Transition studies on an elliptic cone in Mach 8 flow using filtered Rayleigh scattering

Boundary layer transition on a sharp-nosed elliptic cone in a Mach 8 flow was experimentally investigated using CO₂-enhanced Filtered Rayleigh Scattering. The 4:1 elliptic cone was tested at Reynolds numbers ranging from 0.44 × 10⁶ to 3.5 × 10⁶, based on free stream conditions and streamwise distance measured from the cone tip. Boundary layers ranging from fully laminar to late-transitional in character were imaged using single-shot streamwise, spanwise and planform laser orientations. Images taken of the early stages of transition reveal for the first time that transition begins with the emergence of small-scale structures near the centerline axis of the cone (minor axis), rather than in the outboard cross-flow region. The three-dimensional character of these structures is further explored by simultaneously imaging the planform and spanwise planes.