CFD Predictions of High Enthalpy Shocks in Nitrogen

Computational fluid dynamics simulations are performed to complement the understanding of shocked gas dynamics from the experiments conducted in Electric Arc Shock Tube facility at NASA Ames Research Center. This analysis focuses on pure nitrogen, where the EAST data is available for shock speeds ranging from 6-11 km/s. An innovative approach is used to compute the shock tube flow evolution in a time-accurate manner where the governing equations are solved in a moving-frame of reference using active shock-tracking. The numerically simulated shock front attains a near-constant speed soon after it is fully formed (i.e., after ten tube-diameters of shock travel) beyond which the post-shock gas properties change relatively slowly. The post-shock gas dynamics are dominated by dissociation at lower speeds, whereas higher shock speeds show increasing degrees of ionization up to 10-15 cm behind the shock. Post-shock electron number densities have been previously reported and show above equilibrium values for shock speeds less than 10 km/s. While there are differences between the two due to the modeling assumptions and the simplifications of the experimental facility made in the numerical modeling, the CFD predicted gas behavior shows a good qualitative match with EAST electron number density data. The analyses provide deeper insight into the shocked gas behavior for a range of test conditions.