Micro-ramp flow control of normal shock/boundary layer interactions

Boundary layer bleed has conventionally been used to control separation due to shock wave / boundary layer interactions (SBLIs) within supersonic engine inlets. However, bleed systems result in a loss of captured mass flow, incurring higher drag and ultimately lower propulsion system efficiency. Micro-ramp sub-boundary layer vortex generators (SBVGs) arranged in a spanwise array have been proposed in the past as a form of flow control methodology for shock wave/boundary layer interactions. Experiments have been conducted at Mach 1.4 to characterize flow details of such devices and obtain quantitative measurements of their ability to control the interaction of a normal shock and a turbulent boundary layer. The flow field was analyzed using Schlieren photography, surface oil flow visualization, and particle image velocimetry. An array of three micro-ramps, whose height was scaled to 40% of the incoming boundary layer thickness, was placed ahead of the shock interaction. It was demonstrated that the micro-ramps did entrain higher momentum fluid into the boundary layer which could improve boundary layer health. Specifically, the incompressible displacement thickness, momentum thickness and shape factor were decreased, and the skin friction coefficient was increased, for the SBLI with the micro-ramp array relative to the no-array case.