Nonequilibrium Air Radiation Research Articles

Measurement of Radiative Nonequilibrium for Air Shocks Between 7 and

This paper describes a characterization of thermochemical nonequilibrium radiance for shock speeds between 7 and in the NASA Ames Electric Arc Shock Tube. Data are spectrally resolved from 190 to 1450 nm and spatially resolved behind the shock front on the order of 10 cm. The data are analyzed in terms of a spectral nonequilibrium metric, defined as the average radiance within of the peak radiance and presented in a format that may be used to test predictive nonequilibrium radiation tools. The data collected in two shock tubes of differing diameter (10 and 60 cm) at the same nominal shock condition agree within 30%. The spectra are compared with simulations using the DPLR/NEQAIR software tools using a combination of different modeling options (reaction rates, energy mode accounting, and electron impact excitation rates). The results show mixed agreement, with no one modeling option being a clear preference. This suggests that the data may be used to help to identify improvements to methodologies for modeling nonequilibrium air radiation.

Emission spectroscopy of nitric oxide in laser-induced plasma

In this paper, we investigate the laser-induced breakdown spectra of nitric oxide. Nitric oxide spectra are studied from laser-induced plasma emissions from plasma initiated both in laboratory air. Temperatures are inferred from the spectroscopic emissions using two methods. Spectra are fit to theoretical calculations of the diatomic spectra using the method of diatomic line strengths. For a time delay of 25 μs the temperature is found to be 6800 Kelvin. Comparisons are also provided to previously determined temperatures using a non-equilibrium air radiation fitting (NEQAIR) program.

Simulation of Radiative Transfer in Nonequilibrium Plasmas Containing N and O Species Based on the Approximate Collision-Radiative Method

An approximate collision-radiative method is developed to calculate energy level populations of atoms and applied to simulate radiative transfer in a shock layer. Considering nonequilibrium plasmas with the electronic temperature below 20000 K, we introduce correction factors to the Saha—Boltzmann equation and simplify the master equation of the full collision-radiative model. Based on the method, the error of heat flux is smaller than 5% in a two-cell problem and smaller than 7% in the Stardust re-entry flow field compared with the correlated-k method. Furthermore, almost a factor of 2 is obtained in the improvement of computational efficiency compared with the nonequilibrium air radiation (NEQAIR) code. The results show that the present method is reliable and efficient.

Development of Coupled Particle Hypersonic Flowfield- Photon Monte Carlo Radiation Methods

DOI: 10.2514/1.44645 With its fast reentry speed, the Stardust vehicle generated a strong shock region ahead of its blunt body with a translational temperature in excess of 60,000 K. Such an extreme Mach number flow is sufficiently energetic to initiate gas ionization processes and thermal and chemical ablation processes. The generated charged species affect nonequilibrium atomic and molecular energy distributions and shock layer radiation. In this work, we present the first loosely coupled direct simulation Monte Carlosimulations with the particle-based photon Monte Carlo method to simulate high-Mach-number reentry flows in the near-continuum to transitional flow regimes. Eleven species including five ionization processes were modeled in direct simulation Monte Carlo, and the average ion velocity model was used to simulate the electron motion. The degree of ionization is predicted to be between 3–7% along the stagnation line for altitudes of 68.9 and 81 km, and the maximum translational and electron temperatures are approximately 60,000 and 20,000 K, respectively. To efficiently capture the nonequilibrium radiation generated by this flow, emission and absorption coefficient databases using the Nonequilibrium Air Radiation computational tool were generated. However, in contrast to the Nonequilibrium Air Radiation computational tool, radiative transport was modeled by the particle-based photon Monte Carlo method instead of the simplified one-dimensional tangentslab approximation. It was found that the atomic nitrogen emission is approximately 1 order of magnitude higher than the atomic oxygen emission along the stagnation line due to the higher concentration of atomic nitrogen at this altitude.Theradiationenergychangecalculatedbytheparticle-basedphotonMonteCarlomethodwascoupledwith the direct simulation Monte Carlo calculations, and it was found that although the atomic nitrogen and atomic oxygenatomicradiationdoesnothaveanimportantimpactonthe flowfieldat81km,thestrongerradiationmodified the flowfield and heat flux at the wall at an altitude close to peak heating.

超軌道速度再突入物体前面における対流・ふく射熱伝達の推算

The convective and radiative heat transfer rates are calculated over the super-orbital reentering body surface like the MUSES-C capsule. Thermally and chemically nonequilibrium 11-species (O2, N2, O, N, NO, O+2, N+2, O+, N+, NO+ and e-) air is considered using Park's two temperature model. Chemical species number densities and temperature distributions are obtained by solving the Navier-Stokes equations and the vibrational-electronic energy conservation equation, using a Harten-Yee-type upwind TVD scheme. For the isothermal wall condition the minimum grid interval is set to 1μm in order to maintain the cell Reynolds number of O(1). The radiative heat transfer rate is calculated by integrating the radiative heat transfer equation using emission and absorption coefficients that are determined by NEQAIR (Nonequilibrium Air Radiation) and SPRADIAN (Structured Package for Radiation Analysis). Those results are compared with convective heat transfer rate.

Assessment of a two-temperature kinetic model for dissociating and weakly ionizing nitrogen

The validity of the author's two-temperature, chemical/kinetic model which the author has recently improved is assessed by comparing the calculated results with the existing experimental data for nitrogen in the dissociating and weakly ionizing regime produced behind a normal shock wave. The computer program Shock Tube Radiation Program (STRAP) based on the two-temperature model is used in calculating the flow properties behind the shock wave and the Nonequilibrium Air Radiation (NEQAIR) program, in determining the radiative characteristics of the flow. Both programs were developed earlier. Comparison is made between the calculated and the existing shock tube data on (1) spectra in the equilibrium region, (2) rotational temperature of the N2(+) B state, (3) vibrational temperature of the N2(+) B state, (4) electronic excitation temperature of the N2 B state, (5) the shape of time-variation of radiation intensities, (6) the times to reach the peak in radiation intensity and equilibrium, and (7) the ratio of nonequilibrium to equilibrium radiative heat fluxes. Good agreement is seen between the experimental data and the present calculation except for the vibrational temperature. A possible reason for the discrepancy is given.