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.

An experimental facility is currently operating at Cranfield University in the UK and it is being used to explore supercritical carbon dioxide as a working fluid for future bottoming power cycle applications. The initial objective of this experimental programme is to de-risk and demonstrate the robustness of a closed-loop system, whilst proving the function and performance of individual components and various measurement and control modules. This paper describes the first operational experience gained whilst operating the test facility. More specifically, it summarizes the lessons learned from the commissioning phase and first test campaigns carried out in 2018.

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.

Since 2018, there is an experimental supercritical carbon dioxide (sCO2) facility operating at Cranfield University. The purpose of this rig is to enable the exploration of supercritical carbon dioxide as a working fluid for future bottoming power cycle applications and, more recently, for thermal management applications. The core of the rig is a transcritical closed loop, which has recently been upgraded. The upgrades include an increase in the number of measurement stations, changes to the types of measurements taken, as well as the addition of a new, dedicated data acquisition system. A summary of some of the lessons learned from different test campaigns conducted from 2018 to 2021 is provided, along with a discussion on the measurement upgrades performed. The experience obtained with this rig, as recounted in this paper, could be relevant to similar test rigs or future power cycles applications.

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