An investigation into parameters affecting separation in normal shock wave/boundary layer interactions (SBLIs) has been conducted. It has been shown that the effective aspect ratio of an experimental facility (defined as δ * /tunnel width) is a critical factor in determining when shock-induced separation will occur. Experiments examining M ∞ = 1.4 and 1.5 normal shock waves in a wind tunnel with a small rectangular cross-section have been performed and show that a link exists between the extent of shock-induced separation on the tunnel centre-line and the size of corner-flow separations. In tests where the corner-flows were modified ahead of the shock (through suction and vortex generators), the extent of separation around the tunnel centre-line was seen to vary significantly. These observations are attributed to the way corner flows modify the three-dimensional shock-structure and the impact this has on the magnitude of the adverse pressure gradient experienced by the tunnel wall boundary layers.

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Wind tunnel experiments were performed to quantify the aerodynamic benefit of boundary layer ingestion (BLI) for the D8 transport aircraft concept. Two powered 1:11 scale, 13.4 ft span models, in BLI and non-BLI versions, were tested at the NASA Langley 14×22 Foot Subsonic Wind Tunnel to directly compare their performance. The models share the same basic airframe and propulsor units for the most direct comparison. They are also fully tripped to make the measured BLI benefit results scalable to the full-size aircraft. The comparison metric is the propulsor power required to produce a given net stream-wise force on the entire aircraft. The results show that the model BLI propulsors require 6% less electrical power at the simulated cruise point. These experiments provide the first back-to-back assessment quantifying the aerodynamic benefits of BLI for a civil aircraft. The BLI benefit quoted is preliminary in nature because it is defined in terms of electrical power, but we are in the process of obtaining a value in terms of flow power and there is indication that the BLI saving will remain essentially the same.

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