Methodology for the application of velocimetry by molecular tagging of hypersonic flows

Abstract

A laser-induced NO fluorescence technique was applied to measure velocity in a hypersonic shock tunnel nozzle exit. For the application of the technique, a detailed study of the density and fluorescence lifetime of the tracer radical, flow velocity and effective test time is proposed, resulting in a methodology for the application of the technique in hypersonic pulsed facilities. The study has demonstrated that it is necessary to jointly evaluate the flow velocity, the fluorescence lifetime of the radical and the width at half height of the laser beam, resulting in a kind of indicator for the feasibility of the technique. The variation of the laser incidence time with respect to the Pitot signal showed that it is not enough to select a stable Pitot pressure signal region to define the laser incidence time, preliminary trial and error analysis are necessary for each device used. Furthermore, the analysis of the velocity values calculated from the linear fit method shows that the adoption of such a method eliminates the effect of the systematic error of the measurements.