Flow-Tagging Velocimetry for Hypersonic Flows Using Fluorescence of Nitric Oxide

We demonstrate a new variation of molecular-tagging velocimetry for hypersonic e ows based on laser-induced e uorescence. A thin line of nitric-oxide molecules is excited with a laser beam and then, after a time delay, a e uorescence image of the displaced line is acquired. One component of velocity is determined from the time of e ight.Thismethodisappliedtomeasurethevelocityproe leinaMach8.5laminar,hypersonicboundarylayerinthe Australian National University’ s T2 free-piston shock tunnel. The single-shot velocity measurement uncertainty in the freestream was found to be 3.5%, based on 90% cone dence. The method is also demonstrated in the separated e ow region forward of a blunt e n attached to a e at plate in a Mach 7.4 e ow produced by the Australian National University’ s T3 free-piston shock tunnel. The measurement uncertainty in the blunt e n experiment is approximately 30%, owing mainly to low e uorescence intensities, which could be improved signie cantly in future experiments. This velocimetry method is applicableto very high-speed e ows that have low collisional quenching of the e uorescing species. It is particularly convenient in facilities where planar laser-induced e uorescence is already being performed.