Technique development for investigation of axisymmetric graphite sample oxidation in hypersonic flow

Technique development for investigation of axisymmetric
graphite sample oxidation in hypersonic flow

Characteristics of graphite performance in a hypersonic blunt-body flow have been assessed experimentally and through simulation to determine mass loss. A 50 mm diameter graphite disc was heated from the downstream side with a plasma to approximately 2500 K, and then exposed to a cold Mach 4.5 flow. The disc was mounted on an experimental probe which was very similar to the European standard probe, normal to the flow. Surface temperatures were measured in the experiment using a correlation of the red pixel count of a high-speed camera, calibrated with a spectrometer.

The analysis shows that numerical simulation of the oxidation rate produced results that were within 50% of the mass loss measurements. Simulations indicate that oxidation through surface reactions producing CO was the major contributor to the ablation losses. Analysis involving comparisons between the experiments and simulations suggests that mechanical actions of the ablation process are only minor contributors to mass loss. The experiments show a significant spatial variation in thickness loss for the graphite test material over the disc radius though the spatial variation was still largely axisymmetric.

A new technique for preheating axisymmetric samples of heat shield material has been demonstrated through this work. Future applications for the technique are expected to be found in expansion tube facilities that can simulate the true flow energy under re-entry conditions.