Fin-induced Shock Boundary Layer Interactions on a Flat Plate and Hollow Cylinder at Mach 5

An experimental investigation of Shock Boundary Layer Interaction (SBLI) topologies around unswept fins in Mach 5 flow has been conducted with a range of Reynolds numbers, boundary layer states, and fin-base shapes. Geometries are based on the DLR STORT flight test program, featuring a θ_f = 20^◦ deflection and r_f /h_f = 0.015 leading edge bluntness. The fin is mounted on a cylindrical base geometry with radius r_c/h_f = 1.37. A laminar flat-plate fin-induced SBLI is investigated at Re_xf = 2.8 × 10⁶ in a Mach 5 in-draft wind tunnel, and characterized with oil-flow visualization and mean wall-pressures. Lines of flow separation and reattachment were observed clearly in each technique, respectively. A novel oil-mixture featuring amyl acetate was required to combat issues with the low freestream pressure in the in-draft facility. Turbulent fin-induced SBLIs are investigated on a hollow cylinder at 4.0 × 10⁶ < Re_xf < 16.1 × 10⁶ in a Mach 5 Ludwieg tube. The cylinder was designed to maximize modularity and scaled with the fin to match flight proportions. Linear Stability Theory was applied to various leading edge profiles to inform the model design. Surfaces were coated with a thin vinyl film to facilitate topological characterization using Infrared (IR) thermography. While qualitatively similar to the laminar results, the SBLI structure beneath the fin leading edge appeared noticeably tighter, with bifurcation of the separation lines further outboard suggesting secondary separations. Away from the fin, separation lines skew downstream due to the relief effect of the base curvature. A subtle Reynolds number dependence was observed with the separated region growing at higher Re_xf . The current investigation is ongoing, with future work planned to bridge observations between these configurations.