Final Report Summary - AEROSPACEPHYS (Multiphysics models and simulations for reacting and plasma flows applied to the space exploration program) Space exploration is one of the boldest and most exciting endeavors that humanity has undertaken and holds enormous promise for the future. After the successful manned missions to the Moon and many probe entries into the atmosphere of outer planets, our next challenges include bringing samples back to Earth by means of robotic missions, as well as continuing the manned space exploration program to send human beings to Mars and bring them home safely. Inaccurate prediction of the heat load on the surface of a spacecraft may be fatal for the crew or the success of robotic missions. Rocket scientists estimate this quantity during the design phase for the heat shield, which is used to protect payload and astronauts. To help them with this estimation, the AEROSPACEPHYS team has investigated the following mission killers: 1) Radiation of the hot dissociated plasma in front of the vehicle, 2) Complex degradation, or ablation, of the thermal protection material, 3) Flow transition from “smooth” laminar regime to turbulent regime. The PI and his team demonstrated that a poor understanding of the coupling between the radiation, ablation, and transition phenomena can lead to severe errors in the heat load prediction. To avoid space mission failure and ensure safety of the astronauts and payload, aerospace engineers resort to safety factors by increasing the heat shield thickness at the expense of reduced mass of embarked payload. Determination of safety factors relies on a discipline called uncertainty quantification that aims here at developing rigorous methods to characterize the impact of “limited knowledge” on the heat load. The design of the Apollo, Galileo and Huygens probes are famous examples of “lucky” heat shield design based on inaccurate simulations. A possible explanation is that the conventional physico-chemical models used for entry simulations are often stretched dangerously and used out of the validity range for which they have been conceived. Thinking out of the box and conducting basic research were thus necessary for advancements of the models that will define the environment and requirements for the design and safe operation of tomorrow’s space vehicles and planetary probes for the manned space exploration. Let us recall the three basic ingredients for predictive engineering: 1) Physico-chemical models, 2) Computational methods, 3) Experimental data. The team has integrated new advanced physico-chemical models and computational methods, based on a multidisciplinary approach developed together with engineers, chemists and applied mathematicians. One successful outcome of the AEROSPACEPHYS project was the development of a new software library called MUTATION++: MUlticomponent Thermodynamic And Transport properties for IONized gases written in C++. This library packages the state-of-the-art physico-chemical models, algorithms and data developed into a highly extensible and robust software designed to be coupled to simulation tools used by space agencies and industries. In particular, new physico-chemical models on the rotation-vibration energy transfer and dissociation of nitrogen molecules in atmospheric entry flows have been derived at the interface between computational chemistry and computational fluid dynamics. The AEROSPACEPHYS team and its collaborators have also developed multiphysics and multiscale numerical platforms interfaced to the MUTATION++ library to simulate planetary atmosphere entries, crucial to the new challenges of the manned space exploration program. The team pioneered the use of uncertainty quantification tools in aerospace applications for the prediction of flow transition from laminar to turbulent, as well as for model validation based on experimental data obtained in aerospace facilities. The research focused on the needs of the space agencies, benefitting from a long research experience at the host institution, the von Karman Institute for Fluid Dynamics, in supporting aerospace missions. In particular, a close collaboration with the aerospace industry led to the identification of intricate coupling mechanisms between the flow, radiation, and material fields allowing us to accurately predict the complex degradation of a new generation of low-density carbon-resin composite materials that will enable tomorrow’s space journeys.
