Freestream Multi-species and Near-body Atomic Oxygen Measurements in the T5 Shock Tunnel by Tunable Diode Laser Absorption Spectroscopy

We deploy a suite of laser-based sensors to instrument hypervelocity gas flows in the T5 Free-Piston Reflected Shock Tunnel. The six employed infrared lasers rely on Tunable Diode Laser Absorption Spectroscopy (TDLAS) to measure temperature and concentration of nitric oxide, carbon monoxide, carbon dioxide, and water in the Mach 5 freestream, and to detect electronically-excited atomic nitrogen and oxygen behind a Mach stem generated by a symmetric, opposing pair of wedge models. Hypervelocity computational fluid dynamics (CFD) modeling of the wedge models, completed in US3D, inform beam position selection for the atomic nitrogenand oxygen-targeting TDLAS sensors relative to the opposing wedge models, and limited comparisons between experiments and these planning-phase simulations are conducted. This work encompasses two separate experiments in T5, both conducted at the same 16 MJ/kg nominal condition. The freestream sensors collect independent measurements of rotational and vibrational temperatures but find the test gas to be in thermal equilibrium, in general agreement with previous TDLAS-based measurements in the T5 freestream at this condition. The Mach-stem sensors detect electronically excited states of atomic nitrogen and oxygen at parts-per-billion concentrations. We detect the targeted atomic oxygen state during the test time, but atomic nitrogen is only measurable during the unsteady facility startup process. Measurements in both regions are made at 50 kHz. Because electronically excited atomic species are important experimental targets for developing hypervelocity CFD, these measurements demonstrate the capability of TDLAS data to contribute to improving hypervelocity models.