# Exchange Rate Analysis for Ultra High Bypass Ratio Geared Turbofan Engines
###### Abstract  
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%.  
aero-engine; exchange rates; thermal management Article Exchange Rate Analysis for Ultra High Bypass Ratio Geared Turbofan Engines [PERSON] 1,*  
Phase 1 (1970s) [2; 3; 4; 5; 6]: Pioneering Work. The first studies were undertaken, resulting in some landmark analytic architectural design. In the first years of the 1970s, studies were concentrated on review and survey of gas turbine development progress since it first emerged. However, later studies started predicting the conceptual future trends and proposing structures for future large civil turbofans for air travel.
* Phase 2 (1980s) [7; 8; 9; 10]: Growth. Between 1980 and 1990, there were fundamental studies about different concepts for future aircraft engines. Concepts such as aircraft counter rotation propellers and ultra-high bypass ratio (UHBPR) turbofan engines were considered in this period.
* Phase 3 (1990s) [11; 12; 13; 14; 15]: Detailed design. Comprehensive studies based on detailed design and analysis (which largely focused on modification of the previous concepts) and real applications were published. Rolls Royce plc contributed widely in this phase. The main objectives of research studies in this decade were to:
* Examine the parameters that influence the design of new engines for large transport aircraft
* Optimize the installed SFC
* Consider weight and cost effects
* Identify the technology necessary to achieve a competitive product
* Phase 4 (after 2000) [16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31]: Development and Optimization. From 2000 to the present day, more detailed results were published that largely focused on optimization algorithms and multidisciplinary design procedure and its applications in propulsion system design and performance analysis. The focus of the research studies published in this phase can be divided into two main topics:
* Modification of previous concepts and suggestions for future trends
* Optimization of current concepts for future applications Following the above-mentioned literature and phases, the following summary can be made:
* Geared turbofan engines (GTFs) with ultra-high bypass ratios (UHBRs) would be the best option for the next generation of propulsion systems [18; 20; 21; 24; 25; 31].
* An optimal engineering design procedure is required to design/set the performance parameters for the engine to deal with future limitations and targets set by organizations and industries [26; 27; 28; 29; 30].