentsofvelocity were §5and §3:5%ofthejet centerline velocity, respectively. The errors in the x component of velocity were within the estimated uncertainty. The errors in the y component of velocity exceeded the estimated uncertainty. Possible causes for this difference are discussed.