Modeling of Ultraviolet Radiation in Steady and Transient High-Altitude Plume Flows

Abstract

Ultraviolet radiation from hydrazine spacecraft thruster plumes interacting with ambient atomic oxygen is modeled for low-Earth-orbit conditions. Two numerical techniques that employ the direct simulation Monte Carlo method are applied for the rst time to the modeling of space plume radiation transient and three-dimensional ows. These ef cient procedures allow one to analyze the effect of atomic oxygen penetration of the thruster plume, which is a key factor in modeling rare ed space plume radiation. The overlay technique is used to model the transient ow evolution during the rst several seconds after motor ignition. Good agreement between modeling and experiment are obtained before 1-s motor burn time. The sensitivity of the plume radiation to the molecular total collision model is analyzed using the overlay technique, and the radiation spatial distribution was found to be strongly dependent on the temperature exponent of the coef cient of viscosity. Three-dimensional computations are conducted for different angles between the plume axis and the freestream directions, and the radiation maps for OH(A) and NH(A) are presented. Signi cant difference between OH(A) and NH(A) radiation elds as a function of the angle of attack is shown.

Studying of Atomic and Molecular Interaction Processes in Rarified Hypervelocity Expanding Flows by Methods of Emissive Spectroscopy

“…It should be noted, however, that NH(A→X) radiation intensity distribution may differ from the OH(A→X) one. This was indirectly proved above in Section 2.6.3 and supported by numerical modeling 20,21,22 . Nevertheless, coincidence of the radiation profiles in Figure 33 is not surprising, given substantially different response of the imager to the NH(A→X) and OH(A→X) UV radiation.…”

“…General problem inherent to all these efforts was uncertainty of the elastic cross-sections for collisions between atomic oxygen and plume molecules and complete absence of the cross-section energy dependence data for reaction (8.1). Spatial distribution of the glow radiation was found to be very sensitive to the choice of the elastic scattering model 21,23 , whereas absolute radiation intensity must have direct relation to the reaction (8.1) cross-section 4,21 . In this regard, proposed was to use the experimental data obtained on "Mir" space station for verification of the elastic collision models and derivation of the reaction (8.1) cross-section.…”

“…Modeling of the intensity spatial distribution showed its high sensitivity to the choice of elastic collision cross-sections 20,21,23 . So, comparison between measured and modeled intensity profiles may be effectively used for the elastic collision model verification at the collision energies of several eV.…”

“…The glow signal induction and decay time histories may be measured in different parts of the glow, providing a mean for verification of the models for non-stationary rarified expanding flows 21 . The glow intensity time histories measured at the initial stage along different lines of sight in the April 26, 2000 experiment are presented in Figure 35.…”

“…Task_C activity was particularly addressed to testing of commonly used collisional models at abovementioned energies of colliding partners. These tests seem to be well-timed, because all earlier simulations of the plume glow had one or another cross-section model involved 1,4,20,21,22,23 . Spatial distribution of the glow radiation was demonstrated to be sensitive to elastic collision cross-section choice.…”