Nitric-Oxide Planar Laser-Induced Fluorescence Measurements in the Hypersonic Materials Environmental Test System

摘要

Planar laser-induced fluorescence of naturally occurring nitric oxide has been used to provide insight into baseline flow conditions of the Hypersonic Materials Environmental Test System 400 kW arc-heated wind tunnel at NASA Langley Research Center via radial and axial velocity measurements and instantaneous flow-visualization images. This represents both the first flow-tagging velocity measurements and the first application of nitric-oxide planar laser-induced fluorescence flow visualization in an arcjet facility. Results are presented at selected facility run conditions, including some in a simulated Earth atmosphere (75% nitrogen, 20% oxygen, 5% argon) and others in a simulated Martian atmosphere (71 % carbon dioxide, 24 % nitrogen, 5 % argon) for specific bulk enthalpies ranging from 6.5 to 18.4 MJ/kg. Flow-visualization images reveal the presence of large-scale unsteady flow structures and indicate nitric-oxide fluorescence signal over more than 70% of the core flow for specific bulk enthalpies below about 11 MJ/kg but over less than 10% of the core flow for specific bulk enthalpies above about 16 MJ/kg. Axial velocimetry was performed using molecular tagging velocimetry. Axial velocities of about 3 km/s were measured along the centerline. Radial velocimetry was performed by scanning the wavelength of the narrowband laser and analyzing the resulting Doppler shift. Radial velocities of ±0.5 km/s were measured.