Enthalpy Distributions of Arc Jet Flow Based on Measured Laser Induced Fluorescence, and Heat Flux and Stagnation Pressure Distributions

Abstract

The centerline total enthalpy of arc jet flow is determined using laser induced fluorescence of oxygen and nitrogen atoms. Each component of the energy, kinetic, thermal, and chemical can be determined from LIF measurements. Additionally, enthalpy distributions are inferred from heat flux and pressure probe distribution measurements using an engineering formula. Average enthalpies are determined by integration over the radius of the jet flow, assuming constant mass flux and a mass flux distribution estimated from computational fluid dynamics calculations at similar arc jet conditions. The trends show favorable agreement, but there is an uncertainty that relates to the multiple individual measurements and assumptions inherent in LIF measurements.

Consolidated Laser-Induced Fluorescence Diagnostic Systems for the NASA Ames Arc Jet Facilities

“…LIF techniques have been applied for chemistry studies in various arc jet environments, including H 2 , 4 H 2 -CH 4 , 5 H 2 -Ar-CH 4 , 6 N 2 -CH 4 , 7 N 2 -CO 2 , 8 and air. [9][10][11][12][13][14][15][16][17][18][19][20] In a LIF measurement of a flowing gas, a laser pulse from a wavelength-tunable laser source excites a specific transition from the ground electronic state in the target atom or molecule; within a few tens of nanoseconds, the excited state relaxes to an intermediate electronic state by emitting a photon. Spectroscopic analysis of the absorbed laser radiation and emitted fluorescence yields quantitative information about the probed species, including initial (or ground) state populations and temperature.…”

“…Two additional systems were developed and used at NASA in the late 2000s -one for the 60 MW Interaction Heating Facility (IHF) at NASA Ames, 16 and another for the 10 MW Test Position 2 (TP-2) facility at NASA Johnson Space Center. 18 Both of these later implementations built upon previous experience from the Ames AHF LIF system. The new systems further expanded performance and efficiency by introducing a calibration source engineered for use in the arc jet facilities, advanced data acquisition instrumentation, and custom data acquisition and instrument control software.…”