# Exchange Rate Analysis for Ultra High Bypass Ratio Geared Turbofan Engines
## 6 Conclusions  
The performance parameters and design characteristics for the next generation of ultra-high bypass ratio geared turbofan engines were presented in this paper. This type of engine is the best candidate to be assumed with a 2025 entry into a service level of technology. By using a systematic categorization, it is concluded that the ultra-high bypass ratio geared turbofan engine has the potential to deal with the remaining challenges for future propulsion systems in air travel applications.  
For this type of engine, thermal management is a big challenge, as the increased BPR requires a larger power gearbox, and this will increase drastically the generated heat loads. The utilization of AOHE and FOHE has an impact on engine performance.  
In order to assess this impact, the design point and synthesis exchange rates analysis were conducted to study the relationship between changes in component performance levels and changes in engine parameters. The exchange rates results show a linear relation between the amount of bypass duct pressure loss and deterioration of the engine SFC. The exchange rates analysis on the air bleed extraction (LPC bleed to the bypass flow, HPC bleed to the bypass flow, bypass bleed overboard, LPC bleed overboard, and HPC bleed overboard) confirms that any air bleed from the bypass duct has a considerable deterioration in SFC (i.e., for 4% HPC air bleed, SFC deteriorates 4.7% and 6.6%, when air is driven to bypass and overboard, respectively).  
It was found that any pressure loss in the bypass duct causes a considerable increase in the SFC. For the engine under investigation with a BPR of 15 and thrust level of 111.2 kN at take-off, a 4% pressure loss in the bypass duct causes a 7% SFC increase at cruise conditions. Therefore, minimizing the pressure loss in the AOHE should be a priority for the designer.  
It was also found that the utilization of FOHE improves the SFC at a higher rate than AOHE. For the performance characteristics of the examined engine, the benefit was 1.33%, while for the AOHE  
Figure 19: SFC exchange rates vs. HPT power offfake.  
it was 0.38%. Therefore, for the thermal management system design, the utilization of FOHE should be done to the maximum level trying to increase the fuel temperature to the maximum permissible level.  
The effect of HPT power efftake was also investigated, and the results confirm that the increase of this work caused a deterioration in SFC (i.e., when the HPT auxiliary work increases by 133%, SFC deteriorates by 0.96%).  
The reported results and design could be utilized for the detailed design, optimization, and development of the next generation of civil turbofan engines for 2025 and beyond.  
Conceptualization, T.N. and P.P.; methodology, T.N. and S.J.; software, S.J.; validation, T.N., S.J., and D.B.; formal analysis, T.N. and P.P.; investigation, T.N., S.J., and D.B.; resources, P.P.; data curation, D.B.; writing--original draft preparation, T.N.; writing--review and editing, T.N., S.J., and D.B.; visualization, T.N.; supervision, T.N. and P.P.; project administration, P.P.; funding acquisition, T.N. and P.P. All authors have read and agreed to the published version of the manuscript.  
This work was conducted under the Ultra High Bypass Ratio Aero Engine Thermal Systems (UHBR Thermals) Programme, funded by Meggitt PLC and Innovate UK (grant No: 91855-263266). The authors declare no conflict of interest.