Wall-pressure-array measurements beneath a two/three-dimensional separating/reattaching boundary layer over an axisymmetric backward-facing-step

The surface-pressure signature of the structure within a separated flow region was investigated using a microphone array in the NASA Langley Subsonic Basic Research Tunnel. The experimental set-up consisted of an axisymmetric backward-facing step with a section upstream of the step that could rotate to create a 3D boundary layer at separation. In the flow region, 32 flush-mounted Emkay electret microphones detected the pressure signature and 56 static pressure taps characterized the mean pressure. The taps were also used to align the model in the tunnel. Data were acquired for 2D and 3D flow configurations for Reynolds numbers of 5250 and 10500, based on the step height. A spatio-temporal analysis of the data revealed the dominant flow modes in the separating shear layer and their convective characteristics for both the 2D and 3D cases. Furthermore, similarities and differences between the two situations were investigated.