Trajectory-Scale Fluid–Thermal Analysis of a High-Speed Control Surface Gap

A framework is developed to enable high-fidelity, component-level, coupled fluid–thermal simulations over mission-scale trajectories. The framework integrates a custom solver that couples computational fluid dynamics (CFD) with finite element thermal analysis, while interfacing with a reduced-order thermal model to provide trajectory-dependent boundary conditions. The approach is applied to the fin–body gap region of a high-speed all-movable control surface over the course of a trajectory segment, where varying incoming boundary-layer characteristics are observed to shift gap-region flow structures with vehicle motion, driving movement of peak heating and temperature hot spots. Heating is amplified by up to [Formula: see text] relative to baseline conditions, with peak surface temperatures exceeding 2000 K. Additionally, two engineering-level prediction strategies are constructed and compared to the higher-fidelity coupled framework: one incorporating a single CFD solution and another neglecting CFD entirely. The former approach captures trends, and its root-mean-squared errors generally remain below [Formula: see text] in the thermal protection system and [Formula: see text] in the substructure, while the latter errors approach [Formula: see text] in the thermal protection system components.