Catalytic characterization in plasma wind tunnels under the influence of gaseous recombination

Abstract

The catalytic properties of materials used in re-usable thermal protection systems (TPSs) of re-entry vehicles are mainly characterized in plasma wind tunnels. These facilities are adequate to reproduce the thermo-chemical environment found in hypersonic flights. Catalytic recombination coefficients (W) determined empirically for the TPS design process are used to validate catalytic models. Recent experiments in plasma wind tunnels present some contradictions with current catalytic models used in computational fluid dynamics simulations. This work explores the coupling between homogeneous and heterogeneous reactions and its influence on the heat flux measurements, in order to explain such contradictions. For that, three copper calorimeters (at 350 K) are inserted in probes of different sizes, and they are tested in the Plasmatron facility at the von Karman Institute under different chemical regimes, which are modified by the probe diameter. A dimensional analysis of the acquired data based on previous non-equilibrium boundary formulations shows that an empirical recombination coefficient can be falsified by the presence of homogeneous reactions. Then, in the framework for the post-flight analysis of the European Space Agency's intermediate experimental vehicle, the local heat transfer simulations methodology is applied under peak heating conditions. A new probe is designed, manufactured, and tested in the Plasmatron to measure the recombination coefficient on C/SiC under the closest flow conditions with respect to the flight.