Performance mechanisms of electric power assistance in multi-shaft hybrid propulsion for high-speed flight

For future high speed flight missions, power-assisted hybrid propulsion offers potential benefits in thrust reserve and fuel efficiency. However, most existing studies remain descriptive and lack systematic analysis of how electrical power acts through different component pathways. To address this gap, an Electric-Decoupled Multimode Supersonic Hybrid Turbofan engine (EDMS-HTF) is modeled in this work. Starting from two distinct power transfer modes, namely the LPT Offload Mode and the Fan Augmentation Mode, the coupled aerodynamic, thermodynamic, and electrical interactions within the system are examined to reveal their respective performance mechanisms. Results show that in the LPT Offload Mode, external electrical power improves the core-cycle efficiency, while the feasible rotational speed range becomes significantly narrower at high power due to combined isopower and flow-limit constraints, leading to nonlinear thrust variation. In the Fan Augmentation Mode, electrical power directly drives the fan, modifying pressure ratio and mass flow distribution so that thrust increases monotonically with supplementary power-producing up to 13.9% improvement at takeoff and 34.5% under Mach 1.5 and 9 km conditions. When equivalent fuel consumption for power generation is included, the Fan Augmentation Mode achieves superior combined thrust-fuel performance across the full mission profile, whereas the LPT Offload Mode exhibits noticeable fuel consumption reduction only at high ground power levels. This study clarifies the energy transfer characteristics and performance constraints of alternative electrical-assist pathways in multi-shaft hybrid propulsion, providing a mechanistic foundation for future power allocation strategies and mission adaptive design of electrically assisted turbofan systems.