Measurement of Velocity and Pressure of Gases in Rocket Flames by Spectroscopic Methods

Abstract

A method for measuring the gas flow velocity in hot high velocity exhaust flames is described. This method is based on the doppler shift of wavelength of the sodium or lithium spectral radiation from the flame when viewed at different angles relative to the flame axis. The same apparatus may be used to measure the gas pressure from the pressure shift of wavelength of the sodium radiation. A Fabry-Perot interferometer and camera assembly was used to determine the small shift in wavelengths. It was concluded that the absolute accuracy of any one velocity measurement by this method is about ±1.5×104 cm/sec, while that of any one pressure measurement is about ±0.3 atmosphere. The method is therefore applicable to flames of very high velocity and to pressures of at least a few atmospheres.