Techniques for application of roughness for manipulation of second-mode waves on a flared cone at Mach 6

Abstract

Experimental validation of physics-based transition models is essential to improving the state of the art of hypersonic vehicle design. This research focuses on one aspect of this problem, which is the effect of surface roughness on the non-linear breakdown of second-mode waves in hypersonic boundary layers. A flared cone was designed to allow non-linear growth of second-mode waves to sufficient amplitudes to lead to transition under quiet flow in the Boeing/AFOSR Mach 6 Quiet Tunnel. The non-linear breakdown process is characterized by a set of streamwise streaks of increased heating, followed by the onset of turbulence. The location of the streaks is related to small amounts of upstream surface roughness. Techniques for applying and fabricating surface roughness were developed. These are to be used to manipulate this breakdown process. While certain types of roughness have been used to introduce streamwise vorticity in other flows at low speeds, it was unknown what types of roughness would work in the present case. The effects of the new roughness types were analyzed through pressure measurements and global heat transfer visualization using temperature sensitive paint. None of the new roughness types was able to directly control the spanwise periodicity of the streaks, but two types were identified as good candidates for future testing. More work is required to develop a suitable technique for fabricating and applying small roughness