This paper presents an experimental study on shock-wave/turbulent-boundary-layer interaction unsteadiness and delves specifically into the shear layer’s role. A range of axisymmetric step-induced interactions is investigated and the scale of separation is altered by over an order of magnitude – mass in the recirculation by two orders – while subjected to constant separation-shock strength. The effect of the separated shear layer on interaction unsteadiness is thus isolated and its kinematics are characterised. Results point at a mechanism whereby the depletion of separated flow is dictated by the state of the large eddy structures at their departure from the bubble. Low-frequency pulsations are found to adjust in response and sustain a reconciling view of an entrainment–recharge process, with both an inherent effect of the upstream boundary layer on shear layer inception and an increase in the mass locally acquired by eddies as they develop downstream.

No abstract

Preliminary findings are presented for an ongoing fundamental experimental study of shock-induced separation of transitional hypersonic boundary layers. The basic reference boundary layer state is a laminar flow; use of a single isolated roughness element produces a train of turbulent spots downstream of the element, which then impinge upon the separation region. This paper focuses on the pressure results and presents instantaneous distributions for a single run, corresponding to various states as turbulent spots convect over the separation zone. The spot scale is sufficiently large that the separation bubble locally collapses from the laminar state to a fully attached turbulent flow, before beginning to recover to the laminar state once the spot has passed. The twin objectives of the work are to provide insight into the flow physics and to provide benchmark data suitable for use by the CFD community.

This paper uses measurements of surface heat transfer to study roughness-induced turbulent wedges in a hypersonic boundary layer on a blunt cylinder. A family of wedges was produced by changing the height of an isolated roughness element, providing conditions in the following range: fully effective tripping, for the largest element, with a turbulent wedge forming immediately downstream of the element; a long wake, in length several hundred times the boundary layer thickness, leading ultimately to transition; and retention of laminar flow, for the smallest element. With appropriate element size, a fully intermittent wedge formed, comprising a clear train of turbulent spots.

No abstract