Experiment of the two-dimensional roughness effect on hypersonic boundary-layer transition

An experimental investigation of the effects of two-dimensional roughness on hypersonic boundary layers was carried out at the JAXA 0.5 m hypersonic wind tunnel using a 5 deg half-angle sharp cone at a freestream Mach number of 7.1 and a wide range of stagnation conditions. Aerodynamic heating distributions and surface pressure fluctuations were measured with and without roughness elements applied to the cone. A wavy wall roughness with a wavelength of 2 delta located well upstream of the breakdown region had the effect of delaying transition. Surface pressure spectrum densities indicate that disturbances of the roughness wavelength are amplified compared to the smooth wall case. At a lower stagnation temperature, however, wavy wall roughness configurations had the same effect as regular roughness, and no discernible differences between wavy wall roughness and spherical roughness were observed, either in the transition point or in the pressure fluctuation spectrum.