A shock tube study on nonequilibrium radiation of strong shock waves in low-density air

Nonequilibrium radiation behind strong shock waves in low-density air is studied in terms of a computer-aided, high-speed photography using a gated I. I. CCD camera system for shock waves generated by a free-piston, double-diaphragm shock tube. The range of shock velocity is from 9 km/s to 12 km/s at the initial pressure 13.3 Pa. Numerical simulation for radiation profiles is also performed using a three-temperature model. It is found from a two-dimensional, time-frozen photography for the total radiation profile that the shock velocity for the transition criteria from I-peak profile to 2-peaks profile is about 11 km/s, and that there are some discrepancies between observed and calculated profiles. Some remarkable phenomena are observed from the time-resolved spectroscopy: e.g., the longer radiation duration of the N-2(+)(1-)(1, 0) line and the temporal oscillations of the intensities of spectral lines of the N-2(+)(1-) band system. A comparison between observed and calculated streak images of the time-resolved spectroscopy is also presented.