Electrification of the propulsion system has opened the door to a new paradigm of propulsion system configurations and novel aircraft designs, which was never envisioned before. Despite lofty promises, the concept must overcome the design and sizing challenges to make it realizable. A suitable modeling framework is desired in order to explore the design space at the conceptual level. A greater investment in enabling technologies, and infrastructural developments, is expected to facilitate its successful application in the market. In this review paper, several scholarly articles were surveyed to get an insight into the current landscape of research endeavors and the formulated derivations related to electric aircraft developments. The barriers and the needed future technological development paths are discussed. The paper also includes detailed assessments of the implications and other needs pertaining to future technology, regulation, certification, and infrastructure developments, in order to make the next generation electric aircraft operation commercially worthy.

Key results from the EU H2020 project CENTRELINE are presented. The research activities undertaken to demonstrate the proof of concept (technology readiness level—TRL 3) for the so-called propulsive fuselage concept (PFC) for fuselage wake-filling propulsion integration are discussed. The technology application case in the wide-body market segment is motivated. The developed performance bookkeeping scheme for fuselage boundary layer ingestion (BLI) propulsion integration is reviewed. The results of the 2D aerodynamic shape optimization for the bare PFC configuration are presented. Key findings from the high-fidelity aero-numerical simulation and aerodynamic validation testing, i.e., the overall aircraft wind tunnel and the BLI fan rig test campaigns, are discussed. The design results for the architectural concept, systems integration and electric machinery pre-design for the fuselage fan turbo-electric power train are summarized. The design and performance implications on the main power plants are analyzed. Conceptual design solutions for the mechanical and aero-structural integration of the BLI propulsive device are introduced. Key heuristics deduced for PFC conceptual aircraft design are presented. Assessments of fuel burn, NOx emissions, and noise are presented for the PFC aircraft and benchmarked against advanced conventional technology for an entry-into-service in 2035. The PFC design mission fuel benefit based on 2D optimized PFC aero-shaping is 4.7%.

Establishing an optimal intercooled aeroengine constitutes a coupled problem where the conceptual design of the intercooler and the engine has to be considered simultaneously. The heat transfer and pressure loss characteristics will depend on the choice of the intercooler architecture. Hence, to be able to optimize the performance of an intercooled aeroengine, the performance characteristics of a given intercooler architecture has to be known in the parameter range anticipated for the aeroengine optimization. Here, the conceptual design of a tubular two-pass cross-flow intercooler architecture intended for a turbofan aeroengine application is presented. The internal flow is simulated applying a porous media model for the intercooler tubes, whereas the connecting ducts are analyzed with three-dimensional simulations allowing the assessment of a number of design solutions. The external flow is treated with two-dimensional simulations investigating the external pressure loss and heat transfer characteristics of the two elliptical tube stacks. The intercooler performance is then generalized by developing a reduced order correlation covering a parameter range anticipated for a turbofan conceptual design optimization. The paper constitutes a first effort to establish an open literature complete set of correlations for the prediction of aeroengine intercooler performance.

Aircraft and engine technology have continuously evolved since their introduction and significant improvement has been made in fuel efficiency, emissions, and noise reduction. One of the major issues that the aviation industry is facing today is pollution around the airports, which has an effect both on human health and on the climate. Although noise emissions do not have a direct impact on climate, variations in departure and arrival procedures influence both CO₂ and non-CO₂ emissions. In addition, design choices made to curb noise might increase CO₂ and vice versa. Thus, multidisciplinary modeling is required for the assessment of these interdependencies for new aircraft and flight procedures. A particular aspect that has received little attention is the quantification of the extent to which early design choices influence the trades of CO₂, NOx, and noise. In this study, a single aisle thrust class turbofan engine is optimized for minimum installed SFC (Specific Fuel Consumption). The installed SFC metric includes the effect of engine nacelle drag and engine weight. Close to optimal cycles are then studied to establish how variation in engine cycle parameters trade with noise certification and LTO (Landing and Take-Off) emissions. It is demonstrated that around the optimum a relatively large variation in cycle parameters is allowed with only a modest effect on the installed SFC metric. This freedom in choosing cycle parameters allows the designer to trade noise and emissions. Around the optimal point of a state-of-the-art single aisle thrust class propulsion system, a 1.7 dB reduction in cumulative noise and a 12% reduction in EINOx could be accomplished with a 0.5% penalty in installed SFC.

Although the benefits of intercooling for aero-engine applications have been realized and discussed in many publications, quantitative details are still relatively limited. In order to strengthen the understanding of aero-engine intercooling, detailed performance data on optimized intercooled (IC) turbofan engines are provided. Analysis is conducted using an exergy breakdown, i.e., quantifying the losses into a common currency by applying a combined use of the first and second law of thermodynamics. Optimal IC geared turbofan engines for a long range mission are established with computational fluid dynamics (CFD) based two-pass cross flow tubular intercooler correlations. By means of a separate variable nozzle, the amount of intercooler coolant air can be optimized to different flight conditions. Exergy analysis is used to assess how irreversibility is varying over the flight mission, allowing for a more clear explanation and interpretation of the benefits. The optimal IC geared turbofan engine provides a 4.5% fuel burn benefit over a non-IC geared reference engine. The optimum is constrained by the last stage compressor blade height. To further explore the potential of intercooling the constraint limiting the axial compressor last stage blade height is relaxed by introducing an axial radial high pressure compressor (HPC). The axial–radial high pressure ratio (PR) configuration allows for an ultrahigh overall PR (OPR). With an optimal top-of-climb (TOC) OPR of 140, the configuration provides a 5.3% fuel burn benefit over the geared reference engine. The irreversibilities of the intercooler are broken down into its components to analyze the difference between the ultrahigh OPR axial–radial configuration and the purely axial configuration. An intercooler conceptual design method is used to predict pressure loss heat transfer and weight for the different OPRs. Exergy analysis combined with results from the intercooler and engine conceptual design are used to support the conclusion that the optimal PR split exponent stays relatively independent of the overall engine PR.

Porous media model computational fluid dynamics (CFD) is a valuable approach allowing an entire heat exchanger system, including the interactions with its associated installation ducts, to be studied at an affordable computational effort. Previous work of this kind has concentrated on developing the heat transfer and pressure loss characteristics of the porous medium model. Experimental validation has mainly been based on the measurements at the far field from the porous media exit. Detailed near field data are rare. In this paper, the fluid dynamics characteristics of a tubular heat exchanger concept developed for aero-engine intercooling by the authors are presented. Based on a rapid prototype manufactured design, the detailed flow field in the intercooler system is recorded by particle image velocimetry (PIV) and pressure measurements. First, the computational capability of the porous media to predict the flow distribution within the tubular heat transfer units was confirmed. Second, the measurements confirm that the flow topology within the associated ducts can be described well by porous media CFD modeling. More importantly, the aerodynamic characteristics of a number of critical intercooler design choices have been confirmed, namely, an attached flow in the high velocity regions of the in-flow, particularly in the critical region close to the intersection and the in-flow guide vane, a well-distributed flow in the two tube stacks, and an attached flow in the cross-over duct.