Optical Measurements of Viscous Interactions on a Hollow-Cylinder / Flare in a Mach 4 Freestream

Despite decades of research, shock-wave/boundary-layer interactions and laminar-turbulent transition remain uncertainties in the design of hypersonic vehicles. Due to the significant demand for hypersonic capabilities and the relevance of these flow physics to air-breathing, high-lift, hypersonic vehicles, continued study is necessary. In order to support such study at the University of Tennessee Space Institute, two optical diagnostics were investigated for use in the Mach 4 Ludwig tube at the Tennessee Aerothermal Laboratory, focused laser differential interferometry and schlieren. Significant attention was given to the theory behind and application of focused laser differential interferometry to support future work at the University of Tennessee Space Institute. These diagnostics were constructed and utilized in two studies, one investigating a laminar shock-wave/boundary-layer interaction on an axisymmetric hollow cylinder flare geometry, and one tracking the boundary layer transition along a hollow cylinder. Results of these studies show that FLDI and schlieren are an effective method for the non-intrusive study of boundary layer structure and breakdown, and show promising use for the study of shock-wave/boundary-layer interactions. Reported results include spectral distributions from the boundary layer, separation region, and reattachment region of a laminar shock-wave/boundary-layer interaction and from laminar, transitional, and fully turbulent regions in a boundary layer. In this study, the boundary layer was found to transition at a local Reynolds number of Re = 1.71 × 10^5 and gave way to fully turbulent behavior at Re = 3.34 × 10^5.