How does boundary layer ingestion affect propulsion system design and integration?

Boundary Layer Ingestion (BLI) captures aircraft fuselage boundary layer in the propulsor inlet, reducing wake energy loss and improving propulsive efficiency by 5-10%. Design implications: Inlet distortion from ingested boundary layer (must maintain compressor operability), Fan design for distortion tolerance (robust blade aerodynamics, structural integrity), Aft-mounted propulsor integration (structural, thermal), and Control system adaptation for varying inlet conditions. Analysis requires coupled CFD of airframe and propulsion system, distortion-tolerant fan design using full-annulus unsteady simulations, and wind tunnel testing with distortion screens. NASA and industry (STARC-ABL, BWB concepts) actively researching BLI for future transports. May enable 10%+ fuel burn reduction.