Non-Intrusive Multidimensional Investigation of Spallation Phenomena in Ablating Materials

• Applicant: Dr.-Ing. Stefan Löhle, since 6/2018
• Subject Area: Fluid Mechanics
• Term: from 2017 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 329878198

This study is a multidimensional experimental investigation into the spallation phenomena for spacecraft thermal protection materials. Spallation is an important, yet poorly understood, component of the ablation process which provides thermal protection for a spacecraft entering a planetary atmosphere ensuring flight and mission success. Thus far there is only a very limited amount of experimental spallation data available in the literature, and the data which is available is not particularly detailed.The objective of this work is to, for the first time, collate extensive experimental measurements targetting spallation and to quantify the effects of spallation on spacecraft thermal loading. This is split into two components, firstly the surface state of the material and the spallation particles ejected from the surface will be characterised, and secondly, the effect of these particles on the overall flow field will be evaluated.A detailed investigation of the surface state will be conducted using two-colour ratio pyrometry, photogrammetry, tomography and high-speed imaging. This will result in the measurement of the number of particles spallated and the particle sizes, temperatures and velocities. The surface state measurements are critical for understanding the material response as this is heavily influenced by the surface temperature and the amount of material physically stripped from the surface. These measurements will allow the effect of the spallation process on the overall ablation and material response to be evaluated. Additionally, the ejected particle characteristics are key to the modelling of the effect of the spalled particles on the flow-field.The second component of this investigation is the experimental determination of the effect of the spalled particles on the overall flow-field. The particles are ejected by the spallation process and introduce new radiating and reacting components into the flow-field which have been historically ignored in ablation modelling. Utilising spectroscopy, high-speed filtered imaging and tomography this investigation will quantify the effect of these injected particles on the flow-field. The experiments will measure the radiation intensity modifications caused by the particles, both in terms of absolute radiation intensity and spatial distribution of the radiation.The data sets resulting from this investigation will be the first extensive and detailed measurements of the spallation phenomena. These data can then be used for verification and validation of material response codes and coupled ablation flow-field computational analyses. This can then improve the numerical models of spacecraft thermal protection materials ensuring higher certainty and efficiency in future spacecraft thermal heat shield design.

• DFG Programme: Research Grants
• Ehemaliger Antragsteller: Dr. Fabian Zander, until 5/2018