Earth re-entry capsule CFD simulations taking into account surface roughness and mass injection at the wall

Abstract

Future space exploration missions will likely use capsule type ballistic re-entry vehicles that will re-enter the earth atmosphere at very high speed (velocities in the order of 11.7 km/s or higher, this compared to 7.5 km/s for the US Space Shuttle). Passive concepts will be employed for the deceleration, and the thermal protection system (TPS) needs to be dimensioned to protect the vehicle and samples from the effects of the aerodynamic heating. The technology readiness level of these passive concepts is today still rather low, leading to large design margins. This paper is concerned with the design of a possible earth re-entry capsule, it discusses the re-entry trajectory and heat loads encountered during descent. Detailed CFD simulations were made for three selected points on the re-entry trajectory. The ablation of the TPS material was taken into account through a mass injection boundary condition. The turbulence models employed in the study were modified to account for surface roughness due to ablation. Calculated heat fluxes and shear stresses for a smooth wall are compared with results from empirical correlations and showed a fairly good agreement. For rough walls, the CFD results show a substantial increase in convective heat flux, while the injection of mass at the wall reduces the convective heat flux.