Spectroscopic study of arc-heated nonequilibrium nitrogen flow before a blunt body

Abstract

An arc-heated wind tunnel is being used to produce nitrogen gas flow with high enthalpy at a Mach number of 5.0 to investigate complicated nonequilibrium phenomena around a blunt body flying at high speed. The flow field with and without an axisymmetric blunt body in the test section is studied by spectroscopic measurements. Specifically, the vibrational and rotational temperature distributions of nitrogen molecule are measured along the stagnation streamline of the body. It is found that the vibrational temperature begins to increase from 6mm upstream of the stagnation point, which corresponds to about 4.5mm before a shock wave produced by the body, and that it takes a maximum value between 3800 and 4500K at a location of 2mm upstream from the stagnation point. On the other hand, the rotational temperature also increases up to 2500 ~ 3500K at a location of 1mm. The vibrational and rotational temperature distributions for the case with no body are also measured for comparison. While the vibrational temperature shows a slightly decrease toward the downstream, the rotational temperature keeps a nearly constant value, which is lower than that of the vibrational temperature.