The inlet aerodynamic performance of distortion under crosswind for a high bypass ratio turbofan engine was numerically simulated to meet the need of civil aircraft engine/airframe integration. The flow characteristics and their underlying flow physics were investigated. The investigation suggests that: typical flow phenomena of separations

reattachments and ground vortex are found to be the root causes for the inlet distortion under crosswind; there is a sudden intensification in the distortion index as the onset of the inlet internal flow is separated with the increasing speed of crosswind; the civil aircraft inlet tolerance of crosswind would be reduced as the nacelles are affected by the ground vortex phenomenon; the distortion characteristics of civil aircraft inlet are also affected by the engine massflow

whilst the hysteresis loop of the distortion index is captured for the flow separation and reattachments are not exactly repeatable as the engine corrected mass flow rates vary.