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

Abstract

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 . 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 but over less than 10% of the core flow for specific bulk enthalpies above about . Axial velocimetry was performed using molecular tagging velocimetry. Axial velocities of about 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 were measured.