# Exchange Rate Analysis for Ultra High Bypass Ratio Geared Turbofan Engines
### Exchange Rates  
The exchange rate analysis was used to describe the effects of deviations in the parameters from the reference condition in the performance and operability of the whole system. As a result, a correlation function was generated based on a systematic approach to find the relationship between engine exchange rates and the signatures from the engine reference database [33]. Therefore, the results of the exchange rate analysis carry high credibility. Thus, it is a powerful tool to analyze the technology summary [34] and to be used in the design procedure for the development of next generation gas turbine engines [35].  
In general, two scenarios were examined, namely the design point (DP), and the synthesis exchange rates. In the former, the engine geometry was changed, and the cycle was fixed. The objective was to study the impact of a small change in leading component performance levels on engine DP performance parameters. In synthesis exchange rates, the engine geometry is fixed (i.e., fixed components defined for the DP) and engine cycle changes. The objective was to study the effect of changing a cycle parameter with the rest of the engine hardware unchanged.  
[PERSON] et al. [36] recently presented a comprehensive study on the utilization of exchange rate analysis for a diagnostics-oriented modelling approach of micro gas turbines for fleet monitoring and maintenance optimization [36]. They used an exchange rate analysis to develop a scheme for fault identification and finally presented the correlation coefficients between exchange rates and signatures for their case studies with a single fault. The exchange rate analysis was also used to explore the effect of turbine stage efficiency on fuel consumption in [37] by utilizing the fundamentals of sensitivity analysis on component efficiencies [38] and Brayton cycle [39] in a zero-dimensional feature. The results of the analysis showed that by increasing the efficiency of the first stage of a turbine from 82% to 84% in an aerial engine, the fuel consumption decreased by 1%.  
On future high bypass ratio engines, in which significant heat load will be generated through the use of a power gearbox, a much higher amount of heat will have to be managed, which will further impose the importance of designing a thermal management system that can both manage excess heat safely and reliably and improve engine specific fuel consumption.  
Consequently, the current work investigated the exchange rates on SFC for different architectures of a thermal management system of a UHBR-GTF engine. More specifically, it assessed the impact of bypass pressure loss and air mass extraction from the bypass flow. The investigation also included the effect of core mass flow extraction and the power offtake from the high pressure turbine (HPT). Both DP and synthesis exchange rates results were presented and discussed. Therefore, the following section provides the problem definition, while Section 3 provides a description of the engine model. The latter also includes the design point definition and the engine performance results for a flight profile. The SFC exchange rate results are discussed in Section 4, followed by the conclusions.