Carbon-Carbon Ablation Experiments in the Sandia Hypersonic Shock Tunnel

Results of an experimental investigation into the ablation of carbon-carbon material samples in the Hypersonic Shock Tunnel at Sandia National Laboratories are presented. Commercial-off-the-shelf carbon/carbon billet was acquired and machined into flat samples to be inserted on the wedge-face of a 45◦ half-wedge model. The samples were clamped at two ends by copper electrodes and connected to a high-power DC power supply to resistively heat them to about 2000 K before the experiment. High-speed imaging of the sample response during the experiment allowed us to observe spallation at the material surface while 50 kHz tunable diode laser absorption spectroscopy monitored the temperature and number density of carbon monoxide in the flow aft of the sample. Two different surface temperatures of the carbon/carbon samples were investigated in this work: a high temperature condition at about 2200 K and a lower temperature condition at about 1900 K. These temperatures were chosen to explore the sensitivity of oxidation rate to temperature while staying well below the sublimation temperature of carbon. Additionally, two different flow conditions were explored: a 2.7 km/s freestream velocity condition with a bulk enthalpy of about 3.8 MJ/kg and a 4.2 km/s freestream velocity condition with a bulk enthalpy of about 10.4 MJ/kg.