A Study of High Speed Flows Using Advanced Optical Diagnostics.

Abstract

Abstract : Over the past few years, we have been working on the development of advanced optical diagnostics to be used in high speed flows. Our focus has been on the techniques based on molecular absorption filters. The focus of this report is on the details of a two-component planar measurement that we call Planar Doppler Velocimetry (PDV) technique. A PDV technique was developed and used to measure two components of instantaneous velocity in an ideally expanded, Mach 2, free jet. The technique utilizes a molecular filter 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 technique were compared with reference LDV measurements taken in the same flowfield. The mean velocity results were in very good agreement with the reference measurements and the turbulence results captured only the correct trend. A detailed error analysis describes the error sources inherent in the PDV technique. For the current two-component PDV system the estimated uncertainty for the mean velocity was better than +/-5%. Methods to improve the technique are discussed.