Aerothermodynamic analysis of high-altitude space launcher with direct-simulation Monte Carlo method

Aerothermodynamics of space launchers operating at high altitudes (above 100 km) is characterized by complex physical processes that are related to the substantially higher air rarefaction with respect to lower altitudes. Consequently, the use of continuum methods to numerically simulate such flow conditions is questionable. In this study, the problem of proper assessment of the aerothermodynamic behavior of space launchers operating at high altitudes is analyzed considering Vega in its ascent flight, an actual space launcher that has already performed a number of successful flights. The direct simulation Monte Carlo molecular method is used to carry out the simulations. After a convergence analysis of the adopted numerical approach, a comparison of different air models is presented to highlight the effect of chemical reactions and molecules vibrational excitation. Then, a comparison of the flowfield around the Vega launcher is reported at two altitudes (113 and 127 km), where the third stage of the space launcher is not propelled. The analysis describes the effects of the atmospheric air rarefaction, which has significant repercussions on the bow-shock structure and the drag coefficient. Finally, the achieved solutions are compared with computational fluid dynamics (CFD) continuum solutions to show that a standard CFD approach is not able to represent the physical phenomenon under examination, due to the model’s breakdown caused by the effects of rarefaction.