Optimization of Variable Cycle Engine Throttle Schedules Using Gradient-Free Methods

Abstract The variable cycle engine (VCE) represents a significant advancement in jet propulsion technology by offering enhanced operational flexibility through the integration of variable geometries within the engine's flow path. Key features, such as adjustable compressor inlet guide vanes (IGVs) and variable area bypass injectors (VABIs), enable the engine to dynamically adapt to varying flight conditions. These adaptations optimize engine performance across a broad range of flight regimes, including both subsonic and supersonic speeds. This capability is particularly advantageous for civil supersonic transport, which requires efficient operation at subsonic speeds over populated areas. It is equally beneficial in defense applications, where engines must deliver high specific thrust during maneuvers such as dogfights or interceptions while also supporting extended subsonic loitering. Furthermore, the VCE's ability to maintain constant airflow at lower throttle settings offers unique opportunities for improved thermal and power management. However, the increased operational flexibility of VCEs comes at the cost of greater system complexity, introducing new challenges in engine performance analysis, control, and optimization. To address these challenges, this work employs a robust gradient-free optimization strategy to develop an engine throttle schedule that maximizes performance across a range of operating points (OPs) for a three-stream VCE. The results of this investigation show that a significant improvement in maximum thrust output can be achieved over the entire operational envelope. At partial throttle, a moderate reduction of specific fuel consumption (SFC) was observed.