Modeling of Stardust Entry at High Altitude, Part 1: Flowfield Analysis

摘要

The Stardust sample return capsule entered the Earth's atmosphere at a very energetic velocity of 12.6 km/s. In the present study, both continuum (computational fluid dynamics) and particle (direct simulation Monte Carlo) methods are used to analyze the forebody flow of the Stardust sample return capsule at altitudes of 81 and 71 km, where the flow is in the near-continuum regime. At the higher altitude, direct comparisons between baseline computational fluid dynamics and direct simulation Monte Carlo models give enormous differences in basic flowfield properties. To study the discrepancy between the solutions, a modified approach for determining the temperature used by computational fluid dynamics to control the dissociation and ionization reactions is investigated. The modified computational fluid dynamics and direct simulation Monte Carlo results are in significantly better agreement with each other, illustrating the strong sensitivity to chemistry modeling under these highly energetic conditions. Significant differences persist in temperatures near the capsule surface and in surface heat flux. Evaluation of local Knudsen numbers indicates that the flow experiences noncontinuum behavior in the shock front and at the capsule surface that explains the smaller heat flux predicted by direct simulation Monte Carlo. At the lower altitude, the flowfield results become less sensitive to details of the chemistry modeling, although noncontinuum effects are again predicted at the stagnation point.