Aerodynamics of Boundary Layer Ingesting Fuselage Fans

Boundary layer ingestion (BLI) potentially offers significant reductions in fuel burn and pollutant emissions. The propulsive fuselage concept features a fan at the back of the airframe that ingests the 360 deg fuselage boundary layer. Consequently, the distortion at the fan face during cruise is close to radial. This article aims to devise and test a fan design philosophy that is tuned to this inflow distortion. Initially, a free-vortex fan design matched to clean inflow is presented. The effects of BLI on the aerodynamics of this fan are investigated. A series of design steps are then presented to develop the baseline fan into a new design matched to fuselage BLI inflow. Both fan designs have been tested within a low-speed rig. The impact of the fan design changes on the aerodynamics and the performance with BLI are evaluated using the test results. This article presents the successful application of a unique experimental facility for the analysis of BLI fuselage fans. It shows that it is possible to design a fan that accepts the radial distortion caused by fuselage BLI with a modified profile of work input. The new fan design was found to increase the work input by 4.9% and to improve the efficiency by 2.75% relative to a fan designed for clean flow. This new fan design has reduced loading near the hub to account for the incoming distortion and increased mid span loading and negative incidence toward the tip for tolerance to circumferential distortion off-design.