Master thesis and internship[BR]- Master's thesis : Stagnation line aerothermochemistry. Focus on uncertainty quantification in nitrogen plasma-graphite interactions in VKI Plasmatron[BR]- Internship

Abstract

Entering or exiting the atmosphere of a celestial body is a challenging task. The interactions between a space-vehicle and the flow surrounding it create a strong detached wave. Complex Gas-Surface Interaction phenomena occur between the resulting chemically reacting boundary layer and the vehicle’s surface, causing strong heat fluxes and chemical reactions. Thermal Protection System (TPS) are designed to protect the spacecraft. A proper knowledge of the interactions between the flowfield and the surface of the TPS is fundamental for the design of this part of the vehicle. In this essay, uncertainty quantification techniques are used to study the interac- tions between nitrogen plasma and TPS’s of carbonaceous materials. Two test- ing campaigns, one at lower pressure (15 hPa) and one at higher ones (100, 200 hPa), performed in the Plasmatron, a high enthalpy facility in the von Karman Institute, are analysed with the aim of comparing the Nitrogen-Carbon ablation models proposed by Prata and the modified version suggested by Capriati. During the experiments a plasma of Nitrogen interacts with a hemispherical graphite sample. Indirect uncertainties on the blowing mass flow rates for the different test cases are analytically quantified. A computational tool developed at the von Karman Institute is used to simulate the flowfield along the stagnation line. Faster propagation of the uncertainties is achieved using surrogate models. Neu- ral Networks and Kriging models are analysed. The comparison between the uncertainties on the experimental results and the numerical propagation of the uncertainties on the experimental conditions of the tests using the two abla- tion models coupled with the Stagline solver shows that the model proposed by Capriati improves the predictions at low pressures (15hPa), whereas Prata’s ab- lation model is bis more accurate at higher pressure campaign (100hPa, 200hPa). None of the two ablation models seems to well capture the pressure-dependence of the reactions; a further calibration of the model is then suggested to improve model predictions over the entire pressure range.