Evaluation of nitric oxide laser-induced fluorescence thermometry techniques in a hypersonic boundary layer

Nitric oxide planar laser-induced fluorescence was performed to measure the wall-normal distribution of static temperature through a hypersonic boundary layer. A 10-degree half-angle wedge model was oriented at a 5-degree angle of attack in the NASA Langley 31-in Mach 10 facility, resulting in a 5-degree flow turning angle and an edge Mach number of 7.6. Nitric oxide was seeded through a spanwise slot into the boundary layer upstream of the imaging region and was excited with a pulsed ultraviolet planar laser sheet. The laser was spectrally scanned across six fluorescence transitions in the (0, 0) band of the $$A^2\Sigma ^+$$–$$X^2 \Pi $$ system. Eighteen thermometry methods were assessed through comparison to predictions of the temperature field from computational fluid dynamics simulations. The effect of spectral resolution and laser linewidth on measurement uncertainty was also investigated. The most accurate technique was spectral peak thermometry, which achieved an accuracy of ± 31.6 K ($$12.6\%$$ error relative to CFD temperature). The spectral peak thermometry technique required a minimum spectral resolution between 0.074 and 0.102 $$ {\mathrm {cm}}^{-1} $$ and a maximum laser linewidth of 0.49 $$ {\mathrm {cm}}^{-1} $$ to extract meaningful temperature information from the spectra.