LOW BPR TURBOFAN PERFORMANCE WITH POWER EXTRACTION

Paper in proceeding, 2022

Military aircraft require more electrical power than they used to do. The increased power consumption is due
to a transition from pneumatic and hydraulic systems to electrical and the introduction of new, more power
consuming equipment. This paper summarizes an engine performance study, performed with a modeled low
bypass ratio mixed flow turbofan engine, where power is extracted from the low-pressure shaft, the highpressure
shaft or a combination of the two. High-pressure shaft power extraction results in a considerable
turbine inlet temperature increase. If the operating point has sufficient margin to the maximum turbine inlet
temperature limit and if the power extraction is acceptable from an operability point of view, power can be
extracted from the high-pressure shaft without causing much penalty on engine thrust. If the engine is running
close to its maximum turbine inlet temperature, which is typically the case at low altitude and high aircraft
speed, power extraction from the low-pressure shaft could be a better alternative due to the lower turbine inlet
temperature increase. This gives a higher margin to the maximum turbine inlet temperature limit. However, if
the full potential of low-pressure shaft power extraction is to be utilized, the high-pressure compressor must
have some aerodynamic overspeed margin for the low-pressure shaft power extraction case. At part power,
the lower specific thrust of the low-pressure shaft extraction case compared to the high-pressure shaft power
extraction case, is favorable from a propulsive efficiency and fuel consumption perspective.