Nitric-oxide ionization induced Flow Tagging and Imaging for Near-surface Velocimetry in Hypersonic Boundary Layers

In this paper, the authors describe an experimental demonstration of Nitric-oxide ionization induced Flow Tagging and Imaging (NiiFTI) in near-surface velocimetry applications. The flowfield of interest including boundary layers was produced by an Ogive hypersonic model in a Mach 5.7 air flow seeded with 1 % nitric oxide. The diagnostic setup consisted of a 10 Hz nanosecond Nd:YAG-pumped dye laser (1.1 mJ/pulse at 226 nm) and a single intensified camera, making it compatible with conventional NO PLIF. Velocity profiles were collected at two different locations, highlighting the tripped boundary layer growth over distance. Tangential propagation of the laser beam to the model allowed for an effective tagging of the flow beyond 0.1 mm above the surface and mitigation of unwanted interaction of the laser beam and the test article, such as reflections and surface ablation. Flow velocities as low as 30 m/s and as high as 890 m/s were measured inside and outside the boundary layer respectively. Shot-to-shot velocity fluctuations in both regions were also quantified.