Momentum- and Energy-Based Analyses of the Aerodynamic Effects of Boundary Layer Ingestion and Propulsion–Airframe Integration on a Blended Wing Body–Turbofan Configuration

Boundary layer ingestion (BLI) propulsion offers notable benefits for blended wing body (BWB) aircraft, and understanding the interrelated effects of BLI and propulsion–airframe integration (PAI) is critical for early-stage design decisions. This study numerically applies combined momentum- and energy-based analyses to a closely coupled but non-integrated BWB–turbofan configuration enabling a continuous transition from non-BLI to BLI conditions. By introducing an idealized capture streamtube–airframe interaction force, the drag of BLI layout is decomposed into additional and external components, enabling quantification of a lift-to-drag ratio improvement of 1.7–2.6, corresponding to a 7.14–8.27% gain in power saving coefficient (PSC). Additional drag reduction, the primary contributor to total drag savings, is analytically attributed to inlet total pressure loss. The resulting decrease in required thrust under BLI shows strong mathematical correlation with jet dissipation reduction, revealing an intrinsic link between drag reduction and power saving. PAI exerts a significant influence on the BLI benefits, including nacelle cowl drag penalties, significant variations in shock wave location and strength, and notable suppression of both boundary layer and wake dissipation for the portion of cowl immersed in the airframe wake. These findings inform the transition from podded to BLI engine layouts.