A separated oblique shock reflection on the floor of a rectangular cross-section wind tunnel has been investigated at M=2.5. The study aims to determine if and how separations occurring in the corners influence the main interaction as observed around the centreline of the floor. By changing the size of the corner separations through localised suction and small corner obstructions it was shown that the shape of the separated region in the centre was altered considerably. The separation length along the floor centreline was also modified by changes to the corner separation. A simple physical model has been proposed to explain the coupling between these separated regions based on the existence of compression or shock waves caused by the displacement effect of corner separation. These corner shocks alter the adverse pressure gradient imposed on the boundary-layer elsewhere which can lead to local reductions or increases of separation length. It is suggested that a typical oblique shock wave/boundary-layer interaction in rectangular channels features several zones depending on the relative position of the corner shocks and the main incident shock wave. Based on these findings the dependence of centre-line separation length on effective wind tunnel width is hypothesised. This requires further verification through experiments or computation. Nomenclature L sep= Separation length (in centre) M = Mach number w = wind tunnel width X = distance from Nozzle end δ = boundary-layer thickness

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A series of experiments have been conducted on a bleed hole array spanning the width of the Cambridge University Engineering Department supersonic wind tunnel at Mach numbers of 1.8 and 2.5. The wind tunnel was run with varying levels of suction, and the flow structure over the bleed array was subsequently mapped with a laser Doppler velocimetry system at a resolution of 0.25 hole diameters or better. The same wind-tunnel setup was simulated using the OVERFLOW Navier-Stokes equation solver. The information obtained was used primarily in qualitative comparisons of flow patterns. Overall good agreement was found in the definition of the expansion fan and barrier shock pattern produced by flow entering the normal holes, as well as three-dimensional flow patterns. Both studies agreed well in terms of measured mass flow rates, to within 1% of the boundary-layer mass flow. The presence of the barrier shock standing off the downstream edge of the bleed holes corresponded with a jet of upward flow, which may provide a mechanism for the generation of streamwise vortices.

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A series of experiments have been conducted on an array of bleed holes spanning the width of the CUED supersonic wind tunnel at Mach numbers of 1.8 and 2.5. The wind tunnel was run with varying levels of suction, and the resulting flow structure over the bleed array was subsequently mapped with a Laser Doppler Velocimetry (LDV) system at a resolution of 0.25 hole diameters or better. The same wind tunnel setup was also simulated using the OVERFLOW Navier-Stokes equation solver. Overall good agreement was found in the definition of the expansion fan and barrier shock pattern produced by flow entering the normal holes, with the production of streamwise vorticity noted in both CFD and experimental studies. The proposed mechanism of vorticity generation is an effect of the barrier shock standing off from the rear edge of each bleed hole, and is predicted by CFD to increase in strength as Mach number increases, as well as when the vorticity is produced by a single hole, rather than an array. Both studies found that vorticity decreases as suction strength is reduced, however the experimental study showed the vortices persist farther downstream than predicted by CFD.