Multidimensional Numerical Analysis of the Thermal Behavior and Pyrolysis Gas Flow Inside an Orthotropic Porous Material

This article describes a finite-volume fully implicit solver that simulates the transient thermal response and pyrolysis gas transport inside orthotropic charring ablators. Due to surface recession of ablators in the aeroheating environments, an arbitrary Lagrangian-Eulerian (ALE) formulation of the problem is presented. The governing equations (which consist of solid phase continuity, gas phase continuity, unsteady form of Darcy's law as gas momentum, and gas-solid mixture energy) are solved with an unstructured moving grid system. The boundary condition at the ablated surface is characterized by integrating the equilibrium thermochemical tables into the surface energy balance under assumption of a unity Lewis number. The developed computational scheme is verified using both analytical solution and code-to-code comparison. The simulations are performed on both cylindrical and iso-q shaped samples. The results show that the pyrolysis gas movement significantly influences the thermal response of the ablator. As the hot pyrolysis gas travels inside the porous ablator, it carries a great deal of energy, which enhances the solid temperature in the downstream region. Also, blowing the gas into the freestream has reduced the net convective heat flux, resulted in a decrease in the heat penetration area inside the ablator and char depth in the vicinity of permeable boundaries.