Ilyoup Sohn

Advanced Radiation Calculations of Hypersonic Reentry Flows Using Efficient Databasing Schemes

Efficient schemes for databasing emission and absorption coefficients are developed to model radiation from hypersonic nonequilibrium flows. For bound-bound transitions, spectral information including the line-center wavelength and emission and absorption coefficients is stored for typical air plasma species. Since the flow is nonequilibrium, a rate equation approach including both collisional and radiatively induced transitions is used to calculate the electronic state populations, assuming quasi steady state. The general Voigt line-shape function is assumed for modeling the line-broadening. The accuracy and efficiency of the databasing scheme was examined by comparing results of the databasing scheme with those of NEQAIR for the Stardust flowfield. An accuracy of approximately 1 % was achieved with an efficiency about three times faster than the NEQAIR code.

Modeling of Electronic Excitation and Radiation for Hypersonic Reentry Flows in DSMC

The current work implemented excited levels of atomic N and corresponding electron impact excitation/de-excitation and ionization processes in DSMC. Results show that when excitation models are included, the Starduct 68.9 km re-entry flow has an observable change in the ion number densities and electron temperature. Adding in the excited levels of atoms improves the degree of ionization by providing additional intermediate steps to ionization. The extra ionization reactions consume the electron energy and reduce the electron temperature. The DSMC results of number densities of excited levels are lower than the prediction of quasi steady state calculation.

Effect of Nonlocal Vacuum Ultraviolet Radiation on Hypersonic Nonequilibrium Flow

during the excitation process of the same radiating gas species. This interaction affects the distribution of electronic state populations and, in turn, the radiative transport. The radiative transition rate in the excitation/deexcitation processes and the radiative transport equation must be coupled to account for nonlocal effects. A quasi-steady-state model is presented to predict the electronic state populations of radiating gas species taking into account nonlocal radiation. The definition of the escape factor that is dependent on the incoming radiative intensity from over all directions is presented. To perform accurate and efficient analyses of radiation from a chemically reacting flowfield, thedirect simulation MonteCarloandthefully three-dimensional photonMonteCarloradiative transportmethods are used. The effect of the escape factor on the distribution of electronic state populations of the atomic N and O radiating species is examined in a highly nonequilibrium flow condition, and the corresponding change of the radiative heat flux due to the nonlocal radiation is also investigated. It is found that inclusion of the escape factor increasestheupperelectronicstatepopulationsbyaboutafactorof2withasimilarincreaseintheradiativeheat flux to the vehicle surface.

DSMC modeling of NO formation for simulation of radiation in hypersonic flows

The current work has implemented in DSMC discrete vibrational levels of N2 and the transitions between them as well as the dissociation of nitrogen molecules and formation of NO molecules. The vibration-translation transition models assessed include LarsonBorgnakke, Schwartz-Slawsky-Herzfeld (SSH), and Forced Harmonic Oscillator (FHO) models. Total Collision Energy (TCE) and QCT models for the NO formation reaction are considered. The effect of the models on the flowfield is explored and comparisons are made. Improved NO radiation modeling is proposed by employing quenching rates from most-recent experiments. Comparisons of electronic state populations and the corresponding radiative spectra among the neutral-impact excitation models are made. It is validated that vibrational band spectral structure of NO radiation is strongly influenced by vibrational temperature profiles along a line of sight.

Modeling of electronic excitation and radiation in non-continuum hypersonic reentry flows

The modeling of hypersonic radiation in non-equilibrium, non-continuum flows is considered in the framework of the direct simulation Monte Carlo (DSMC) approach. The study explores the influence of electronic states on the flow chemistry and degree of ionization as well as the assumption that the electronic states can be described by a steady state solution to a system of rate equations of excitation, de-excitation, and radiative transfer processes. The work implements selected excited levels of atomic nitrogen and oxygen and the corresponding electron impact excitation/de-excitation and ionization processes in DSMC. The simulations show that when excitation models are included, the degree of ionization in the Stardust transitional re-entry flow increases due to additional intermediate steps to ionization. The extra ionization reactions consume the electron energy to reduce the electron temperature. The DSMC predicted excited state level populations are lower than those predicted by a quasi steady state c...

