Detailed Modeling of Cork-Phenolic Ablators in Preparation to the Post-Flight Analysis of the QARMAN Re-Entry CubeSat

The ever growing challenges faced in the field of space flight motivate the scientific community to seek innovative solutions. Considering that aerospace applications have a strong impact on several fields, a curious change in trend has recently started: space, so far inaccessible to most and reserved for government space agencies, is now capturing the attention of industrial companies, accelerating technical progress. The design of high-performance spacecraft, capable of operating in extreme environments, is thereby of primary interest. An incredibly challenging task is related to atmospheric entry and thermal protection issue, which require the development of special heat shields. Ablative materials are largely used with this aim and, in particular, a class of low-density, charring and cork-based ablators has been recently developed. In fact, the excellent properties of cork make it one of the best available solutions for these purposes. This master thesis project has been carried out at the von Karman Institute (VKI) for Fluid Dynamics, in Belgium, in collaboration with Cenaero. It deals with the analysis of the Cork P50, equipped on the QARMAN Re-entry CubeSat developed for ESA at VKI as a scientific demonstrator for Aerothermodynamic Research. Launched to the ISS on December 2019, the re-entry of QARMAN is estimated for August 2020 and the data collected during its re-entry will thus be used for validation purposes. The capability to model and predict the atypical behaviour of the new cork-based materials is considered a critical research topic, therefore this work is motivated by the need to develop a numerical model able to respond to this demand, in preparation to the post-flight analysis of QARMAN. The study is focused on the main thermal response phenomena of the cork P50: pyrolysis and swelling. Pyrolysis and, more generally, ablation have been analyzed by means of the multi-physics CFD code Argo, developed at Cenaero. Based on a unified flow-material solver, the Volume Averaged Navier-Stokes equations have been numerically solved to describe the interaction between a multi-species high-enthalpy flow and a reactive porous medium, by means of a high-order Discontinuous Galerkin Method. Specifically, a more accurate method to compute the pyrolysis production rate has been implemented. While the chemical composition of pyrolysis gases was pre-fixed so far, a routine calling the VKI MUTATION++ library has now been added, in order to compute the composition at equilibrium. A series of simulations has been performed, getting good results and highlighting the effect of the elemental composition, that should be estimated experimentally. The modeling of swelling represented the most ambitious task, requiring the development of a physical model accounting for this phenomenon, for the purpose of a future implementation within Argo. A 1D model has been proposed, mainly based on an a priori assumption on the swelling velocity and the resolution of a nonlinear convection equation, by means of a Finite Difference Method. Once developed, the model has been successfully tested through a Matlab code, showing that the approach is very promising and having thus opened the way to further developments.