Diffusion flux modeling: Application to direct entry problems

Direct entry is a maneuver used by spacecraft that enter a planet's atmosphere without first orbiting the planet. Typical entry conditions involve high velocities in the range of 12 km/s and more. In contrast, the Space Shuttle reenters at velocities around 7.5 km/s. The high energy involved with an Earth direct entry causes the air to become completely dissociated and has a high degree of ionization compared to entries from Earth orbit. In this paper we compare the constant Lewis number Fickian diffusion method (CLN) to two multi-component models, the Self-Consistent Effective Binary Diffusion method (SCEBD) and the Stefan-Maxwell Iterative method (SM). The CLN method treats all species with the same diffusion coefficient, while the multi-component methods allow each species to have a separate diffusion coefficient that contributes to the overall diffusion. We have found that the multi-component methods give a lower surface heat flux and change other characteristics of the flow compared to the CLN method.