Laminar-turbulent transition in a Mach 8 elliptic cone flow

To examine the influence of crossflow on transition in a hypersonic boundary 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 visualization 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 relatively complex, with highly skewed velocity profiles and a pair of symmetric vortices on the top centerline of the cone. Transition in the elliptic cone flow was found to be significantly different than transition in hypersonic flow over planar and axisymmetric configurations, which is driven by the second mode instability. In the elliptic cone flow the transition front was nonuniform, with early transition near the top centerline and delayed transition near the leading edge. Rope waves were observed on both tbe leading edge and top centerline; unusual elongated streaks were observed on the top centerline Transition on the top centerline may be related to an instability of the inflectional boundary-layer velocity profiles in that region. A traveling crossflow instability is probably important in the vicinity of the shoulder of the cone, and tentative evidence of a stationary crossflow instability was obtained with the introduction of artificial roughness.