Study of Emission Turbulence-Radiation Interaction in Hypersonic Boundary Layers

Direct numerical simulations are conducted to study the effects of emission turbulence-radiation interaction in hypersonic turbulent boundary layers, representative of the Orion Crew Exploration Vehicle at peak-heating condition during reentry. A nondimensional governing parameter to measure the significance of emission turbulence-radiation interaction is proposed, and the direct numerical simulation fields with and without emission coupling are used to assess emission turbulence-radiation interaction. Both the uncoupled and coupled results show that there is no sizable interaction between turbulence and emission at the hypersonic environment under investigation. An explanation of why the intensity of emission turbulence-radiation interaction in the hypersonic boundary layer is smaller than that in many combustion flows is provided.

Effects of non-maxwellian distributions on shock-layer radiation from hypersonic reentry flows

Nomenclature A = Einsteincoefficient for spontaneousemission,s−1 orcm s−1 f = electron velocity distribution function, s∕m h = Planck’s constant, 6.6262 × 10−34 Js i, j = electronic state K = rate coefficient for collisional transition, cm s−1 l = total number of electronic states n = number density, m−3 n0 = total atom-related species number density, m −3 Te = electron temperature, K Trot = rotational temperature, K Ttr = translational temperature, K Tvib = vibrational temperature, K t = time, s V = velocity, m∕s w = speed, m∕s X = horizontal coordinate of direct simulation Monte Carlo domain for the Stardust geometry, m Y = vertical coordinate of direct simulation Monte Carlo domain for the Stardust geometry, m ν = frequency, s ρ = escape factor σ = cross section, m

State specific vibrational relaxation and dissociation models for nitrogen in shock wave regions

This work studies the interaction of the DSMC vibrational relaxation models and dissociation of molecular nitrogen at moderate Mach numbers where such processes are important. The total collision energy (TCE) and QCT models for the N2 dissociation reaction were considered and the dissociation from different N2 vibrational excited states was included in the simulations. It was found that the use of the QCT rates compared to the usual, TCE model gave a substantially higher degree of dissociation and smaller shock width due to the non-equilibrium distribution in the vibrational states.

Development of magnetron sputtering simulator with GPU parallel computing

Sputtering devices are widely used in the semiconductor and display panel manufacturing process. Currently, a number of surface treatment applications using magnetron sputtering techniques are being used to improve the efficiency of the sputtering process, through the installation of magnets outside the vacuum chamber. Within the internal space of the low pressure chamber, plasma generated from the combination of a rarefied gas and an electric field is influenced interactively. Since the quality of the sputtering and deposition rate on the substrate is strongly dependent on the multi-physical phenomena of the plasma regime, numerical simulations using PIC-MCC (Particle In Cell, Monte Carlo Collision) should be employed to develop an efficient sputtering device. In this paper, the development of a magnetron sputtering simulator based on the PIC-MCC method and the associated numerical techniques are discussed. To solve the electric field equations in the 2-D Cartesian domain, a Poisson equation solver based...

Challenges of Modeling of Electronic State Specific Processes for Hypersonic Reentry Flows in DSMC

The modeling of hypersonic radiation in non-equilibrium, non-continuum flows is considered in the framework of the direct simulation Monte Carlo approach. The study explores the influence of electronic states on the flow chemistry and degree of ionization as well as the assumption that the electronic states can be described by a steady state solution to a system of rate equations of excitation, de-excitation and radiative transfer processes. The work implements selected excited levels of atomic nitrogen and oxygen and the corresponding electron impact excitation/de-excitation and ionization processes in DSMC. The simulations show that when excitation models are included, the degree of ionization in the Stardust transitional re-entry flow increases due to additional intermediate steps to ionization. The extra ionization reactions consume the electron energy to reduce the electron temperature. The DSMC predicted excited state level populations are lower than those prediction by a quasi steady state calculation, but, the differences can be understood in terms of the flow distribution functions.