Numerical and experimental investigations on transpiration cooling

Abstract

Future challenges in aviation and space travel are closely linked to the development of propulsion engines. Enhancing the performance and reusability while reducing emissions increases the demands on the applied materials and cooling technology. In this context, transpiration cooling is of great interest, particularly if applied to lightweight composite materials. Within this thesis, a combined numerical and experimental approach has been followed to study transpiration cooling for CMC materials and more complex conditions. The research work focuses on experiments and the development of a numerical solver which was integrated into the OpenFOAM software package. The solver allows the simulation of complex transpiration-cooled structures in non-uniform sub- and supersonic hot gas flows. It is validated by means of comparisons to experiments which demonstrate good agreement for all test cases. First, the through-flow behaviour of C/C structures is investigated. The data suggests that the permeability coefficients are independent of the coolant gas used as well as temperature and pressure levels. Secondly, a subsonic turbulent channel flow with porous-wall injection has been simulated. The agreement of numerical boundary-layer profiles to measured data from literature validates the applied injection model for various coolant gases. The main part of the thesis then explores transpiration-cooled C/C structures in supersonic hot-gas flows. For this purpose, experiments in a wind tunnel have been conducted using flat and non-flat porous samples, a shock generator, and various coolants. Transpiration cooling significantly reduces the temperatures of the porous sample and the wake region. The effect depends on the blowing ratio as well as the coolant properties. Variations of the sample wall thickness yield locally increased coolant mass fluxes and intensified cooling. A similar effect was found for more complex main-flow conditions featuring shock waves and expansion fans.