Nose-Tip Transition Control by Surface Roughness on a Hypersonic Sphere

Abstract

The surface heat flux on a 100 mm diameter hypersonic sphere was reduced through surface roughness on its forebody. The test model was subjected to a hypersonic freestream of Mach 8.8 and Reynolds number 1.98 million/m, in a shock tunnel. Forebody surface heat transfer rates measured on smooth and rough spheres, under the same free-stream conditions, were compared. The comparison of heat flux indicated an overall reduction in surface heating rates on the rough model, which could be attributed to the delayed nose tip transition. The surface roughness on the forebody of the model generated miniature cavities. Stability of the free shear layer over the miniature cavities and entrapment of the destabilizing vortices in the cavities, make the flow over the rough test model more stable than the attached boundary layer over the smooth model, under transitional conditions.