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A flexible and extensible modular multi-disciplinary framework has been developed, in order to undertake design space exploration and multi-disciplinary optimization assessments of novel Ultra High Bypass Ratio (UHBR) and open rotor concepts at aircraft mission level. The framework comprises advanced engine performance simulation modelling capabilities, coupled with turbomachinery component aerodynamic design, flow path and weight estimation as well as aircraft performance, for mission level assessments. Advanced numerical solvers and optimization algorithms are integrated in the framework. The capabilities developed are used to optimize the design of a UHBR (Ultra High Bypass Ratio) geared turbofan configuration with a Variable Area Nozzle, for short/medium range applications and an EIS of 2025. The objective is to minimize the amount of fuel burn, an objective that leads to both minimum CO2 production and fuel costs. Both single and multi-objective (several missions) optimizations are performed, for representative civil aircraft missions (range from 300 nm to 4000 nm). Based on the technology level assumptions made and the constraints imposed in the design, fuel burn reduction (and therefore CO2 emissions) in excess of 18% are anticipated, compared to conventional current day engines. The work has been undertaken within Clean Sky 2 project DEMOS, in line with efforts to meet the long term ACARE targets to reduce aircraft CO2, NOx and noise emissions.

In this paper, the main modelling aspects for setting up an Ultra-High Bypass Ratio (UHBR) Geared Turbofan (GTF) engine performance model with Variable Pitch Fan (VPF) and/or bypass Variable Area Nozzle (VAN) are first described. Next, a multi-point design (MPD) structure is presented considering performance requirements and thermal, structural and aerodynamic constraints at top-of-climb, take-off and cruise conditions. Using the MPD approach, multi-parametric studies are then carried out to generate a design space of engine cycles according to the specified targets and limits which are representative of a UHBR GTF in a narrow body aircraft for short range applications with an Entry Into Service (EIS) of 2025.