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This paper presents a description of the physical principles of aerodynamic power savings from boundary layer ingestion (BLI) propulsion and a quantitative evaluation of the BLI benefit for advanced civil aircraft. Control volume and one-dimensional analyses are used to illustrate two major features of BLI: reduction of jet mixing losses due to decreased jet kinetic energy from reduced velocity of flow entering the propulsor and, to a lesser extent reduction of airframe wake mixing losses. Embedded BLI propulsion systems can also enable nacelles with reduced surface area and associated weight and drag, further decreasing the aircraft propulsive power requirement. The required propulsor flow power is shown to decrease with increases in both the amount of boundary layer ingested and the propulsor mass flow, and there is thus no unique way to compare BLI and non-BLI systems. Using the ideas presented, however, the benefit can be assessed for any given comparison. The analysis is applied to an advanced civil transport aircraft concept with 40% of the fuselage boundary layer ingested, yielding a reduction in required propulsor mechanical power of 9% relative to a non-BLI configuration with the same propulsors, in agreement with CFD calculations and wind tunnel

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This paper describes a new conceptual framework for three-dimensional turbomachinery flow analysis and its use to assess fan stage attributes for mitigating adverse effects of inlet distortion due to boundary layer ingestion (BLI). A nonaxisymmetric throughflow analysis has been developed to define fan flow with inlet distortion. The turbomachinery is modeled using momentum and energy source distributions that are determined as a function of local flow conditions and specified blade camber surface geometry. Comparison with higher-fidelity computational and experimental results shows the analysis captures the principal flow redistribution and distortion transfer effects associated with BLI. Distortion response is assessed for a range of (i) design flow and stagnation enthalpy rise coefficients, (ii) rotor spanwise work profiles, (iii) rotor–stator spacings, and (iv) nonaxisymmetric stator geometries. Of the approaches examined, nonaxisymmetric stator geometry and increased stage flow and stagnation enthalpy rise coefficients provide the greatest reductions in rotor flow nonuniformity, and may offer the most potential for mitigating performance loss due to BLI inlet distortion.