An Experimental Investigation of the Effect of Narrowband Freestream Noise on Fundamental Transitional Shockwave-Boundary Layer Interaction Mechanisms

Recent work at the University of Tennessee Space Institute has demonstrated that the resonant behavior observed in the spectra of cylinder- and blunt-fin-generated XSBLIs is connected to fundamental fluid mechanisms within the boundary layer. Therefore, a test campaign was conducted to characterize the fundamental mechanisms that drive the low-frequency unsteadiness in cylinder- and blunt-fin-generated shockwave-boundary layer interactions, specifically shockwave-boundary layer interactions in which the incoming boundary layer is undergoing a laminar-to-turbulent transition. This research aims to develop a deeper understanding of such interactions and characterize the resonant behavior observed in past work by varying the sweepback angle of a hemicylindrical blunt fin in the UTSI Mach 2 Blowdown Facility.

A z-type schlieren setup provided a qualitative understanding of the flowfield. Quantitative results were extracted from the qualitative images using image processing techniques developed within MATLAB. Previously reported freestream narrowband noise in the University of Tennessee Space Institute Mach 2 Blowdown Facility was measured in the spectral content of the leading-edge shockwave and in the boundary layer. The unswept case showed excellent agreement with previously reported results. However, the swept blunt-fins did not exhibit the same narrowband spectral content as the unswept blunt-fin, but instead showed a broadening of the spectral content as the sweep angle was increased. Additionally, the scale of the interactions decreased, as expected, with the reduction in shock strength. Furthermore, the calculated Strouhal numbers for the swept fins showed excellent agreement with prior research.