Investigation of Realistic Material Surface Roughness on a Supersonic Boundary Layer

The effect of surface roughness in supersonic and hypersonic flight has been an area of active research for the last half century. Though knowledge has progressed significantly, the importance and scale of roughness effects on the high-speed flow environment, as well as the flight body, is still an area of active research. As ground testing capabilities continue to improve, as well as diagnostic techniques, new aspect of roughnesses' relation to the high-speed flow environment can be tested.

In support of this effort, the University of Tennessee Space Institute (UTSI), in collaboration with the University of Dayton Research Institute and the Air Force Research Laboratory, sought to better understand the effect of roughness height and geometry on a turbulent boundary layer. Testing was completed in UTSI's M=4 Ludwieg tube on a variety of models capable of hosting varying roughness types. This included a 6^o cone with detachable, 3D-printed cone tips, and a 23" hollow cylinder model, with removable 3-D printed sleeves. 3-D printing of both cone tips and sleeves allowed for variability in roughness geometry and size. Specifically, 3-D printed sleeves were designed to mimic relevant materials being studied for flight vehicles, such as ceramic matrix composite (CMC) weaves. These models were tested with the diagnostics of high-speed schlieren imaging and focused laser differential interferometry (FLDI). Novel image and data processing tools were used to further understand the data collected. All of this study was done for the purpose of further understanding the importance, effect, and inner workings behind surface roughness interactions with a hypersonic flow environment.