Analytical And Numerical Investigation Into Thermal Protection Mechanism Of Metallic Structural Heat Pipes In Hypersonic Vehicles

Hypersonic vehicles including ballistic missiles, cruise missiles, re-entry vehicles, trans-atmosphere aerospace aircrafts, etc. usually cruise in the atmosphere at a Mach number higher than 5. Developing hypersonic flight technology is extremely important for commercial and military applications. However, as the cruising speed of hypersonic vehicle has improved significantly, its service environment is even worse. Heat flux into the aircraft's leading edge (an extremely sharp local structure) is intense under a strong action of aerodynamic heating and this causes the temperature rising greatly and even leads to a failure of the material.In this thesis, a semi-active thermal protection scheme is presented by integrating a planner heat pipe into the structure of the leading edge. Then the thermal boundary conditions outside the leading edge are obtained from standard hypersonic correlations. Also theoretical analysis and numerical simulation are carried out respectively to predict the thermal protection mechanisms and cooling effects of this semi-active thermal protection scheme. Performance characteristics and feasibility of the heat pipe are assessed at specified flight conditions (Ma 6-8) with three different leading edge materials (nickel based alloy Inconel 625, niobium based alloy C-103 and molybdenum based alloy TZM).The analysis shows that isothermal temperature T_iso, maximum temperature T_max and maximum Mises thermal stressσ_eq in leading edge structure will increase greatly with a higher Mach number of the hypersonic vehicle. Under the hypersonic flight conditions in this work, the design length L has a strong influence on T_iso, T_max andσ_eq. T_iso and T_max will decrease rapidly, whileσ_eq will increase with a longer L. Also T_iso is independent from leading edge material, while T_max will decrease to some extent with increasing material conductivity, andσ_eq is sensitive to material mechanical property and temperature in the leading edge structure.The results also indicate that, if the high temperature heat pipe functions accordingly with lithium as the working fluid, the niobium alloy C-103 and molybdenum alloy TZM will meet the feasible requirements completely at Mach 6 to 8 with a 3mm leading edge radius and a 0.15m design length. While the maximum Mises thermal stressσ_eq will exceed the yield strength of Inconel 625 at a speed more than Mach 6, which means a failure.