Flowfield of an S-Shaped Inlet with High Boundary-Layer Ingestion Fraction

The efficiency of boundary-layer ingestion (BLI) propulsion systems is closely related to the amount of ingested boundary layer. A high BLI fraction requires low propulsor flow power. In this paper, the internal flow characteristics and performance of an S-shaped inlet with a high BLI, up to 83.8% of the inlet capture height, are explored in detail under a freestream Mach number of 0.75. The results reveal that the middle and lower parts of the aerodynamic interface plane (AIP) section are packed with low-energy flows dominated by a pair of vortices, formed by the coalescence of side and separation vortices. At [Formula: see text], the side vortex, originating near the first inlet bend, is caused by a spanwise pressure gradient, while the side vortex is connected to the horseshoe vortex at the root of the inlet lip at [Formula: see text]. The vortex coalescence results in a sudden increase in the strength of the vortex core and a stepwise increase in circulation ([Formula: see text]). The flow vortex intensity in the inlet is divided into three stages from the distribution of [Formula: see text]. In addition, a reduction in [Formula: see text] increases the intensity of secondary flow along the section, particularly the intensity at the flow separation zone. With increasing [Formula: see text], the swirl intensity decreases, whereas the total pressure distortion index DC60 rises, reaching 0.54, which is beyond the requirement of turbomachinery component flow uniformity.