Shock Layer Radiation Analysis using a Hypervelocity Shock Tube (HVST)

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Spectroscopic measurement is conducted using a free-piston double-diaphragm shock tube to investigate the nonequilibrium phenomena in the shock layer. The shock velocity and spectrum position correlated to the shock front are determined using a double-laser schlieren measurement system for precise localization. Emission spectra of N2(1+), N2(2+) and N2+(1−) band systems are obtained by means of time-frozen imaging spectroscopy. A spectrum fitting method is used to determine the rotational and vibrational temperatures from the measured spectra, and temperature distribution correlated to the shock front is finally obtained. The measured rotational temperatures are in high nonequilibrium with the translational temperature expected from the numerical prediction of the two-temperature model. The measured rotational temperature for N2(2+) is lower than those for N2(1+) and N2+(1−) immediately behind a shock wave. Hence, rotational relaxation for the N2C state looks slower than those for the N2B and N2+ B states. On the contrary, the measured vibrational temperatures for N2(1+), N2(2+) and N2+(1−) are close to each other, and agree well with the numerical prediction of the two-temperature model. The experiment and numerical analysis suggest that the electronic excitation temperature is in nonequilibrium with the vibrational temperature.

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