Chul Park

Review of Chemical-Kinetic Problems of Future NASA Missions, II: Mars Entries

A number of chemical-kinetic problems related to phenomena occurring behind a shock wave surrounding an object flying in the earth atmosphere are discussed, including the nonequilibrium thermochemical relaxation phenomena occurring behind a shock wave surrounding the flying object, problems related to aerobraking maneuver, the radiation phenomena for shock velocities of up to 12 km/sec, and the determination of rate coefficients for ionization reactions and associated electron-impact ionization reactions. Results of experiments are presented in form of graphs and tables, giving data on the reaction rate coefficients for air, the ionization distances, thermodynamic properties behind a shock wave, radiative heat flux calculations, Damkoehler numbers for the ablation-product layer, together with conclusions.

Calculation of real-gas effects on blunt-body trim angles

The effect of vibrational excitation and dissociation at high temperatures on the trim angle of attack of a blunt lifting body is calculated for a nonequilibrium flow regime in air using a CFD technique. The vibrational-electronic temperature and the species densities are calculated assuming the flow to be in a nonequilibrium state. The forebody flow of a two-dimensional blunt body of the shape of the Apollo Command Module at a finite angle of attack is calculated. The results show that the pitching moment around a reference point is larger and the trim angle of attack is smaller for a reacting gas than for a perfect gas. The calculated shift in the trim angle due to the real-gas effect is of the same order as that seen during the Apollo flights.

Comparison of electron and electronic temperatures in recombining nozzle flow of ionized nitrogen--hydrogen mixture. Part 1. Theory

Relaxation of the population distribution of electronic states is studied theoretically for a highly ionized nitrogen-hydrogen mixture expanding through a nozzle wherein the hydrogen content is less than 0.1%. The analysis incorporates quantum-mechanical rate coefficients, and considers the effects of wall cooling and absorption of radiation. Calculations are carried out for a condition produced experimentally. Visible and infrared line radiations from nitrogen and hydrogen were measured with a spectrograph. The geometry and stagnation conditions were those calculated theoretically. The experiment confirms quantitatively the predictions that the electronic excitation temperatures of hydrogen and (3P) core states of nitrogen are higher than the electron temperature, and that (3P) excitation temperatures exhibit maxima within the nozzle.

Computation of nonequilibrium, supersonic three-dimensional inviscidflow over blunt-nosed bodies

Subscripts B A computer code based on the method of characteristics is applied to the study of twoand three-dimensional chemical nonequilibrium flow over sharpand blunt-nosed bodies. Nonequilibrium flow over a wedge is used to show the approach to equilibrium flow and to demonstrate the nature of the reaction zone behind the bow shock wave. The structure and development of a blunt-body entropy layer in nonequilibrium flow is examined for a blunt cone at zero incidence. Three dimensional computations for the Space Shuttle body at 30 deg angle of attack are presented. A nondimensional scaling parameter, the Damkohler number (the ratio of flow time to chemical reaction time) is calculated and its significance discussed. .

Shock tube study of ionization rates of NaCl-contaminated argon

Electron density, electron temperature, and concentration of excited sodium atoms are measured in the weakly ionized regime behind a shock wave in impure argon in a shock tube using microwave techniques and spectrally resolved radiometry. Evidence is presented to show that an apparent increase in the rate of ionization is due to electron detachment of negative chlorine ions produced from sodium chloride vapor contained as an impurity. To be consistent with this chemical model, rate coefficients are found for 5500<T<8600u2009°K to be as follows: for NaCl+Ar+5.8 eV→Na++Cl−+Ar, k4=0.082exp(−67 315/T)/T2 cm3 sec−1; for Cl−+Ar+3.61 eV→Cl+e+Ar, k5=6×10−12exp(−41 900/T) cm3 sec−1; and for the branching ratio between the reaction NaCl+Ar+5.8 eV→Na++Cl−+Ar(k4) and reaction NaCl+Ar+4.27 eV→Na+Cl+Ar(k3), k4/k3=1.6×104exp(−17 760/T). Electron temperature is lower than heavy particle temperature by roughly 1000u2009°K. The electron‐argon impact ionization rate coefficient is a weak function of electron temperature in contradi...

