In certain applications, different regions of the computational domain experience flow conditions that are so different that it is very difficult for a single solver to produce accurate results at the extremes. In many situations, such problems can be separated and solved using loosely coupled solvers. Each solver is chosen to provide highly accurate solutions for the prevailing flow conditions. 

ESI's CFD-FASTRAN, a compressible flow solver, is ideally suited for high speed external aerodynamics problems and the multi-physics solver CFD-ACE+ is ideally suited for heat transfer problems involving conduction, convection (natural and forced) and radiation. 

 A large amount of aerodynamic heating is generated over hypersonic vehicles during re-entry. Thermal Protection System (TPS) materials are employed to prevent the heating from conducting into the internal cabin, which holds electronic devices, passengers and other vital components. As a time-dependent process, the material making up TPS is at a low temperature and “soaks up” the heat – the conductivity of the material transports the heat (from the vehicle surface) through the thickness. The material will also re-radiate some of the heat back to the flow – the amount depending on the emissivity of the material. A primary concern is to estimate the effects of aeroheating on the internal volume of the capsule and its effect on electronic devices, passengers and cooling systems. In this application, typically the external flow is hypersonic in nature, whereas the flow within the capsule is a very low speed flow dominated by natural convection. In addition, to hypersonic aerodynamic heating, several other physics including heat conduction, natural convection and radiation has to be accurately modeled. CFD-FASTRAN solves for the external hypersonic flow and CFD-ACE+ solves for heat conduction, convection and radiation. Exchange of heat flux/temperature data between FASTRAN and ACE occurs at defined interfaces.