Evaluation of a Mixed Flow Turbofan Engine with Intermediate Turbine Burning for a Supersonic Aircraft 2007-01-3932

The requirements for high performance military aircraft include air superiority, interception, interdiction and close air support. The optimization of a power plant to meet the needs for each of these missions requires the evaluation of the system as a whole with engine size and performance obviously being a very important part of the evaluation. No single engine concept can optimally meet the needs of these different mission requirements, but practical cost considerations has historically required military fighter aircraft to operate in multi-mission roles. Of the four missions, air-superiority and interception require operation at supersonic speeds and the possible use of thrust augmentation. Interdiction may also require high speed, but not necessarily supersonic speeds, and close air support requires only subsonic flight speeds.

The most widely used engine currently being used for the air-superiority, interception and interdiction missions is the low bypass ratio, high fan pressure ratio turbofan engine with an afterburner. A non-afterburning supersonic cruise requirement is part of air-superiority to arrive quickly on station, but the actual combat most likely occurs at medium to high subsonic Mach numbers with short periods of afterburner thrust during aerial combat. Requirements for interception are leading to an ever increasing need for high speed, as high as Mach 3, to achieve interception as quickly as possible. The turbofan engine is far from an optimized engine cycle for this mission, and the non-afterburning turbojet engine is a consideration. A ramjet would be desirable at high Mach, but it would have to be coupled as a turbine engine/ramjet hybrid to perform at low speed climb and acceleration.

An alternative turbine engine solution evaluated in this study is the turbofan engine with inter-turbine burning (ITB), which offers the benefit of complete combustion in a smaller, lighter package when compared with the afterburning turbofan. This study makes a direct comparison of the ITB engine with the turbofan engine for the air-superiority mission and with the turbojet engine for the interception mission.