High-speed planar laser-induced fluorescence investigation of nitric oxide generated by hypersonic Mach reflections for computational fluid dynamics validation

In this article, the authors present an experimental investigation of thermochemical relaxation regions downstream symmetric Mach reflections generated in 8.5 flows with stagnation enthalpies from 7 to 10 MJ/kg. The experiment was performed Hypervelocity Expansion Tunnel at National Aerothermochemistry and Hypersonics Laboratory Texas A&M University. focused on studying nitric oxide morphology vicinity a strong normal shock wave shear layers. Experimental planar laser-induced fluorescence measurements 250 kHz repetition rate quasi-simultaneous natural emission photography demonstrate sufficient rejection reveal intricate flow structures vicinity. Steady computational fluid dynamics (CFD) solutions obtained US3D software were used simulate signal levels for quantitative comparison against experimentally acquired data. accomplished four objectives: complex flowfield visualization stem 4 μs temporal resolution, evaluation level high-temperature chemistry effects introduced freestream by expansion tunnel, both qualitative CFD simulation validation, cross-checking or introduction fundamental properties including absorption cross section vibrationally excited states collisional quenching atomic nitrogen.