Aerothermodynamic study of UHTC-based thermal protection systems

Computational Fluid Dynamics (CFD) simulations are coupled to a thermal analysis model to investigate the thermal response of the new Ultra High Temperature Ceramics (UHTC) being considered for Thermal Protection Systems (TPS) of future reusable re-entry vehicles. The numerical methodology has been applied to the Sub-orbital Re-entry Test (SRT), mission foreseen in the frame of the Italian unmanned space program. The numerical prediction of the aerodynamic heating of the sharp nose of the vehicle has been performed coupling the solution of the external aerodynamic flow field with the thermal field in the TPS; different methodologies have been applied, considering the effects of surface catalysis and laminar-turbulent transition. The results indicate that, for a correct prediction of the aerothermal loads on a UHTC material, coupled time-dependent simulations for both external aerodynamic flow and internal thermal field are essential. The numerical investigations also show that surface catalysis is of negligible importance for a sharp configuration in free flight, but it must be taken into account while performing ground tests in high enthalpy facilities. Furthermore, for the considered sharp configuration, laminar-turbulence transition effects are critical for TPS design, since they may increase TPS surface temperature of, at least, 400 K. (c) 2005 Elsevier SAS. All rights reserved.