Detached eddy simulation of Callisto vehicle during subsonic retro-propulsion descent

Abstract

The estimation of aerothermal loads along the trajectory are a design driving factor during launcher development both for expendable as well as reusable space launch systems. The thermal loads directly influence TPS design and the fore the vehicle mass and mission performance. For reusable launch vehicles (RLV) (e.g. Falcon9, Spaceship) the thermal loads and the selected TPS materials might have direct impact on the refurbishment effort and concurrent launch cost. For the CALLISTO vehicle the highest heat fluxes are mainly during the subsonic retro-propulsion phase due to heating from hot exhaust gases and heated air in proximity of the aft bay and on the exposed structures like legs and fins. In the presented study we conducted computational fluid dynamics (CFD) study using the Detached Eddy Simulation (DES) approach in order to determine the unsteady and time-averaged aerothermal loads on the vehicle at beginning of the demo flight powered descent at M=0.8. The study was conducted for 0.3 s of flow time after the start up period. Subsequently the time-averaged loads were evaluated and compared to the baseline RANS model for the different vehicle interfaces. Based on the simulation results it can be observed that there are (1) clear differences between RANS and DES for plume core length, (2) strong loads fluctuations (aerodynamic and thermal) due to large scale turbulent structures in the plume but also (3) that the qualitative loads distribution is similar in average when compared to the RANS results. While large scale turbulent structures heavily influence the instantaneous thermal loads on the different vehicle interfaces the time-averaged results show a qualitative similar distribution to the RANS results for the same conditions. However the impact of the higher instantaneous loads may strongly depend on the material properties and the thermal mass of the underlying structure and the TPS system.