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 w as experimentally investigated using CO2-enhanced Filtered Rayleigh Scatter ing. The 4: 1 elliptic cone was tested at Reynolds numbers ranging from 0.4 4 x 10(6) to 3.5 x 106, based on free stream conditions and streamwise dist ance 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 stage s of transition reveal for the first time that transition begins with the e mergence of small-scale structures near the centerline axis of the cone (mi nor axis), rather than in the outboard cross-flow region. The three-dimensi onal character of these structures is further explored by simultaneously im aging the planform and spanwise planes. (C) 2000 Editions scientifiques et medicales Elsevier SAS.