DSMC Simulation of a Radiating Hypersonic Flow

This research continues development of radiative results with the direct simulation Monte Carlo (DSMC) method for an 11-species air hypersonic flow. A 10.28 km/s, 0.2 Torr hypersonic shock tube experiment in rarefied air is simulated using the Computation of Hypersonic Ionizing Particles in Shocks (CHIPS) DSMC code and CHIPS results are post processed by the NEQAIR line-by-line radiative solver to produce emission spectra. The chosen scenario reproduces the conditions of recent NASA Electric Arc Shock Tube (EAST) experiments which are used as benchmarks for the simulated emission spectra. Several improvements to the CHIPS code were completed to advance the comparison with radiative experiments. An updated 11-species air chemical reaction rate set was developed and analyzed to ensure compatibility with the chemical reaction models. In addition, species specific electronic collision numbers were found to be necessary for the electronic excitation model used in CHIPS. The CHIPS/NEQAIR interconnect was also updated to calculate radiative quantities directly from excited state populations. This required development of an ungrouping method which utilizes a polynomial least squares curve fit to ungroup a set of states using the local slope in a Boltzmann plot. With these improvements, reasonable agreement was observed between simulations and experimentally measured spectra in the VUV, UV/Vis, Vis/NIR, and IR spectral ranges and several areas of improvement were identified. The results of this hypersonic scenario represent the nominal simulation of a future sensitivity analysis of CHIPS input parameters.