Spectroscopic Measurements of Shock-Layer Flows in an Arcjet Facility

Abstract

Under two different test conditions, radiation emanating from the freestream and shock-layer flow over a 15.24-cm-diam blunt-body test article as measured in NASA Ames Research Center's 20 MW Aerodynamic Heating Facility Arcjet. The test gas was a mixture of air and argon. Spatially resolved emission spectra were obtained over a 2000-8900 A wavelength range using a charge-coupled device camera (1024 × 256 array) attached to a spectrograph. The optical system was calibrated using tungsten and deuterium radiation sources. Previously developed analytical tools were used to determine the following line-of-sight-averaged thermodynamic properties from the calibrated spectra: 1) rotational temperature of the freestream and 2) rotational and vibrational temperatures within the shock layer. Based on the variation in intensity of emission spectra along the stagnation streamline, shock standoff distance was determined. Two sets of data for each test condition were compared to evaluate the repeatability of measurements. Considering likely sources of errors, an uncertainty analysis was performed to estimate the error bounds of the determined properties