# Exchange Rate Analysis for Ultra High Bypass Ratio Geared Turbofan Engines
## 3 Engine Model  
With respect to literature survey results, a typical geared 2-spool turbofan engine configuration was set up. The engine architecture was inspired by the CFM56 engine (Figure 3). With the addition of a power gearbox connected to the fan, the cycle parameters were adjusted for the required DP FN assuming a level of technology as entry into service for the year 2025. The schematic of the engine model is shown in Figure 11. The model consists of a fan (core and bypass section), low pressure compressor (LPC), and high pressure compressor (HPC) connected with the HPT (high pressure components) and low pressure turbine (LPT) (low pressure components) and a convergent fixed area nozzle. The model includes different air bleeds from the core gas path to model the secondary flow for compressor surge protection, turbine cooling, and overboard bleed for the aircraft. The first objective was to establish the DP performance of the engine, which was the take-off (T/O) condition. The rationale for this selection was the thrust requirement for the take-off phase and the  
Figure 3: CFM56 drawing [33]. availability of engine data in the public domain. The objective was to achieve the required DP FN at the T/O condition, while at cruise conditions, the engine should satisfy the cruise FN requirement with the maximum compressor and turbine efficiency and within certain safety limits of combustor outlet temperature (COT), fan pressure ratio (FPR), etc. Engine performance was evaluated using Turbomatch, an in-house code developed at Cranfield University and used extensively for research projects. Turbomatch is a 0-D performance simulation code, featuring Off-Design (OD) and transient simulation as well. Turbomatch comprises several pre-programmed modules, known as \"bricks\", which correspond to models of individual gas turbine components. They can be called up to simulate the action of the different components of the engine, resulting finally in output of engine thrust or power, specific fuel consumption, etc. Its modularity, which is supported by the implementation of generic component maps, enables the detailed design of any gas turbine configuration [40; 41]. Scaled generic component maps were used for the engine simulation. Due to the lack of available data related to engine component design, a performance optimization using the Turbomatch code was conducted to evaluate the engine's optimum parameters. Therefore, a number of parameters were varied in specific range (Table 1), and the target was to achieve the following objectives at cruise conditions: \begin{tabular}{l l} \(\bullet\) & max components efficiency \\ \(\bullet\) & min SFC \\ \(\bullet\) & FN = 22,500 N \\ \end{tabular}   
The following values and ranges were used for the simulation based on the literature, industrial consultations, and benchmarking analysis to start the simulation. Using the above-mentioned architecture, assumptions, and objectives full engine performance results were produced demonstrating the engine's behavior under different flight phases to achieve the optimized results. The optimized design parameters for the engine are presented in Table 2. \begin{table}
\begin{tabular}{r l} \hline \multicolumn{2}{c}{**Parameter**} \\ \hline \multicolumn{2}{c}{OPR cruise: min = 35, max = 55} \\ FPR\_hub cruise: min = 1.1, max = 1.8 and FPR\_outer \textgreater{} FPR\_hub \\ TET cruise: min = 1450 K, max = 1650 K \\ BPR cruise: min = 12, max = 18 \\ Max combustor outlet temperature: 1900 K \\ Max compressor outlet temperature: 1000 K \\ Max surge margin parameter Z for all compressors: 0.975 \\ Polytropic efficiency Eta\_poly fan outer cruise: 93\% \\ Polytropic efficiency Eta\_poly fan inner cruise: 94\% \\ Polytropic efficiency Eta\_poly booster cruise: 91\% \\ Polytropic efficiency Eta\_poly HPC cruise: 89\% \\ Polytropic efficiency Eta\_poly HPT cruise: 90\% \\ Polytropic efficiency Eta\_poly LPT cruise: 91\% \\ FN cruise: 18,500 N \\ FN T/O: 111,200 N \\ \hline \end{tabular}
\end{table} 
Table 1: Engine performance optimization parameters.