Roughness-Induced Transition of Hypervelocity Boundary Layers

Abstract

Experiments were performed in the T4 free-piston reflected shock tunnel to explore the transition process of hypervelocity boundary layers. The experiments took place on a 1000-m-long by 300-m-wide flat plate with a sharp leading edge at representative conditions pertaining to those of an unpublished test of a Mach 12 scramjet. A streamwise row of thin-film heat transfer gauges along the centerline of the plate was used to determine the state of the boundary layer. It was found that, without any boundary-layer trips, the boundary layer remained laminar for the entire length of the plate. Multiple combinations of trip geometry and size were then used in an attempt to force the boundary layer into turbulence. The most successful geometry was the diamond trip configuration, although transition did not occur directly behind the trip. Transition occurred after a period of relaminarization, with the length of the delay region agreeing well with the literature.