CENTRELINE – ConcEpt validatioN sTudy foR fusElage wake-filLIng propulsioN intEgration

The positive effect of “wake-filling” on propulsive power requirements has long been known from the field of marine propulsion. Ship propellers are typically located at the aft-body of the vessel and operated within the boundary layer flow close to the ship’s body surface. The physical principle ultilised in this configuration is known as Boundary Layer Ingestion (BLI) or wake-filling propulsion integration. It is also applicable to airborne systems. For large commercial aircraft, the share of viscous and form drag typically ranges between 60–70% of the total drag in cruise. Approximately half of this share can be attributed to the fuselage body, making it the most interesting airframe component to be utilised for the purpose of wake-filling propulsion integration. In a fuselage wake-filling propulsion arrangement, the airflow around the fuselage is ingested by fans or propellers located at the aft-fuselage and accelerated just so that the aerodynamic drag of the fuselage is compensated. Compared to a locally separated compensation of the fuselage drag through jet excess momentum produced by classically installed (podded) engines, wake-filling immediately allows to reduce jet excess velocities, hence, the kinetic energy losses in the aircraft wake. This provides a strong lever for reductions in aircraft fuel consumption. CENTRELINE works on a particularly promising overall configuration for fuselage wake-filling propulsion integration. The basis of this is a single boundary layer ingesting fan, the so-called fuselage fan, that encircles the aft-section of the fuselage.
In such a configuration fuselage wake-filling is realised in the most straightforward way while offering the full fuselage wake-filling potential (360° installation). A key factor to a successful implementation of such a remotely located propulsive device is a high-efficiency, low-weight system for the power transmission from the centralised power source on board the aircraft. In CENTRELINE, fuselage fan operation is secured through a turbo-electric power train. In comparison to a realistically integrated mechanical drive train concept (cf. EU-FP7 DisPURSAL project), this greatly simplifies the aero-structural integration of the aft-fuselage propulsor.The power supply in the electrical transmission is realised by generator off-takes from advanced geared turbofan engines, featuring specialised design optimisation. The overall systems configuration pushes the boundaries for light-weight electric machinery, ultra-efficiency turbo engine design and aero-structural systems integration. Combining such novel propulsion system technology with the well-proven tube-and-wing aircraft layout makes a great potential for aircraft product innovation in the future. The innovative capacity is even strengthened by the CENTRELINE technology concept being widely complementary to other technologies that address the thermal or the propulsive efficiency of power plant systems as well as advanced wing aerodynamic and light weight aero-structural technologies.