Plasma Wind Tunnel Testing of Ultra High Temperature Ceramics: Experiments And Numerical Correlation

Abstract

The thesis is focused on the aerothermodynamic and oxidation behaviour of ultra-high-temperature Ceramic (UHTC) for aerospace applications. UHTC are very high temperature resistant (>2000K) materials, with good chemical inertness and mechanical properties. These materials could be used for next generation aerospace and hypersonic vehicles. The arc jet plasma wind tunnel available at the Department of Aerospace Engineering of Naples (DIAS) is able to reproduce specific total enthalpies and stagnation pressure conditions typical of atmospheric re-entry vehicles; for this reason advanced materials for hypersonic applications can be investigated. In particular, the materials behaviour at ultra high temperatures, the durability at repeated warmed up, and oxidation resistance can be analysed. The experimental procedure based on the simultaneous use of an infrared thermocamera and a dual-colour optical pyrometer allowed to take accurate measurements of the real temperature surface distributions during tests and to evaluate the spectral surface emissivity, which is a fundamental property for aero-thermal heating. Numerical models allow the simulation of the aerothermochemical and flow fields characterizing the details of the wind tunnel experiments. For example the heat flux, the chemical environment on the model, the aero-thermal heating, and the effects of the material properties on the thermal heating can be analysed in detail. The fundamental results obtained are: characterization of several UHTC models; they are original because specific properties of UHTC materials are provided for the first time. In particular the atomic recombination induced by surface catalyticity, the spectral emissivity, the oxidation behaviour and temperature resistance at temperatures in the order of 2000K. In addition, electronic micrographs and X-rays analysis of cross sections of the investigated UHTC samples after test, allowed to characterize the oxidation layer and explain the measured surface properties