Exchange Rate Analysis for Ultra High Bypass Ratio Geared Turbofan Engines

This paper investigates the impact of thermal management methods on the design point and synthesis exchange rates of an ultra-high bypass ratio geared turbofan engine. In a typical thermal management system, where heat is managed by means of heat exchangers that transfer engine waste heat into oil, air, or fuel. However, the utilization of air–oil and fuel–oil heat exchangers has an adverse impact on engine performance. This paper investigates the impact on and engine’s specific fuel consumption and summarizes it into common exchange rates for different thermal management configurations. The results show that any pressure loss in the bypass duct results in a severe specific fuel consumption penalty (an increase of 1% pressure loss in the bypass duct causes a 2% specific fuel consumption increase at cruise conditions). In addition, quite severe is the impact of extracting air from the gas path, particularly when the bleed location is in the bypass duct or the high-pressure compressor. It is also found that the utilization of a fuel–oil heat exchanger improves the specific fuel consumption at a higher rate than an air–oil heat exchanger. For the performance characteristics of the examined engine, the specific fuel consumption benefit with the former is 1.33%, while for the latter it is 0.38%.