A hybrid micro-continuum scale approach for predicting coupled thermal flow and heterogeneous chemical ablation process in porous media

Accurate prediction of the thermal response of ablative materials is crucial for ensuring the reliability of thermal protection systems (TPS). Ablative materials exhibit surface roughness due to material properties and manufacturing processes, which can consequently affect the transition behavior of the hypersonic boundary layer, heating rate, and skin friction of thermal protection system, etc. In this work, a hybrid micro-continuum scale approach for predicting coupled thermal flow and heterogeneous chemical ablation process in porous media is developed. The proposed model is validated through investigating the ablation process of carbon fibrous porous media under the high-temperature molecular oxygen flow. The effect of incoming flow Péclet number, porosity, and the initial pore-scale structure on the flow and thermal ablation process is further explored. The results show that during the ablation process, both high Pe number and high porosity lead to a greater ablation recession rate. Though different pore-scale structures in the porous media with same porosity exhibit almost identical average ablation rate, they can result in distinct disuniform velocity distributions within the porous media, which have a greater impact on ablation surface roughness. Under convective-dominated inflow conditions, it gradually forms a high-permeability “wormhole-like” pathway for the binary gradient porosity structure, leading to a maximum surface roughness. This proposed hybrid micro-continuum scale simulation method can potentially provide valuable pore-scale insights during the ablation of porous medium, enhancing the prediction accuracy of the material thermal response for TPS applications.