An implicit coupling framework for numerical simulations between hypersonic nonequilibrium flows and charring material thermal response in the presence of ablation

Abstract: An implicit coupling framework between hypersonic nonequilibrium flows and material thermal response is proposed for the numerical simulation of ablative thermal protection materials during its flight trajectory. Charring ablative materials, when subjected to aerodynamic heating from hypersonic flows, undergo complex processes such as ablation and pyrolysis, involving heterogeneous and homogeneous chemical reactions. These multi-physical phenomena are simulated by a multicomponent material thermal response (MTR) solver that takes into account the complexity of component of pyrolysis gases. The species concentrations are calculated to improve the accuracy of transport and thermophysical parameters of pyrolysis gases. The MTR solver implements implicit time integration on finite difference discretization form to achieve higher efficiency. The numerical solutions of hypersonic flows and material thermal response are coupled through a gas-surface interaction interface based on surface mass and energy balance on the ablating surface. The coupled simulation employs the dual time-step technique, which introduces pseudo time step to improve temporal accuracy. The explicit coupling mechanism updates the interfacial quantities at physical time steps, which achieves higher computational efficiency, but introduces time discretization errors and numerical oscillations of interfacial quantities. In contrast, the implicit coupling mechanism updates the interfacial quantities at pseudo time steps, which reduces the temporal discretization error and suppresses numerical oscillations, but is less efficient. In addition, a simplified ablation boundary based on steady-state ablation assumption or radiation-equilibrium assumption is proposed to approximate solid heat conduction without coupling the MTR solution, providing quasi-steady flow solutions in the presence of ablation.