Nitric-Oxide Planar Laser-Induced Fluorescence Applied to Low-Pressure Hypersonic Flow Fields for the Imaging of Mixture Fraction

The scalar-field imaging of a hypersonic mixing flow is performed in a mixing facility that is shock tunnel driven. The instantaneous mixture-fraction field of a hypersonic two-dimensional mixing layer (M1 = 5.1, M2 = 0.3) is determined with a temperature-insensitive planar laser-induced fluorescence technique with nitric oxide (NO) as the tracer species. Single-shot images are obtained with the broadband excitation of a reduced temperature-sensitivity transition in the A2 (sigma)+ -X2 II1/2 (0, 0) band of NO near 226 nm. The instantaneous mixture-fraction field at a convective Mach number of 2.64 is shown to be nearly identical to a typical diffusive process, supporting the notion of gradient-transport mixing models for highly compressible mixing layers.