Flow distortion effects on the aerodynamics and performance of a low-pressure ratio fan in a boundary layer ingestion aft-fuselage propulsor

Turbomachinery operating in boundary layer ingestion propulsion systems can experience substantial performance degradation due to elevated levels of inlet distortion. This paper presents a numerical investigation of the aerodynamics and performance of a low-pressure ratio fan designed for a tail-cone thruster integrated within a hydrogen-electric powertrain. The rotor is assessed in three flight conditions along the climb trajectory using unsteady Reynolds-averaged Navier–Stokes simulations to examine the aerodynamic behavior, the energy exchange mechanisms, and the sensitivity to inflow distortion. The spoiled inflow induces significant excursions of the blade operating point, driven by axial and tangential momentum redistribution at the inlet plane. As a consequence, some azimuthal sectors operate under high blade loading and reduced mass flux, while others exhibit increased mass flow and relative velocity. The continuous migration of the working point toward both stall and choking conditions leads to an overall efficiency penalty of 2.5% in cruise. Earlier in the climb, the less severe distortion progressively attenuates performance degradation, but the operating point excursion is amplified by the reduction in compression characteristic. Under near-stall conditions, the rotor experiences loading levels locally beyond the clean inlet condition, but the blades are able to recover toward higher flow rates without incurring leading edge spillage.