Ablation behavior of carbon/carbon thermal protection structures with directional heat transfer

Efficient thermal protection of high-temperature stagnation regions remains a critical challenge for reusable hypersonic vehicles. In this study, a carbon/carbon (C/C) composite thermal protection structure with guided heat transfer is developed, in which directional heat transfer is realized by embedding high-conductivity carbon fiber bundles along the designed downstream direction. Fiber diameter and placement distance are varied to adjust the conductive path, rather than by introducing material-composition gradients, fiber-spacing gradients, or additional channels. A pore-scale coupled thermal-ablation model is established using MRT-LBM for macroscopic flow and SRT-LBM for heat conduction and pyrolysis gas diffusion, coupled with pyrolysis kinetics and a volume-fraction-based ablation scheme. The effects of Mach number, fiber diameter, and fiber placement on residual matrix fraction, average matrix temperature, and ablation morphology are investigated. The results show that directional heat transfer has a stage-dependent effect: it redistributes heat downstream and suppresses matrix ablation in the early stage, but heat accumulation within the fibers may accelerate local ablation later. Increasing fiber diameter enhances directional conduction and delays the transition at which fibers act as local heat sources, whereas forward fiber placement further mitigates ablation and helps maintain carbon matrix morphology. These findings provide theoretical guidance for designing high-performance C/C thermal protection structures.