Performance Enhancement of Subsonic Turbofans 2016-01-2018
The key commercial aircraft propulsion requirements toward ensuring flight safety, operational efficiency, reduced CO2 footprint, and community acceptability include high installed thrust, low specific fuel consumption, and reduced noise. The objective of this paper is to highlight the various ways turbofan performance can be enhanced. First the advantage of high bypass ratio (BPR) configurations will be explained with the help of clean sheet cycle designs with the corresponding off-design performance. The achievement of hot day performance and improved durability with high BPR designs, and the benefit from core supercharging has been presented. Next, the use of on-line control effector modulations, including variable bypass exhaust nozzle, for further improvement in cruise SFC (up to an indicated 2.6%) is shown. This is followed by a discussion of medium BPR mixed exhaust designs which have a performance advantage compared to the same BPR separate exhaust configurations. Additionally, a patented concept of an integrated ejector/turbofan/nacelle configuration which increased installed net thrust at altitude by more than 10% is discussed. The ejector suction pulled through a perforated nacelle significantly reduced nacelle drag, contributing to increased installed thrust, as evident from the presented CFD results. This concept has the additional benefits of reduced noise from dramatically lower jet velocity as well as increased gross thrust at sea level take-off. The ejector thrust augmentation at take-off could potentially reduce the size of the basic engine.