Temperature and Density Measurements in Free Jets and Shock Waves

Abstract

The fluorescence stimulated by a 17.5‐kV electron beam probe was used to obtain measurements of rotational temperature and gas density in supersonic nitrogen jets expanding from room temperature. The parameter P₀d (where P₀ is the stagnation pressure in Torricelli and d is the orifice exit diameter in millimeters) was varied from 15 to 480 Torr‐mm. Density measurements were made using an interference filter‐photomultiplier combination. The experimental density data follow the axial isentropic density distribution in regions of rotational nonequilibrium. Rotational temperature measurements were obtained from rotational spectra of the 0–0 band of the N₂⁺ first negative system. The experimentally determined rotational temperatures, which initially follow the axial isentropic temperature distribution in a free jet, depart from the isentropic curve at low temperatures and freeze at a constant value, indicating a substantial degree of nonequilibrium in the expansion. A shock holder was inserted in the jet and a number of shock waves in the range M = 4 to M = 15 were investigated. Rotational spectra indicate a large departure from a Boltzmann distribution in the rotational levels in the center of a shock front. An apparent non‐Boltzmann rotational distribution in the jet expansion was also observed.