Molecular Tagging Using Vibrationally Excited Nitric Oxide in an Underexpanded Jet Flowfield

We report a laser diagnostic technique which relies on planar laser-induced fluorescence of vibrationally excited nitric oxide (NOv 1) molecules produced from the 355 nm photodissociation of seeded NO2 for molecular tagging velocimetry applications. The technique was applied toward an axisymmetric highly underexpanded jet flowfield to yield single-component (streamwise) velocity maps. Detection of the photodissociated NOv 1 molecules would be valuable in flow environments where molecular tagging velocimetry would be highly desirable, but where there are also significant background concentrations of NO. The technique would also be valuable in high-quenching and/or low-velocity flow conditions due to the long-lived nature of the photodissociated NO molecules. Single-shot streamwise velocity uncertainties were about 5% and could be lowered by increasing signal to noise. In addition, the vibrational relaxation of NO was explored in support of a U.S. Air Force Office of Scientific Research Multidisciplinary University Research Initiative project and it was found that the vibrational decay of NO was heavily dependent on collisional vibrational relaxation with oxygen atom formed through NO2 photodissociation.