High speed civil transport has become a promising field with the development of globalization. It can dramatically shorten the time of international travel. However, high speed civil transport needs to meet several performance, environmental, and economical requirements. The propulsion system is one of the keys to satisfy these severe requirements. One critical requirement for the propulsion system is achieving great performance during the subsonic cruising condition and supersonic cruising condition. It is difficult for traditional gas turbine engines, such as turbojet and turbofan, to meet this performance requirement. The turbojet can produce high speed exhaust, which is beneficial for the supersonic cruising condition. However, high speed exhaust can lead to high energy loss during the subsonic cruising condition, which causes the high fuel consumption of turbojet. The turbofan can produce lower speed exhaust due to the splitting of bypass duct, which is beneficial for the subsonic cruising condition. However, low speed exhaust can lead to the deficiency of thrust during the supersonic cruising condition. Therefore, novel engine types are presented to meet this severe performance requirement. Variable cycle engine is one novel gas turbine engine type that combines the feature of turbojet and turbofan. It contains many variable geometry components. Through the combined adjustment of these components, the engine bypass ratio can be adjusted within a wide range. During the subsonic cruising condition, it can operate with high bypass ratio to reduce fuel consumption. During the supersonic cruising condition, it can operate with low bypass ratio to produce high thrust.

The configuration of variable cycle engine for high speed civil aircraft has not been determined. It is still a problem that what the performance benefits of different engine configurations are. In this article, two potential variable cycle engine concepts were studied and compared. Both of these two engines have two bypass ducts. One engine consists of a conventional core engine and a sophisticated fan system. The other engine consists of a novel core engine and a conventional fan system. Firstly, the cycle parameter design was conducted, which involved the pressure ratio, bypass ratio, and so on. It presented the principle of cycle parameter determination for the civil aircraft with wide speed range. Secondly, the control law of variable geometry components was studied to fulfill the potential of engine during subsonic cruising and supersonic cruising. The matching mechanism of components was also analyzed at this stage. Finally, the performance of these two engines were compared. The performance benefits and technical risk of each engine were presented in this section. This study is helpful to understand the impact of different engine configuration on the engine performance. It can also offer reference for the high speed civil aircraft propulsion system design.


A Study of Two Variable Cycle Engine Concepts for High Speed Civil Aircraft

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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