Numerical Study on the Thermal Loads During a Supersonic Rocket Retropropulsion Maneuver

The return and vertical landing of the first launch stage is a concept enabling reusable launch systems and has been successfully applied by SpaceX with the Falcon 9. The Falcon 9 first stage descends by two or three phases of retropropulsion. Especially the supersonic retropropulsion phase, using three of its nine engines, is of interest because it exhibits conditions close to Mars reentry. During retropropulsion, the first stage is partially submerged in the hot exhaust plume. In this study, a generic model based on the Falcon 9's features and dimensions is used to perform a numerical investigation of the plume–vehicle interaction. Using large-eddy simulation and Reynolds-averaged Navier–Stokes equations (RANS)-based computational methods, the flowfield is characterized at different trajectory points during retropropulsion. Based on several steady RANS calculations, an aerothermal database is created and coupled into a simple finite element structural heating model of the casing. The results show that, despite the high gas temperatures, the low gas density leads to a manageable heat flux and only a moderate temperature increase on the cylindrical walls when using conventional aluminum materials.