Calculation of radiation from argon shock layers

Abstract The accuracy of calculations of the radiation emissions from argon plasmas produced by the shock layers over blunt bodies is assessed. The existing theoretical and experimental spectroscopic data on argon are collated. A set of such data is selected for use in the radiative transfer calculations. Calculations are performed for the stagnation regions of the shock layers over laboratory-sized models using these data, and the results are compared with the existing experimental results obtained in a shock-tube. Through this comparison and a parametric study it is shown that radiative heat fluxes at the stagnation point in an argon environment can be calculated within an uncertainty of about 15%. It is shown also that radiative heat fluxes of the order of 100 kW/cm2 can be produced in the existing laboratory facilities.

Nitric oxide production by Tunguska meteor

Abstract The nonequilibrium chemical processes of nitric oxide formation are computed for the wake of the Tunguska meteor of 1908. The wake characteristics are derived by carrying out an optically-thick radiation field analysis for ablation of the meteoroid. The wake flow field is approximated by a one-dimensional, well-stirred reactor model. Known characteristics of the Tunguska event are imposed as constraints, and three controlling parameters—chemical composition, density, and velocity—are varied over a range around the values derived by Korobeinikov et al. (1976) and Petrov and Stulov (1975). The calculation shows that at least 19 million tons of nitric oxide is produced between the altitudes of 10 and 50 km. The anomalous atmospheric phenomena following the event are attributed to the reactions involving nitric oxide thus produced and atmospheric oxone. It is speculated that the nitric oxide produced by the event fertilized the area near the fall, causing the observed rapid plant growth.

Electron impact excitation rate coefficients for hydrogen, helium and alkali atoms

Abstract The rates of electron impact excitation of bound electronic states are calculated by interpolating the existing quantum-mechanical theories and applying an empirical correction. The calculation is done for hydrogen, helium, lithium, sodium, potassium, rubidium and cesium. The resulting rate coefficients are expressed by two parameters, the values of which are presented in tables. The error of the present calculation is estimated by comparing with available experimental data to be within a factor of approximately 2.

Ablation of Carbonaceous Materials in a Hydrogen-Helium Arcjet Flow

The stagnation-point ablation rates of a graphite, a carbon-carbon composite, and four carbon-phenolic materials are measured in an arc-jet wind tunnel with a 50 percent hydrogen-50 percent helium mixture as the test gas. Flow environments are determined through measurements of static and impact pressures, heat-transfer rates to a calorimeter, and radiation spectra, and through numerical calculation of the flow through the wind tunnel, spectra, and heat-transfer rates. The environments so determined are: impact pressure approximately equal to 3 atm, Mach number approximately equal to 2.1, convective heat-transfer rate approximately equal to 14 kW/sq cm, and radiative heat-transfer rate approximately equal to 7 kW/sq cm in the absence of ablation. Ablation rates are determined from the measured rates of mass loss and recession of the ablation specimens. Compared with the predicted ablation rates obtained by running RASLE and CMA codes, the measured rates are higher by about 15 percent for all tested materials.

Spectral line intensities in a nonequilibrium nitrogen plasma

Abstract For given ratios of nonequilibrium ground state number density to equilibrium ground state number density, and given electron temperatures, the relative populations of excited states of atomic nitrogen in a collision-dominated nonequilibrium plasma, consisting of atoms, singly charged ions, and electrons, are calculated by the method of Bates, Kingston, and McWhirter. This method uses Gryzinskis semiclassical cross sections for the collisional excitation of electronic states of an atom. From the resulting populations, the spectral intensities of two prominant visible lines are calculated assuming the plasma to be optically thin for these lines. It is shown that, with the exception of a decaying plasma at temperatures greater than 8000°K, the calculated nonequilibrium intensities disagree with the equilibrium spectral line intensities that would be conventionally employed to determine the temperature of a plasma in equilibrium.