Experimental Measurements of Hypersonic Instabilities over Ogive-Cylinders at Mach 6

Abstract

Hypersonic boundary layer instability and transition experiments were performed in the low-enthalpy AFRL Mach-6 Ludwieg Tube. The test article was a one-meter long ogive-cylinder model with interchangeable nose tip geometries of varying ogive radius and nose bluntness. Measurements of boundary layer structures instabilities over the body of the model were captured via focused laser differential interferometry (FLDI), two types of surface mounted pressure sensors, and high speed schlieren imagery at nominal unit Reynolds numbers ranging from 3.9*10^6 m^(-1) to 13.6*10^6 m^(-1). Unique boundary layer structures and instabilities were observed that show signs of possible nonlinear interactions leading to breakdown to turbulence. Three primary instability structures were observed that were dependent on ogive radius and nose bluntness. Each instability structure has unique frequency characteristics that are closely tied to the leading edge geometry of the model. The addition of nose bluntness is shown to have an overall delay in transition onset and a possible blunt nose transition reversal is observed as bluntness is further increased. It is also shown that the effects of the ogive radius in addition to nose bluntness alters the flow instability and transition behaviors and is likely tied to a modification of the entropy layer structure. A novel curvature based Reynolds number is proposed to capture the effects of the presence of multiple radii of curvature on the tip geometry and shows signs of collapsing the transition trends of this study to a single curve.