Intercooled turbofan cycles allow higher overall pressure ratios to be reached, which gives rise to improved thermal efficiency. In addition, intercooling allows for the size, weight and exhaust jet velocity of the core to be reduced. For an optimum jet velocity ratio and fixed thrust, the fan pressure ratio and specific thrust are also reduced, which benefits propulsive efficiency. A new intercooled core concept is proposed in this paper, which promises to alleviate limitations identified in previous intercooled turbofan designs. This concept facilitates the installation of the intercooler and reduces core losses at high overall pressure ratios. This engine concept takes advantage of intercooling and the arrangement of the high pressure spool to reach and exceed overall pressure ratios of 80. In addition, given the reduction in core size, bypass ratios beyond 14 have been considered. In order to identify efficiency gains and performance characteristics which are due to the novel arrangement alone, the geared intercooled reversed flow core engine has been compared with a geared intercooled engine with a more conventional core. Finally an optimisation exercise has been carried out to identify the best configuration for both the geared intercooled reversed flow core concept and the conventional core concept. In this paper, it is demonstrated that the geared intercooled reversed flow core concept allows for a 2.3% reduction in block fuel burn. The reductions are due to the improved core efficiency, higher overall pressure ratio as well as efficiency gains from the use of a mixed exhaust. The sensitivity analysis shows that the improvements are highly dependent on pressure losses in the core and bypass stream and that careful design of the mixer chutes and intercooler headers to achieve low losses is essential if the concept gains are to be realised.

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Intercooled turbofan cycles allow higher overall pressure ratios to be reached which gives rise to improved thermal efficiency. Intercooling also allows core mass flow rate to be reduced which facilitates higher bypass ratios. A new intercooled core concept is proposed in this paper which promises to alleviate limitations identified with previous intercooled turbofan designs. Specifically, these limitations are related to core losses at high overall pressure ratios as well as difficulties with the installation of the intercooler. The main features of the geared intercooled reversed flow core engine are described. These include an intercooled core, a rear-mounted high-pressure spool fitted rearwards of the low-pressure spool as opposed to concentrically as well as a mixed exhaust. In these studies, the geared intercooled reversed flow core engine has been compared with a geared intercooled straight flow core engine with a more conventional core layout. This paper compares the mechanical design of the high-pressure spools and shows how different high-pressure compressor and high-pressure turbine blade heights can affect over-tip leakage losses. In the reversed configuration, the reduction in high-pressure spool mean diameter allows for taller high-pressure compressor and turbine blades to be adopted which reduces over-tip leakage losses. The implication of intercooler sizing and configuration, including the impact of different matrix dimensions, is assessed for the reversed configuration. It was found that a 1-pass intercooler would be more compact although a 2-pass would be less challenging to manufacture. The mixer performance of the reversed configuration was evaluated at different levels of mixing effectiveness. This paper shows that the optimum ratio of total pressure in the mixing plane for the reversed flow core configuration is about 1.02 for a mixing effectiveness of 80%. Lower mixing effectiveness would result in a higher optimum ratio of total pressure in the mixing plane and fan pressure ratio.

Significant progress has been made towards the improvement of engine efficiency through the increase in overall pressure ratio (OPR) and reduction in specific thrust (SFN). The implications of engine design extend beyond thermodynamics and should include the consideration of multi-disciplinary aspects related to operation, emissions, lifing and cost. This paper explores the relationship between fuel burn and engine life across the design space of a typical aircraft engine integrated system. In this context the Cranfield University Techno-economic Environmental Risk Analysis (TERA) methodology allows for the assessment of environmental and economic risk when the design of an engine system is at its conceptual stage. It is essentially a multi-disciplinary optimization framework which can be used for design space exploration. Such an approach is necessary in order to assess the trade-off between asset life and powerplant efficiency at the preliminary stage of the design process. A parametric study was conducted in order to assess the sensitivity of major design parameters on engine life and specific fuel consumption (SFC) for a given engine type. The principal failure modes of creep, fatigue and oxidation, were considered for engine life estimation. In addition an optimization study was carried out in order to investigate the trade-off between fuel burn and engine life as Time Between Overhaul (TBO). This was accomplished by integrating aircraft performance, engine performance and lifing models in the TERA Framework. An increase in turbine entry temperature (TET) is required to maintain efficiency at OPR. However, as TET has a strong influence on engine life there is an important trade-off to be made against engine efficiency. The parametric study outlined in this work explores the design space both with respect to engine life as well as efficiency. The optimization study showed that a penalty of 1.42kg additional fuel is required per additional hour of TBO. The fuel penalty is a consequence of sub-optimal design parameters with respect to engine efficiency and is applicable for the presented engine aircraft combination.