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 N ${}_2$ and air gas mixtures are doped with krypton, denoted as 99% N ${}_2$ /1% Kr, and 75% N ${}_2$ /20% O ${}_2$ /5% Kr, respectively. Flow conditions were varied through much of the T5 parameter space (reservoir enthalpy $h_R\approx 5-16$ 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.