Laminar-turbulent transition in a Mach 8 elliptic cone flow

To examine the influence of crossflow on transition in a hypersonic boundar y layer, an experimental and computational Study was made of a Mach 8 flow over a sharp-nosed elliptic cone of 2:1 cross section. Extensive how visual ization was carried out experimentally, including schlieren photography and surface oil-flow visualization. Mean pressure and heat flux were measured at the wall of the wind-tunnel model. For comparison with the experiments, a computation of the basic state flow was carried out using the parabolized Navier-Stokes equations. The basic state laminar flow was found to be rela tively complex, with highly skewed velocity profiles and a pair of symmetri c vortices on the top centerline of the cone. Transition in the elliptic co ne flow was found to be significantly different than transition in hyperson ic flow over planar and axisymmetric configurations, which is driven by the second mode instability. In the elliptic cone flow the transition front wa s nonuniform, with early transition near the top centerline and delayed tra nsition near the leading edge. Rope waves were observed on both tbe leading edge and top centerline; unusual elongated streaks were observed on the to p centerline Transition on the top centerline may be related to an instabil ity of the inflectional boundary-layer velocity profiles in that region. A traveling crossflow instability is probably important in the vicinity of th e shoulder of the cone, and tentative evidence of a stationary crossflow in stability was obtained with the introduction of artificial roughness.