# Exchange Rate Analysis for Ultra High Bypass Ratio Geared Turbofan Engines
## 3 Engine Model
In order to assess engine performance at off-design, a full mission analysis was conducted for a long-range aircraft model inspired by an aircraft similar to the Airbus A-320 aircraft equipped with two UHBR-GTF engines. The aircraft performance simulation for a full flight profile was conducted by using Hermes software, an in-house tool developed at Cranfield University. The tool was used to predict aerodynamic characteristics given the required inputs for an aircraft and was combined with Turbomatch in order to calculate the overall performance as an integrated aircraft/engine system. Therefore, for a complete mission, it simulates the trajectory and produces as outputs various engine performance parameters during the flights schedule (i.e., take-off, climb, cruise, descent, and landing) [42; 43]. The aircraft model was set up using Euro-control Base of Aircraft Data (BADA) for an A320 [44]. Simulation of a complete mission was conducted including different operating points (Table 3). Given the setup of the aircraft-engine model, the FN values were calculated for the different flight phases, and the FN fraction relative to T/O is presented in Figure 4. \begin{table}
\begin{tabular}{c c} \hline
**Parameter** & **Unit** & **Values** \\ \hline Mass flow & Kg/s & 446.9 \\ BPR & 15.05 \\ Fan surge margin & 0.862 \\ Bypass FPR & 1.431 \\ Bypass isentropic efficiency & 0.92471 \\ Core FPR & 1.324 \\ Core isentropic efficiency & 0.93724 \\ LPC PR & 5.221 \\ HPC PR & 7.575 \\ OPR & 52.36 \\ COT & K & 1868 \\ TET & K & 1817.7 \\ Combustor P\({}_{\text{loss}}\) & 4.87\% \\ Combustor efficiency & 0.999 \\ HPT cooling flow from HPC & 10\% \\ LPT isentropic efficiency & 0.93518 \\ HPT isentropic efficiency & 0.91254 \\ HPT auxiliary power & kW & 37.5 \\ LPT auxiliary power & kW & 120.0 \\ FN & kN & 111.2 \\ \hline \end{tabular}
\end{table} 
Table 2: DP (T/O) optimized parameters (International Standard Atmosphere (ISA)) for the UHBR-GTF. \begin{table}
\begin{tabular}{c c c} \hline
**Flight Phase** & **Alt (ft)** & **Flight Mach Number** \\ \hline Take off (T/O) & 0 & 0.222 \\ Begin climb & 1500 & 0.388 \\ Climb & 20,000 & 0.589 \\ Top of climb & 32,808 & 0.78 \\ Cruise & 32,808 & 0.78 \\ End of cruise & 36,417 & 0.792 \\ Begin of descent & 37,000 & 0.78 \\ End of descent & 1500 & 0.388 \\ Approach & 1500 & 0.233 \\ Ground idle, taxi & 0 & 0 \\ \hline \end{tabular}
\end{table} 
Table 3: Flight operating points. The OD performance study was done for three different ambient temperature conditions: ISA, cold, and hot day for every operating point. This means that at sea level, there was a -66 \({}^{\circ}\)C (cold day) and +20 \({}^{\circ}\)C (hot day) T\({}_{\rm ambient}\) ISA deviation. For the different altitudes, a variation to T\({}_{\rm ambient}\) was imposed according to standard atmosphere (Figure 5). The simulation was performed by using a constant thrust value for each operating point (i.e., altitude and flight speed, Table 3), reflecting the fact that the aircraft thrust demand does not change with  
about 56 K. The effects were more pronounced at T/O SLS, where the ambient temperature difference was higher. Therefore, in a cold day (i.e., \(-66\)\({}^{\circ}\)C T\({}_{\text{ambient}}\) ISA deviation) the engine could produce the DP FN (111.2 kN) with a reduced TET by 371 K relative to the DP value. In the hot day, TET should be increase by 109 K relative to the DP value for the same FN (Figure 6). The variation of fuel flow (Wf) and SFC was considerable during the different flight operating points due to the different FN requirements and the operating conditions (Figure 7). Wf decreased at cruise conditions, as the FN requirement was lower. The increase at the end of descent was observed due to the effect of flight Ma (Ma = 0.388) at an altitude of 457 m and the thrust requirement for this phase of flight. Figure 6: TET variation due to ISA ambient temperature variation. Figure 7: SFC and fuel flow at different flight phases.