Visualization of Hypersonic Turbulent Boundary Layers Negotiating Convex Curvature

Abstract

The effects of convex curvature on the outer structure of a high-Reynolds number Mach 4.9 turbulent boundary layer are visualized using condensate scattering and analyzed using twopoint spatial correlations, intermittency, and fractal theory. Consistent with other studies, the large-scale flow structures appear to survive the initial expansion. They appear to increase in size, consistent with the effects of bulk dilatation, and undergo a reorientation, leaning farther away from the wall. The intermittency, however, does not change significantly. There is a decrease in the fractal dimension, indicating that the boundary layer interface becomes more regular. Because fractal scale similarity does not encompass the largest scales, this suggests that the change in fractal dimension is due to the action of the smaller-scales, thereby supporting the notion that the small-scale structures are quenched during the expansion. Thus, the effects of convex curvature appear to create larger-scale structures, which lean farther away from the wall, and which exhibit a more regular interface. Time-resolved visualizations using a 500 kHz laser system enable the volumetric reconstruction of the boundary layer’s instantaneous structure.