Boundary layer ingestion benefit of the D8 transport aircraft

This paper presents the experimental assessment of the aerodynamic benefit of boundary layer ingestion for an advanced design civil transport aircraft, the D8 "double bubble," carried out from 2010 to 2015 as part of a NASA N + 3 Phase 2 Program. A back-to-back comparison of non-boundary layer ingesting and boundary layer ingesting versions of the D8 was conducted using 1:11-scale powered models in the NASA Langley 14- by 22-foot subsonic tunnel. The aerodynamic benefit of boundary layer ingestion, as quantified by the difference in mechanical flow power required with boundary layer ingestion relative to the non-boundary layer ingesting case, was measured using two different methods to be 8.6% at the simulated cruise condition when the same propulsors are used on the two configurations. The benefit is found to be insensitive to the various modeling and processing assumptions. A detailed error analysis shows that the benefit has an uncertainty fraction of 0.21 and a 95% confidence interval fraction of 0.035, thus giving high confidence to these results. This work represents the first measurement of boundary layer ingestion performance improvements for a realistic civil aircraft configuration and provides a proof-of-concept for the use of boundary layer ingestion to improve fuel efficiency of subsonic transports.