1. V∞ V∞ VExhaust VWake V∞ V∞ VWake + VExhaust Engine
Boundary layer develops
Aircraft
VWake V∞ V∞
Boundary layer develops
Engine
Aircraft
VWake + VExhaust

2. V∞ V∞ V∞ V∞ Aircraft wake (drag) Turbofan exhaust (thrust)
BLI propulsor
Turbofan exhaust (thrust)
The turbofan has to generate enough thrust to overcome the aircraft’s drag (top). A boundary-layer ingesting propulsor could accelerate the slower moving air in the aircraft wake (bottom). The turbofans could then be downsized, since they have to generate less thrust, which leads to weight savings and drag reductions, increasing the overall efficiency.