Numerical and experimental studies of an arc-heated nonequilibrium nozzle flow

The arc-heated high-temperature gas is rotationally and vibrationally excited, and partially dissociated and ionized. When such gas flows inside a nozzle, energy transfers from rotational and vibrational energy modes to translational energy mode, and, in addition, recombination reactions occur. These processes are in thermal and chemical nonequilibrium. The present computations treat arc-heated nonequilibrium nozzle flows using a six temperature model (translational, rotational, N₂ vibrational, O ₂ vibrational, NO vibrational and electron temperatures), and nonequilibrium chemical reactions of air. From the calculated flow properties, emission spectra at the nozzle exit were re-constructed by using the code for computing spectra of high temperature air. On the other hand, measurements of N⁺₂(l-) emission spectra were conducted at the nozzle exit in the 20 kW arc-heated wind tunnel. Vibrational and rotational temperatures of N₂ were determined using a curve fitting method on N ⁺₂(1-) emission spectra, with the vibrational and rotational temperatures for N₂ and N⁺₂ being assumed equal. Comparison of the measured and computed results elucidated that the experimental temperatures were larger than the computed ones. At present, we are trying to reveal the main reason for the discrepancy between the computed and measured N₂ vibrational and rotational temperatures.