Experimental Studies of Transitional Boundary Layer Shock Wave Interactions

Abstract

Abstract : Transitional shock wave/boundary layer interactions are studied with planar imaging techniques. The interaction is generated by a cylinder mounted on a flat plate in a Mach 5 flow. Planar laser scattering (PLS) and particle image velocimetry (PIV) are used to visualize the flow structure. Images are obtained in streamwise-spanwise planes (plan view). Earlier work focused on investigating similar interactions with tripped boundary layers, whereas the current work focuses on the case where transition occurs naturally. One goal of this preliminary study was to see if repeatable interactions could be generated. Imaging was conducted for three downstream locations of the cylinder. The PLS imaging revealed that the transitional interactions resulting from an untripped boundary layer are similar to those generated by tripping. In general it is observed that the separated flow region of transitional interactions exhibits larger variations in their scale and shape than fully turbulent interactions. When the cylinder is farthest upstream (5.3 diameters from leading edge) two types of separation shock are seen: an apparently laminar shock along the plate centerline and a turbulent one in the outboard region. As the cylinder is moved downstream (10.7 diameters), this dual structure is not as apparent, which is consistent with the upstream boundary layer becoming more turbulent. Finally, at 16 diameters downstream the interaction exhibits extreme variations in its shape, which we believe to be caused by sidewall interference. The PIV measurements largely confirm these qualitative observations.