Aerodynamics of Boundary Layer Ingesting Fuselage Fans
Boundary Layer Ingestion (BLI) potentially offers a large reduction in fuel burn and pollutant emissions. The Propulsive Fuselage Concept features an electrically driven fan at the aft section of the airframe that ingests 360◦ of the fuselage boundary layer. As a result, the distortion at the fan face during cruise is reduced to radial. This paper aims to devise and test a fan design philosophy that is tuned to this inflow distortion. Initially a free-vortex fan design is presented, which is matched to clean, undistorted inflow. The effects of fuselage BLI on the aerodynamics of this fan are investigated. A series of design steps are then presented to develop the free-vortex fan into a new design that is matched to fuselage BLI conditions. Both fan designs have been manufactured and tested within a low speed rig that can make high-resolution flow field measurements. The measured aerodynamics of both fans operating with BLI-type distortion are compared with computational results. The impact of the fan design changes on the aerodynamics and the performance with BLI are evaluated using the test results. This paper 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 test results demonstrate that such a fan can be designed for fuselage BLI that gives increased work input and pressure rise relative to a fan designed for clean flow. The new fan design presented has reduced loading near the hub to account for the incoming distortion, increased mid span loading and negative incidence towards the tip for tolerance to circumferential distortion off- design.