Study of a Supercritical Roughness Element in a Hypersonic Laminar Boundary Layer

In this study, the mean flow organization ahead and behind a supercritical cylindrical roughness element immersed in an incoming laminar boundary layer at edge Mach number 6.48 is investigated by means of schlieren visualization, infrared thermography, and planar particle image velocimetry. The schlieren images provide a general overview of the shock-wave system developing around the roughness element. The surface heat transfer map obtained with infrared thermography provides an overall description of the near-wall flow organization in the streamwise and spanwise directions. The off-surface flow topology is inspected with particle image velocimetry in the symmetry plane of the recirculation region upstream of the roughness element. The flow approaching the roughness element separates, forming a main recirculation region adjacent to the stagnation line at the cylinder leading edge. The reattachment vortex is responsible for a heat flux local peak in front of the protuberance. Secondary, more complex local foci and stagnation points are observed upstream of the roughness element, which also correspond to the local maximum of turbulent kinetic energy and surface heat transfer.