Response of a supersonic turbulent boundary layer to periodic surface roughness
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In the present study, the response of a high-speed (M = 2.86), high Reynolds number (Re 60,000) supersonic turbulent boundary layer to local distortions created by periodic surface roughness (k s+ 80) was examined. Two roughness topologies (square blunt and streamlined diamond elements) were compared. An aerodynamically smooth wall was included in the test matrix for comparison purposes. The measurements included: high resolution planar contours of the mean and fluctuating velocity, pitot pressure profiles, pressure sensitive paint and schlieren photography. The roughness topology was found to have a profound effect on the mean and turbulent flow structure. The square roughness pattern studied here produced the expected variations. However, the diamond shaped roughness elements produced attached oblique shocks on their leading edges with expansions at their trailing edges. This led to localized stabilizing and destabilizing distortions that produced periodic increases and decreases in the turbulence production and thus a periodic mean and turbulent flow structure.