Current FAA regulations limit the speed of civilian passenger jets to subsonic or transonic speeds due to the effects of the sonic boom produced by aircraft during supersonic flight. An engine nacelle design has been proposed that removes low-quality flow from the engine core and reduces the signature of the sonic boom caused by the external protuberances of a traditional engine housing. This new concept incorporates an outer nacelle surrounding the asymmetric engine surface, which creates a highly-complex, secondary bypass flow. Due to the complexity of the flow within this region of the engine, an experimental study has been conducted on the integration of guide vanes within the subsonic portion of the bypass region as the flow is diverted around a partial annular blockage. A wind tunnel facility at the University of Illinois at Urbana-Champaign accommodates an approximately 1/6th scale model that simulates the three-dimensional flowfield around the engine components. In order to observe the influence of the guide vanes on the overall flow quality, tests were also conducted on a model without forward vanes.

Pressure data were collected upstream and downstream of the guide vanes at several axial locations, with high resolution in both the azimuthal and radial directions. In addition to flow speed, flow direction was also analyzed via a five-hole multi-directional probe and surface flow visualization techniques. Experimental flow analysis in this study was conducted to support computational models and to provide insight into techniques that may further improve the flow characteristics within the bypass flow region. Results from the study indicate upstream flow uniformity due to the presence of the guide vanes as well as highly-complex flow features downstream of the vanes.