Characterizing the Streamwise Development of Surface Roughness Effects on a Supersonic Boundary Layer

Two-component particle image velocimetry was employed to measure the effects of the mechanical distortions caused from surface roughness topologies on a Mach 2 boundary layer. The first goal of this study was to characterize the mechanical responses of the supersonic boundary layer to various roughness topologies. These responses were characterized in ensemble averaged mean velocity characteristics as well as turbulent intensity responses through the Reynolds Stresses. The second goal was to characterize the streamwise development of the mechanical distortions over a diamond roughness topology. Measurements were taken at three streamwise measurement locations to measure the streamwise mechanical distortion development. Lastly, near-wall streamwise-elongated coherent structures were characterized utilizing a streamwise-spanwise oriented laser sheet. Instantaneous velocity vector fields and two point autocorrelations were used to characterize the spatial orientation of the near-wall coherent structures. Baseline characteristics of the supersonic boundary layer were determined over a hydraulically smooth floor insert.The mean and turbulent statistics compare well to other results when scaled by the roughness friction velocity. Ensemble averaged outer-scaled streamwise velocity profiles showed a velocity deficit in the near-wall region. Inner-scaled boundary layer profiles showed a downward vertical shift of 3 and 4.5 for the diamond roughness and realistic roughness topologies, respectively. These values show similar mechanical responses to the results seen by Ekoto et al.[3] in a Mach 2.86 boundary layer. The roughness effects were shown to increase in magnitude along the streamwise distance.