Freestream velocity-profile measurement in a large-scale, high-enthalpy reflected-shock tunnel

Abstract: We apply Krypton Tagging Velocimetry (KTV) to measure velocity profiles in the freestream of a large, national-scale high-enthalpy facility, the T5 Reflected-Shock Tunnel at Caltech. The KTV scheme utilizes two-photon excitation at 216.67 nm with a pulsed dye laser, followed by re-excitation at 769.45 nm with a continuous laser diode. Results from a nine-shot experimental campaign are presented where N₂ and air gas mixtures are doped with krypton, denoted as 99% N₂/1% Kr, and 75% N₂/20% O₂/5% Kr, respectively. Flow conditions were varied through much of the T5 parameter space (reservoir enthalpy h_R≈ 5 - 16 MJ/kg). We compare our experimental freestream velocity-profile measurements to reacting, Navier–Stokes nozzle calculations with success, to within the uncertainty of the experiment. Then, we discuss some of the limitations of the present measurement technique, including quenching effects and flow luminosity; and, we present an uncertainty estimate in the freestream velocity computations that arise from the experimentally derived inputs to the code. Graphic Abstract: [Figure not available: see fulltext.]