Thermal Barrier Design of γ-TiAl Functionally Gradient Materials (FGMs) for Scramjet Engine Applications

Abstract

The work reported herein describes the results of analytical design using thermal-barrier-type Functionally Gradient Material (FGM) to insulate Scramjet cooling structures. Heat transfer coefficient of coolant side of the FGM (h_l), representing the mass of the coolant required to cool the main structure, and the thermal resistance parameter (t_FGM/λ_FGM) for equations governing the heat transfer at steady state were determined as the objective function and design variables, respectively. Using the function and variables, heat transfer of the gas-FGM-coolant was numerically analyzed for a stabilized ZrO₂/γ-TiAl FGM with a γ-TiAl cooling structure. The effective thermal conductivity (λ_FGM) for the stabilized ZrO₂/γ-TiAl FGM was calculated from the temperatures of the heated and cooled surfaces of the FGM, and from the enthalpy difference of the coolant at the inlet and outlet manifolds of the cooling structure, which was measured utilizing the Xe are lamp heating test. Then the optimum t_FGM-λ_FGM was found to be largely dependent upon the resistant temperatures of the high temperature and low temperature side materials of the FGM. In the cooling structure using ZrO₂/γ-TiAl FGM with optimized thermal resistance parameters (t_FGM/λ_FGM), the mass of coolant required to maintain the γ-TiAl cooling structure at temperatures below its resistant range was 35% of that of the cooling structure without FGM.