MEASUREMENT AND ANALYSIS OF NITRIC-OXIDE RADIATION IN AN ARCJET FLOW

Radiation from the nitric oxide (NO) band systems emitted by the flow in the test section of a 20-MW arcjet wind tunnel was measured and compared with the computed values for the purpose of testing the validity of an existing thermochemical model. The settling chamber pressure and enthalpy were 2.4 atm and 28 +/- 10 MJ/kg, respectively. The measurements were made using photographic films in the wavelength region from 225 to 305 nm. Of the four band systems of NO (beta, gamma, delta, and epsilon), vibrational transitions were observed from only the upper v' = 0 levels. Excitation temperatures were deduced by comparing the experimental spectrum with those calculated using the nonequilibrium radiation code NEQAIR. The rotational, vibrational, and electronic excitation temperatures deduced from the data were T(r) = 560 +/- 50 K, T(v) less-than-or-equal-to 950 +/- 50 K, and T(ex) = 11,500 +/- 520 K, respectively. A multitemperature nonequilibrium nozzle flow code NOZNT was used to calculate the nozzle flow. The calculated temperatures were T(r) = 560 K, T(v) = 950 K, and electron thermal temperature T(e) = 6100 K, respectively at 30 MJ/kg. The presented results show that by using the centerline enthalpy value deduced from heat transfer measurement and the NOZNT code, one can predict the freestream conditions in an arcjet wind-tunnel flow fairly well.