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Four different thermal management concepts were investigated in order to improve the thermal protection capabilities for future reusable space vehicles during atmospheric entry and for hypersonic transport vehicles during flight. In a first step, the requirements for thermal management were compiled for future missions. Based on the assessments a wing leading edge was defined as the baseline configuration for THOR. Specific reference configurations were defined which implement the key elements of the considered thermal management concepts into a leading edge geometry. For the considered thermal management concepts the physical potential for improvement was checked a priori based on existing measured data or simulations using appropriate models. In the conceptual of the project, the configurations were refined with particular focus to experimental concept verification in high enthalpy facilities. Convenient test configurations were identified for the arc-heated facility L3K and the shock tunnel HIEST.
In preparation of experimental verification, manufacturing of the ceramic materials and structures as well as their integration into the test assemblies were associated with several challenges. New processing routes were found for the production of large CMC parts with integrated highly conductive fibres. A newly developed replica technique starting from 3D-printed polymeric templates was developed for the preparation of SiC-based ceramic lattices. Appropriate joining techniques were established for the bonding between lattice and solid CMC. Structures for transpiration cooling were transferred to smaller scale by a new integration technique for porous materials based on electroplating. Manufacturing tasks were accompanied and supported by material characterization activities, which primarily focussed on the newly developed materials and high temperature joining techniques.
Leading edge test assemblies were prepared for experimental verification in L3K. The tests were carried out as transient tests to steady-state conditions. Temperature measurements were used to assess the thermal performance with particular consideration of thermal equilibration and reduction of the stagnation temperature. Thermal equilibration was observed mainly for the two passive cooling concepts. In particular, the opening of a small cavity at the nose with concept 1b resulted in a significant settlement of temperatures differences. Comparable temperature reductions were evaluated for the two passive concepts and the active concept 2a, all between 70 K and 80 K. By combining the two passive concepts, the temperature reduction could be enhanced to more than 100 K, allowing the material to sustain an additional heat load of more than 20% of the reference load. These results were verified by numerical rebuilding using coupled simulations.
For transpiration cooling, the interference of the emanating gas with the boundary layer, was investigated in the test campaign in the HIEST shock tunnel. At low Reynolds number conditions effective cooling was verified, but with increasing coolant flow rate the risk of boundary layer transition was found enhanced. This result was confirmed by numerical rebuilding as well.
Eventually, improvements to thermal management capabilities were verified for all four considered concepts. Experimental verifications tests indicated considerable reductions of stagnation temperatures the leading edge test configurations. These reductions are correlated with a potential to increase the applicable heat loads considerably. The experimental results confirm a TRL level of 2-3 for each concept. In addition, the investigations indicated potential for technical and methodical optimization. Accordingly, the evaluated improvements might be increased further.