Performance analysis of turbo-electric propulsion system with fuselage boundary layer ingestion

Artikel i vetenskaplig tidskrift, 2021

A propulsion system analysis of an aircraft concept featuring a fuselage tail cone integrated turbo-electrically powered fan is presented. The aircraft has two underwing podded geared turbofan engines and an aft-fuselage mounted boundary layer ingesting fan. The fuselage fan is driven by an electric motor that is powered by power offtake from the main power plants under the wing. A long-range tube-and-wing aircraft with a year 2050 entry into service is used as a reference. A coupled multidisciplinary method for system level assessment of the turbo-electric boundary-layer ingesting propulsion system is presented. A correlation-based method is used to predict fuselage drag and a series of optimizations are carried out for a range of fuselage fan diameters. The optimal level of ingested drag is 30%-57% of the total fuselage drag, resulting in a net reduction in mission fuel burn of 0.6%-3.6% depending on technology assumptions. Further analysis reveals that installation effects, mainly increased mass, offset some of the gains of boundary layer ingestion for the smallest fuselage fan sizes. For larger fan sizes, it is instead the losses in the electric machinery together with the lower efficiency of the fuselage fan, compared to the main engine fan, that compensate for the gains from boundary layer ingestion. However, the by far strongest effect for determining the optimal level of ingested drag is that it is very difficult to obtain a net benefit from ingesting the half of the total fuselage drag contained in the outer part of the boundary layer. The benefit is outweighed by losses in the electric transmission system, installation effects and efficiency deficits of having an aft-mounted fan instead of larger size under-wing main engines. This is true also under the assumption of radical technology such as superconducting electric machinery. It is concluded that the studied aircraft architecture, despite having a high theoretical potential, faces a large difficulty in beneficially ingesting the significant amount of the fuselage drag contained in the outer part of the boundary layer. This severely limits its potential to substantially reduce the fuel burn compared to a conventional twin-engine tube-and-wing aircraft in the year 2050 timeframe.