Potential of Glow-Discharge Flow Measurement in Hypersonic Low-Density Flows

Abstract

In this study, a simple model was developed to describe the mechanism behind a nonintrusive method that uses air glow discharge to simultaneously measure the gas density and temperature in low-density, short-duration hypersonic facilities. The developed model revealed that the emission intensity of the second positive band system of nitrogen molecules varies linearly with the gas density, which was firmly supported by spectroscopic observations characterizing the glow spectra. A laminar separated boundary layer was visually distinguishable via variations in the emission color reflected on a uniform positive column, along which traverse measurements were performed using miniature spectrometers. The experimental spectra agreed fairly well with synthetic ones calculated by substituting gas temperature distribution determined from computational fluid dynamics. In contrast, the temperature was not found to be a crucial factor determining the emission color distribution. The color was instead found to vary with the ratio of the emission intensity of the first positive band system to that of the second one. The principle of the variation in emission color implies that the mechanism explaining the variation will be more complex than what is assumed in existing models.