Nitric Oxide PLIF Measurements in the Hypersonic Materials Environmental Test System (HYMETS)

Abstract

A nonintrusive laser-based measurement system has been applied for the first time in the HYMETS (Hypersonic Materials Environmental Test System) 400 kW arc-heated wind tunnel at NASA Langley Research Center. Planar laser-induced fluorescence of naturally occurring nitric oxide (NO) has been used to obtain instantaneous flow visualization images, and to make both radial and axial velocity measurements. Results are presented at selected facility run conditions, including some in simulated Earth atmosphere (75% nitrogen, 20% oxygen, 5% argon) and others in simulated Martian atmosphere (71% carbon dioxide, 24% nitrogen, 5% argon), for bulk enthalpies ranging from 6.5 MJ/kg 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 bulk enthalpies below about 11 MJ/kg, but over less than 10% of the core flow for bulk enthalpies above about 16 MJ/kg. Axial velocimetry was performed using molecular tagging velocimetry (MTV). 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 ±0.5km/s were measured.

Review of Fluorescence-Based Velocimetry Techniques to Study High-Speed Compressible Flows

“…10. Figure 11 shows measurements along profiles spaced 0.57, 1.97, and 2.97 cm downstream of the nozzle exit of the arc jet, denoted by horizontal bars.…”

“…The measurements, detailed in Ref. 10, were intended to provide an improved understanding of the operation of that arcjet's flowfield characteristics. In the measurements, the spectral position of the laser was scanned over a small wavelength range about the excitation spectrum of the relatively well-isolated Q 11 (13) transition of NO.…”

Quantitative Spectral Radiance Measurements in the HYMETS Arc Jet

“…Such sharp discontinuities were observed in this facility using NO PLIF, which is an imaging technique with sub-microsecond time resolution. 2 The NO PLIF showed unsteady motion of the bow shock wave. The current measurements are time-averaged for a minimum of 3 msec and up to 30 seconds.…”

“…Nitric oxide (NO) planar laser-induced fluorescence (PLIF) has recently been used in the HYMETS arcjet to measure axial and radial velocities as well as to visualize the flow. 2 Several nonintrusive measurement techniques have been applied by others to arcjet flows. Diode laser absorption has been demonstrated for making simultaneous velocity and temperature measurements of an argon arcjet plume.…”

Hypersonic Boundary Layer Measurements with Variable Blowing Rates Using Molecular Tagging Velocimetry

“…5 was subtracted in quadrature as described in Ref. 17. Thus, the U' values indicated are a measure of the fluctuations in the flow.…”