Simulation of flows in shock-tube facilities by means of a detailed chemical mechanism for nitrogen excitation and dissociation
A database was recently developed at NASA Ames Research Center for the dissociation and excitation rates of the rovibrational energy levels of nitrogen. This work is a first step toward the development of a simplified mechanism for 3-D simulations of atmospheric entry flows. First, we have derived a Boltzmann average dissociation rate based on rotational and vibrational temperatures. At thermal equilibrium, a very good agreement is obtained with the rate proposed by Park (1990). Significant discrepancies are observed in thermal non-equilibrium conditions. Then, we have developed a 0-D vibrational state-to-state collisional model to simulate a typical shock in a nitrogen flow based on vibrational-specific excitation and dissociation reaction rates derived by assuming a Boltzmann distribution of the rotational energy levels at the translational temperature. We have shown that the vibrational energy relaxation for the monoquantum excitation processes deviates significantly from the conventional Landau-Teller law. The dissociation process, coupled with the energy level relaxation dynamics, strongly depends on multi-quantum jump processes. Finally, we have implemented the multi-temperature dissociation rate in a 1-D code for shock-tube flows and have compared our results with experimental results.
excitation and dissociation of molecular nitrogen 447 and for excitation between all states
A rovibrational collisional model is developed to study the internal energy excitation and dissociation processes behind a strong shockwave in a nitrogen flow. The reaction rate coefficients are obtained from the ab initio database of NASA Ames Research Center. The master equation is coupled with a one-dimensional flow solver. The system of equations is solved for conditions expected for reentry into Earth’s atmosphere at 10 km/s. In addition, a coarse graining model is proposed by lumping the rovibrational energy levels into a smaller number of bins. The results obtained by means of the full rovibrational collisional model are compared to those obtained by means of a vibrational collisional model. Thermalization and dissociation occurs after a larger distance for the rovibrational collisional model compared to the distance predicted by means of the vibrational collisional model. This is expected to be the consequence of the assumption of equilibrium between the rotational energy and the translational energy, used for the vibrational collisional model, as opposed to the rovibrational collisional model. Finally, the coarse graining model allows an accurate description of the internal energy relaxation and dissociation processes based on a reduced number of equations.
Pioneer 10 Observations of the Ultraviolet Glow in the Vicinity of Jupiter
A two-channel ultraviolet photometer aboard Pioneer 10 has made several observations of the ultraviolet glow in the wavelength range from 170 to 1400 angstroms in the vicinity of Jupiter. Preliminary results indicate a Jovian hydrogen (1216 angstrom) glow with a brightness of about 1000 rayleighs and a helium (584 angstrom) glow with a brightness of about 10 to 20 rayleighs. In addition, Jupiter appears to have an extensive hydrogen torus surrounding it in the orbital plane of Io. The mean diameter of the torus is about equal to the diameter of the orbit of Io. Several observations of the Galilean satellites have also occurred but only a rather striking Io observation has been analyzed to date. If the observed Io glow is predominantly that of Lyman-α, the surface brightness is about 10,000 rayleighs.