Boundary layer ingestion (BLI), in which part of an aircraft airframe's boundary layer is ingested by the propulsors, has the potential to provide significant improvements in fuel efficiency compared to conventional engine installations. The wind tunnel tests of the D8 "double-bubble" aircraft in back-to-back BLI and non-BLI configurations constitute a proof-of-concept for the use of BLI in transport aircraft. These were carried out as part of a NASA N+3 project led by MIT in collaboration with Aurora Flight Sciences and Pratt & Whitney.
This presentation will cover the wind tunnel experiments, with emphasis on the quantification of the power-saving benefit of BLI. It will introduce the power balance method for analyzing highly-integrated aircraft configurations, and how it was applied to the D8 tests to determine the aerodynamic benefit of BLI. The different sources of benefits with BLI will be related to the dissipation sources in the flowfield, and an analysis framework for aircraft with BLI will be presented.