Two-dimensional study of charring ablative materials using finite volume method

Abstract

Numerical simulation of charring ablative materials using finite volume (F.V) method is presented in this paper and a new modeling approach for pyrolysis gas mass flux production for multi-dimensional analyses is proposed. Pyrolysis gas mass flux produced in carbon-phenolic ablation process is solved by a user defined transport equation. User defined functions (UDFs) are developed in FLUENT 6.3 to consider the equilibrium surface thermochemistry (EST) model of carbon ablation in air including the diffusion and sublimation. Source terms of energy and pyrolysis gas equations, temperature-dependent boundary conditions, material properties variations and wall recession are all implemented in these UDFs. Also, Spring-based smoothing method is utilized as the grid motion technique. Furthermore, one-dimensional (1D) thermal response of the stagnation point is investigated using a finite difference (F.D) FORTRAN code. To ensure the accuracy of the proposed multi-dimensional modeling, a comparison is made between the published data and the computational results achieved by 2D F.V method at the stagnation point and the 1D F.D outcome. It is found that the predictions for the centerline temperature rise in the 2D analysis is generally higher than those of the 1D code. Also, the maximum ablation mass flux and the maximum recession are smaller compared to 1D predictions. This approach provides an in-depth study of a charring material under heat loads in situations where the classical 1D approach fails, e.g. anisotropic materials, sharp geometries and insulator-backup material interface.