Investigating Unsteady Dynamics of Cylinder-Induced Shock-Wave/Transitional Boundary-Layer Interactions

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Investigating Unsteady Dynamics of Cylinder-Induced Shock-Wave/Transitional Boundary-Layer Interactions

Combs, Christopher S. / Lash, E. Lara / Kreth, Phillip A. / Schmisseur, John D.

Shock-wave/boundary-layer interactions in laminar and fully turbulent boundary layers have been widely investigated in previous efforts, but relatively little research has been conducted to explore the interactions between a shock wave and a transitional boundary layer. Here, a cylinder-induced shock-wave/transitional boundary-layer interaction is investigated using high-speed Schlieren imaging collected at 100 kHz. The cylinder-induced shock-wave/transitional boundary-layer interaction occurred on a flat plate model in a Mach 1.78 flow upstream of a 3.2-mm-diam cylinder model, which was positioned at 15 unique locations between 6–25 cylinder diameters ( $d$ ) downstream of the flat plate leading edge. Using the Schlieren images, the positions of the upstream influence shock, forward lambda shock, and trailing lambda shock were tracked in a time-resolved manner, permitting a detailed analysis of cylinder-induced shock-wave/transitional boundary-layer interaction dynamics. A spectral analysis of the Schlieren images showed energy peaks in the separated flow region over a band between 2–6 kHz for the transitional interactions, with peaks coinciding with the location of the lambda shocks for the turbulent interactions. This analysis, coupled with the calculation of disturbance convection velocities for the cylinder-induced shock-wave/transitional boundary-layer interaction cases, suggests that the unsteadiness in the interactions investigated in the present study was driven by the instability in the separated flow region.