Numerical study on combined regeneration cooling of supercritical kerosene and supercritical CO₂ considering cracking effect

To meet the efficient heat transfer demand of thermal protection systems for hypersonic vehicles at extremely high thermal environment (Ma ≥ 8), this work numerically investigates the thermo-hydraulic characteristics of composite cooling of supercritical RP-3 kerosene pyrolysis and supercritical CO₂ regeneration cooling channels. Three channel sections (circular, triangular, rectangular) and two flow arrangements (co-current flow and counter flow) are studied. Based on the SST k-ω model and a 24-steps 18-components cracking reaction mechanism, the coupling rules of cracking reaction, flow behavior and heat transfer are systematically revealed. Compared with the single-kerosene baseline, the dual-fluid configuration suppresses the peak wall temperature by about 25–30%, and the sCO₂ side absorbs 39–49% of the total heat load. Counter-current flow yields higher local Nusselt numbers, whereas co-current flow gives lower and more uniform wall temperatures together with a higher cracking rate, revealing a trade-off between heat-transfer intensity, wall-temperature suppression and fuel conversion. The circular channel provides the best temperature uniformity and the highest overall performance index η that balances heat-transfer enhancement against flow-friction penalty. The combination of a circular section and co-current flow is found to be optimal. This study provides a reference for the structural design and optimized operation of active thermal protection systems for hypersonic aircraft.