Experimental investigation of boundary layer ingestion into diffusing inlets

An experimental investigation was carried out to examine the flow inside diffuser inlets ingesting boundary layers with a thickness of the order of 30–40% of the ducts' throat height, with and without passive flow control consisting of vortex generators (vg's). The first of the three ducts tested was a long semi-circular diffusing duct with no offset. It was examined to study vortical. dynamics in internal flows and the effect of various vg design parameters on their performance and impact on the flow structure inside the diffuser. The other two ducts were shorter than the first duct and both had the same length and diffusion ratio. One duct maintained a semi-circular cross-section throughout its length with no offset, and the second one had an S-shaped offset and changed its cross-section from a semi-circle at the throat to a full circle at the fan face. The flow surveys in the two ducts were compared to understand the effect of offset on flow structure, diffuser performance and vg effectiveness. Duct performance was quantified in terms of pressure recovery and total pressure distortion at the fan face (exit) of the duct. The S-duct also yielded results applicable to aircraft engine inlets as its geometry was similar to that expected on the inlets of the NASA/Boeing Blended-Wind-Body (BWB).