radAblationFoam: A multi-field coupled ablation model considering in-depth radiation

Accurate prediction of the thermal response of semi-transparent ablative materials, such as Phenolic Impregnated Carbon Ablator (PICA), is critical for the design of thermal protection systems (TPS). However, traditional models often employ an effective thermal conductivity approach, neglecting the complex internal radiation transfer and its coupling with pyrolysis gas dynamics. This limitation leads to significant prediction errors under high-flux or short-wavelength irradiation. To address this, a multi-physics coupled solver, named radAblationFoam, is developed within the OpenFOAM framework. The solver integrates the Finite Volume Discrete Ordinates Method (FV-DOM) to solve the Radiative Transfer Equation (RTE), fully coupled with transient heat conduction, resin pyrolysis, and compressible gas flow in porous media. The model is validated against the Ablation Workshop benchmarks and laser heating experiments, successfully reproducing the wavelength-dependent charring depth that traditional models fail to capture. Numerical investigations on a 2D Iso-q geometry reveal that internal radiation significantly alters the thermal and mechanical states of the material. Specifically, a ‘radiation focusing effect’ is identified at the geometric corners, leading to a localized overlap of volumetric energy deposition. This phenomenon creates a subsurface high-pressure pocket (exceeding traditional predictions by over 10 kPa), which poses a severe risk of spallation. The study demonstrates that accounting for internal radiation is indispensable for the structural safety assessment of TPS components with complex geometries.