Advanced Ablation Characterization and Modelling

Kurzfassung

Ablative thermal protection materials are a key technology for current and future space exploration missions. However, the mission feasibility is determined by the materials available, and the development of new materials is performed, essentially, by an iterative trial-and-error process. This is due to the absence of validated predictive models for ablative material behaviour. Models are tuned to bulk material properties from tests. In order to describe physical processes of the ablation correctly, the European FP7 project ABLAMOD with the partner organizations DLR, Airbus Defence&Space, Avio, Amoroim, Fluid Gravity Engineering, AIT, OGI, CIRA, VKI and University of Strathclyde has been formed. The main objective of the ABLAMOD project is to make a substantial step towards a predictive model of an ablative thermal protection system by incorporating aspects of high fidelity mesoscale ablator physics within a modular framework. In order to successfully develop such physics modules, the understanding of the fundamental processes occurring within the ablative materials must be improved. To this end, three major ablation materials, i.e. carbon based, silicon based and cork based ablators, need to be tested in well characterized long duration high enthalpy facilities using both standard instrumentation and advanced measurement techniques. These advanced spectroscopic techniques lead to a significant improvement in the detailed characterisation of the material behaviour at the mesoscale level. Both virgin and char versions of the materials have been thermally characterized and the internal structure has been scanned by means of Computer Tomography (CT). In parallel using the state-of-the-art knowledge of ablator physical processes, modules for the specific phenomena like internal gas flow, radiation, gas transport properties and gas-surface interaction have been developed. Computed Pitot pressure and heat flux profiles using simplified thermal non-equilibrium model show a good agreement with the experimental data in the arc heated facility L3K. The computer tomography data allowed studying the microstructure of all three ablator materials before and after charring. This data has been directly used for DSMC modelling. A high enthalpy flow field has been simulated using a Computational Fluid Dynamics (CFD) code. This simulation used updated transport properties of the gas. The results of numerical rebuilding of the thermal response of the carbon based ablation material using the ablation code FABL in combination with the new modules developed within the ABLAMOD project showed an improved agreement with experimental data.