Effects of thermochemical modelling and surface catalyticity on an Earth re-entry vehicle

Abstract

A numerical study has been conducted to assess the effects of thermochemical modelling and surface catalyticity on the design of a crew return vehicle re-entering from low Earth orbit. The effects of: complexity of chemical models, kinetics of reactions, vibrational relaxation, and wall reaction mechanism on vehicle aerothermodynamics and aerodynamics performances, and on some flowfield features, are highlighted. To this end, several numerical results derived for perfect and non-equilibrium reacting gas approximations are provided and compared. In this framework, a possible Earth-entry scenario for the proposed capsule-type vehicle is reported and extensively analysed by means of Navier–Stokes computations, performed both in trajectory-based and in space-based design approaches. Numerical results highlight that the accuracy of aerodynamic coefficients depends on the complexity of reaction mechanism considered in flowfield computations. For example, if the Zeldovich model is considered, the results produced are within 1 per cent of that of a solution with complete reaction mechanism, while the simulation speed up efficiency reaches about 40 per cent. This work underlines the fact that the CPU speed up depends, in particular, on the accuracy expected in vehicle pitching moment assessment, thus confirming that this parameter is one of the most critical vehicle aerodynamic performances to address in the case of a real gas-dominated flow. On the contrary, vehicle aerothermodynamic results show that, for a reliable heat flux evaluation, flowfield computations require a full reaction mechanism, as wall catalyticity plays a significant role when assessing vehicle aeroheating.