Experimental Investigation of Thermal Ablation by Melting in a Hypersonic Shock Tunnel

In this paper a novel approach for the experimental measurement of the ablation by melting is presented. The experiments are carried out with a hypersonic shock tunnel. The tested models are made of gallium, which melts at low temperatures, allowing the generation and then the measurement of the ablation profiles within only two milliseconds. By means of an optical visualization, the model surface changes are recorded during the experiment. An image post-processing algorithm computes the ablation profiles. The results for two hemisphere-cone models and one hemisphere-cylinder model in a Mach 4.5 nitrogen flow are presented. It is found that the maximum ablation occurs at an angular position of around 30 degrees off-axis rather than at the stagnation point. This is most likely a consequence of the laminar-turbulent transition on the model forebody