Oxidation Response of Transpiration-Cooled ZrB2 on a Hypersonic Stagnation Point

This work presents the oxidation response of a transpiration-cooled hypersonic stagnation point made of porous ZrB2. Low-order models are used to calculate the surface temperature and oxygen concentration for a given flight condition. An analytical material oxidation model computes the surface recession and oxide layer thickness. A 500 s steady-state trajectory at 44 km altitude and 3.6 km/s velocity is found to lead to 2.2 mm recession of the 3 mm nose radius. A constant mass injection at a blowing parameter of 0.6 reduces the recession to just 0.21 mm. The displacement of freestream oxygen by transpiration cooling has a significant effect on oxidation. Not accounting for the displacement of oxygen at the surface would increase the recession by up to 197%. The recession along the transient trajectory of an envisioned hypersonic vehicle with a 3 mm nose radius is found to exceed 0.94 mm with no mass injection. It is shown that nitrogen and helium injection at a blowing parameter of 0.6 can reduce the recession to 0.13 and 0.075 mm, respectively.