PIV Investigation of the Effects of Shock Generator Wedge Angle and Trailing-Edge Expansion Waves on Impinging Shock/Turbulent Boundary Layer Interactions over a Cylinder

Stereoscopic particle image velocimetry (SPIV) measurements were performed within a supersonic wind tunnel at a freestream Mach number of 3.4 to quantify the interaction of a series of oblique shock waves with a turbulent boundary layer flow on the windward plane of symmetry of a cylindrical body. The first goal was to experimentally investigate the effects of different planar shocks generated using wedge-shaped shock generators with turn angles of θ = 10^◦,15^◦ & 20^◦. For these experiments, the shock generators length extended far downstream enough of the interaction regions, such that the induced shock strengths were unaltered from any wedge trailing-edge effects at the impingement location over the cylinder. The second goal was to carry out similar tests using short shock generators to test the effect of expansion waves extending from the wedge trailing edge onto the body surface. The size of the wedges was chosen to match the configuration used in previous literature. While the large wedges produced a combination of weak and strong interactions, the presence of expansion waves from the small wedges resulted in only weak interactions and appreciable changes to the interactions size and unsteadiness. Results show that the strong separation on the body is a highly unsteady closed bubble structure with intermittent large flow reversal, whereas the weak separation is an open-type region. The measured turbulence statistics reveal that the amplification of Reynolds stresses is substantially higher in the strong versus the weak interactions, both showing maximum magnitudes at quite different locations. The present windward-side observations agree well with the literature, bridging the gap between the published findings on such complex flow field and revealing novel features that both match and differ from that observed in 2-D and 3-D SBLI canonical configurations.