A Tail-Integrated Boundary-Layer Ingesting Propulsion System for Turbo-Electric Aircraft

Abstract

In this thesis, we present conceptual design guidelines and results for a tail-integrated propulsion system for turbo-electric aircraft with boundary layer ingestion (BLI). This includes (i) definition of tail BLI electric fans and (ii) integration of the BLI propulsors on an aircraft tail, to meet the propulsive power requirements and performance goals, i.e. separation-free and shock-free operation with fuel burn reduction, compared with a baseline aircraft for the same mission. The assessment of BLI benefits incorporates CFD and TASOPT analyses, with emphasis placed on utilizing these analyses not only to identify potential challenges for integration of the BLI propulsors, but also to characterize the underlying mechanisms and thus establish the physical rationale for resolving these challenges.

The conceptual design resulting from the guidelines has nine BLI propulsors with electric fans on an axisymmetric tail, which is installed on a baseline single-aisle aircraft with twin underwing turbofans without BLI. For the tail-integrated BLI electric fans, the guidelines include the required fan loss buckets, and non-axisymmetric sta tors, to mitigate the fan efficiency drop due to rotor inlet incidence distortion. The design of the tail-integrated propulsor illustrates the aerodynamics of the propulsor inlet, nacelle, and nozzle that enable separation-free and shock-free operation at the cruise condition. The benefit of the defined tail BLI and twin underwing turbofan aircraft configuration is 10.4% in Propulsion Fuel Energy Intensity (PFEI) at a cruise Mach number of 0.8 and an altitude of 35100 ft, compared to a baseline twin underwing turbofan configuration. The sensitivity study shows that a 1% increase in installed (i.e. with BLI) fan efficiency translates to 0.8% rise in the PFEI benefit.