Quantitative Comparison of Two Variable Cycle Engine Concepts

Variable Cycle Engines (VCEs) are a family of promising propulsion solutions for supersonic aircraft, applicable to both supersonic civil aviation and the defense sector. They offer the capability to adapt engine performance across a wide range of flight conditions and mission requirements. By modulating the internal flow path, VCEs can deliver high specific thrust during supercruise while maintaining fuel efficiency and lower noise levels during subsonic flight phases, such as takeoff and landing. The improved operational flexibility is especially valuable when conflicting performance requirements exist along the mission profile, where the adaptability can alleviate design trade-offs. However, by introducing variable geometries in the flow path, the complexity of the engine system increases, making the design and operation of the engine more challenging. This work quantitatively compares two VCE architectures, "Two-Bypass" and "Three-Stream" type, and a conventional mixed-flow baseline engine for a supersonic civil transport mission. The engine design is optimized using a multi-objective gradient-free optimization strategy that incorporates the design parameters and off-design control parameters within a single optimization loop. Special care is taken to include the intake installation effects in the form of spillage drag, which is crucial at these high flight Mach numbers.