Method for Visualizing Viscous Interaction in Hypersonic Low-Density Flows Using Electrical Discharge

The purpose of this study was to determine whether an electrical discharge method can be used to investigate separated flows around models tested in low-density, short-duration hypersonic facilities. To demonstrate the applicability of the proposed method, the visualization of the vortical structure around a circular cylinder placed perpendicular to a flat plate was attempted at a small Knudsen number, where methods commonly used for locating flow separations are ineffective. The density distribution of the flowfield was shown to be associated with the spatial distribution of the glow spectrum. The foci of the horseshoe vortices where the gas density was low enough appeared as dark regions in the visualization, especially in the viscous regime, allowing them to be easily located. In addition, this paper presents a simple conceptual model developed to describe the mechanism behind the present method.