Impact of Boundary Layer Ingestion on the Performance of Propeller Systems for Hybrid Electric Aircraft

Abstract Boundary layer ingestion (BLI) has demonstrated potential for reduced thrust requirements, fuel consumption and environmental impact. An integrated approach is developed for evaluating the performance of propeller systems including BLI propulsors. A rotor model based on lifting-line theory is coupled with a high-order panel method and an integral boundary layer formulation. The impact of BLI on single propeller performance maps is quantified, with efficiencies up to 15% higher compared to uniform freestream conditions. A design space exploration framework is developed for the analysis of BLI effects at propeller system level, including the impact of weight differentiation, installation technology factors, thrust split between rotors and electrical transmission losses. A reference 19-passenger aircraft featuring two wing-mounter propellers is compared with a series of conceptual designs featuring an aft-fuselage BLI propeller and two wing-mounted propellers. A system-wide power saving coefficient is derived for the quantification of performance deltas between the conceptual and the reference system, including all propulsors. For systems with BLI aerodynamic benefits entirely negated by weight penalties, and electrical transmission losses of 10%, power savings of 1.5% are accrued. In a technologically advanced system with 2% reduced thrust requirements due to BLI and 3% transmission losses, power savings rise to 6.5%. This work reveals the anticipated performance potential and limitations of BLI propeller systems for the electrified future fleet.