Variable Cycle Optimization for Supersonic Commercial Applications

Variable cycle engines (VCEs) hold promise as an enabling technology for supersonic business jet (SBJ) applications. Fuel consumption can potentially be minimized by modulating the engine cycle between the subsonic and supersonic phases of flight. The additional flexibility may also contribute toward meeting takeoff and landing noise and emissions requirements. Several different concepts have been and are currently being investigated to achieve variable cycle operation. The core-driven fan stage (CDFS) variable cycle engine is perhaps the most mature concept since an engine of this type flew in the USAF Advanced Tactical Fighter prototype program in the 1990s. Therefore, this type of VCE is of particular interest for potential commercial application.

To investigate the potential benefits of a CDFS variable cycle engine, a parametric model is developed using the NASA Numerical Propulsion System Simulation (NPSS). A procedure is developed to select a near-optimal engine cycle and power management schedules for the specified aircraft missions. The engine model is then incorporated along with a notional SBJ aircraft model into a system-level modeling and simulation environment to predict the aircraft performance. Both an all-supersonic cruise mission and a split subsonic/supersonic cruise mission are investigated. The VCE results are compared to those for a conventional mixed flow turbofan engine optimized for part power operations for each mission.