Due to the large disturbance created by the sonic boom, supersonic flight is strictly controlled by the FAA. One way in which to minimize the sonic boom is through shape-tailoring of the aircraft body and of the propulsion system. To this end, a new supersonic engine concept has been proposed, wherein a core turbofan engine, which has a non-axisymmetric external profile due to a protruding gearbox, has been circularized. A new, secondary, bypass with a highly complex internal geometry is created during this process. The high-flow nacelle bypass geometry includes a forward and aft fairing to direct the flow around the gearbox, a set of thin forward guide vanes, and a set of thick, strut-like aft guide vanes. The aft guide vanes, which also serve structural purposes, are used to direct the flow such that the exhaust is a uniform, nearly-full annular cross-section, and to choke and then accelerate the flow to supersonic freestream conditions upon exit. A supersonic wind tunnel facility at the University of Illinois was modified and used to simulate the flow through the aft bypass at approximately 6% scale. In order to aid in understanding the effect of the aft vanes, two models, one with and one without guide vanes, are studied. Due to facility limitations, the design operating condition could not be achieved; a series of off-design operating conditions are tested instead.

Radial pressure surveys are conducted at several azimuthal stations at the inlet to the aft bypass in order to establish in-flow conditions. Static pressure taps on the model surface provide insight into the nature of the flow through the bypass on a per channel basis. An isentropic-case comparison, an estimate of total pressure losses, and mass flow rate calculations were performed. Pressure data were supplemented with schlieren imagery and surface oil flow visualization. Results indicate the flow through the aft bypass is highly three-dimensional and contains a large amount of flow separation in the off-design conditions tested.