SUMMARY

Future hypersonic cruise vehicles require sharp, shape stable Wing Leading Edges (WLE) with structural and thermal capabilities beyond the current state of the art. The concentrated aerodynamic heat flux on sharp leading edges leads to runaway thermal and mechanical failures. These vehicles may also experience intense accelerations in future military applications due to maneuvers or re-entry. Conventional, or wicked, heat pipes using liquid metal working fluids have been proposed as passive Thermal Protection Systems (TPS) since the 1970s, and have been shown to be feasible for speeds as high as Mach 8.
Recent research regarding oscillating heat pipes (OHPs) has highlighted potential advantages over wicked heat pipes including higher heat transport and improved performance in high acceleration environments. Additionally, the state of the art of refractory metal additive manufacturing is now capable of producing single part WLEs with good material properties.
In this work, two alternative heat pipe TPSs are explored to access the application of advancements in heat pipes and additive manufacturing. The systems feature tungsten casings and use gallium as a working fluid. The first alternative is a triangular micro heat pipe (MHP) based TPS that also includes magnetohydrodynamic (MHD) pumping. The second alternative system uses OHPs.
Preliminary analysis of the MHP-MHD system indicated the MHP pump design could not provide sufficient pressure to improve performance, while a system comprised of only MHPs could provide adequate cooling at high temperatures. The OHP TPS analysis indicated a maximum temperature below 2500 K could be sustained while traveling at Mach 10.5 at a 26.5 km elevation. Further research is required to determine the thermal-structural limits of the OHP based TPS and to assess the accuracy of the OHP modeling methods used for high temperature applications.