Multiband Radiation Model for Simulation of Galileo Probe Entry Flowfield

Abstract

Received 4 March 2005; revision received 1 October 2005; accepted for publication 3 October 2005. Copyright c © 2006 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. Copies of this paper may be made for personal or internal use, on condition that the copier pay the $10.00 per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923; include the code 0887-8722/06 $10.00 in correspondence with the CCC. ∗Researcher, Computational Science Research Group, Institute of Aerospace Technology; smatsu@chofu.jaxa.jp. Member AIAA. †Graduate Student, Department of Aerospace Engineering. ‡Research Associate, Department of Aerospace Engineering. Member AIAA. §Professor, Institute of Fluid Science, Sendai 980-8577. Associate Fellow AIAA. ¶Professor, Department of Aerospace Engineering. Associate Fellow AIAA. revealed that there was a significant discrepancy of the final recession profile from that given by the preflight prediction. Indeed, the amount of recession occurred at the stagnation region deduced from the flight data was almost three-fourths and that at the frustum region was almost double when compared with those given by the preflight prediction.2 This discrepancy has yet to be explained. Recently, in our previous study,3 we succeeded in reproducing the large recession occurring at the frustum region and gave one consistent explanation for why the radiative heat flux along the frustum region of the Galileo probe was larger than the preflight predictions. It was found that the number densities of radiation-absorbing carbonaceous species in the ablation layer were substantially decreased by excessive diffusion and dissociation reactions caused by the enhanced turbulence effects. To obtain this result, an accurate calculation of a strongly radiating flowfield over the Galileo probe that accounted for detailed spectral radiative properties was used. The line-by-line method4 is known to yield the most accurate spectral radiative properties of high-temperature gases. However, it is not suitable for coupling with a flowfield calculation because of its enormous computational load. The modern multiband radiation models can reduce the computing time of the line-by-line calculation at least by a factor of 100 and reproduce the line-by-line result within a small error.5,6 In these models, it is customary to assume that the absorption coefficients depend only on temperature, assuming in advance typical electron number densities within the shock layer. This treatment, however, is not suitable for the Galileo probe entry case because the line shape of atomic hydrogen has significant dependence on electron number density. In this study, therefore, we give a new implementation of the radiation multiband model that depends on both the local temperature and electron number density.