Thrust-Drag and Power Balance Accounting Methods for a Boundary Layer Ingesting Propulsion Configuration

This paper considers the application of two types of performance accounting systems to a boundary layer ingesting (BLI) propulsion configuration to identify features that arise due to propulsion-airframe integration. To do this, a canonical, two-dimensional BLI configuration consisting of a fuselage element propelled by an integrated ducted propulsor has been developed, and aerodynamic forces and power for a range of angle of attack and propulsor mass flow has been calculated using MSES, a viscous-inviscid flow solver for multi-element airfoils. In a traditional thrust-drag accounting, BLI manifests as a negative “interference drag,” equal to 46% of the isolated fuselage element drag at zero angle of attack and design mass flow. The results also show that accounting for changes in vehicle angle of attack before changes in throttle setting reduces variation in the throttle-dependent force and power increments with respect to the angle of attack, suggesting that such an approach may be appropriate for BLI configurations. The second type of accounting system was the Power Balance Method, which has been suggested to be more suitable for the analysis of integrated geometries with BLI. The results show that the boundary layer, wake, and jet dissipation of the BLI configuration vary with configuration angle of attack and mass flow, a behavior that must be considered when using power-based accounting. The analysis also highlights the difficulty in defining separate contributions to viscous dissipation from adjacent surface wake and jet flows that are inherent to BLI configurations.