CAE Blog

In certain applications, different regions of the computational domain experience flow conditions that are so different that it is very difficult for any solver to produce sufficiently accurate results at the limits. 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 regimes. This kind of flexibility and fidelity is necessary when users are moving towards simulation-driven design solutions.

ESI’s CFD-FASTRAN, a compressible flow solver, is ideally suited for high-speed external aerodynamics problems while the multi-physics solver CFD-ACE+ is best for heat transfer problems involving conduction, convection (natural and forced) and radiation. Several users may already be aware of FASTRAN/ACE+ coupling for fluid-structure interaction (FSI) simulations. From v2009.2, users can take advantage of a new FASTRAN/ACE+ coupling for heat transfer simulations. A typical application example (see figure 1 below) on thermal environment simulation is presented to help you get started on applications where you can use this feature.



Figure 1.  Re-entry capsule at angle of attack. Mach number contours are displayed for the external flow;
internal flow is represented by velocity vectors; capsule thickness and internal component show temperature distribution.

A large amount of aerodynamic heating is generated over hypersonic vehicles during re-entry. Thermal Protection System (TPS) materials are employed to prevent the heat 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 and into the internal volume. The material will also 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 have to be accurately modeled. CFD-FASTRAN solves for the external hypersonic flow and CFD-ACE+ solves for internal flow, heat conduction, convection and radiation. Exchange of heat flux/temperature data between the CFD-FASTRAN and CFD-ACE+ solvers occurs at defined interfaces. A simple demo case can be downloaded here.