Glow Discharge Visualization of Hypersonic Separated Flow past Cylinder/Plate Juncture

In this study, we will try to apply a glow discharge technique to examine the vortical structure around a circular cylinder placed perpendicular to a flat plate in a hypersonic flow. Our purpose is twofold: to demonstrate the capability of the glow technique and to extend our understanding of the flowfield up to hypersonic regime. The experiment is conducted in a gun tunnel. The test condition is a nominal Mach number of 10 with a Reynolds number of 6 ˆ 10 based on the cylinder diameter. The state of the incoming boundary layer at separation is laminar. A comparison of the glow result with a threedimensional Navier-Stokes simulation shows that the density distribution of the flowfield is highly associated with the spatial distribution of glow spectrum, from which we deduce some main flow features. We emphasize that a multiple-horse-shoe-vortex system, which is essentially similar to that in supersonic regime, is formed underneath the separated shear layer. In addition, oil flow and encapsuled thermochromic liquid crystal visualizations augment this observation.