Velocity Profile Measurements in Hypersonic Flows Using Sequentially Imaged Fluorescence-Based Molecular Tagging

Nitric-oxide planar laser-induced fluorescence was used to perform velocity measurements in hypersonic flows by generating multiple tagged lines that fluoresce as they convert downstream. Determination of axial velocity was made by application of a cross-correlation analysis of the horizontal shift of individual tagged lines. A single interline, progressive scan-intensified charge-coupled device camera was used to obtain two sequential images of the nitric-oxide molecules that had been tagged by the laser. The charge-coupled device allowed for submicrosecond acquisition of both images, resulting in submicrosecond temporal resolution as well as submillimeter spatial resolution (0.5 mm horizontal, 0.7 mm vertical). Quantification of systematic errors, the contribution of gating/ exposure duration errors, and the influence of collision rate on temporal uncertainty were made. This velocity measurement technique has been demonstrated for two hypersonic flow experiments: 1) a reaction control system jet on an Orion crew exploration vehicle wind-tunnel model and 2) a 10 deg half-angle wedge with a 2-mm-tall 4-mm-wide cylindrical boundary-layer trip. Mean-velocity uncertainties below 30 m/s (2.7% of the measured average velocity) and single-shot uncertainties below 100 m/s (9.7% of the measured average velocity) have been obtained in regions with optimal signal intensities using this technique.