Breakdown of boundary layer instabilities on a straight cone in a hypersonic shock tunnel

Experimental investigations of the second-mode dominated hypersonic laminar-turbulent transition process in hypervelocity flow were carried out using a 7∘ half-angle, straight cone with moderate bluntness at zero angle of attack. The tests were conducted at Mach 7.4 in the High Enthalpy Shock Tunnel Göttingen (HEG) of the German Aerospace Center (DLR). Two different nose tips were used resulting in a Reynolds number based on the nose radius of Ren≈5100 and Ren≈10200. Surface thermocouples, temperature sensitive paint (TSP) and fast-response piezoelectric pressure transducers were used to characterize the transition process. Strong second-mode waves were measured far downstream of the nose tip followed by the appearance of streamwise-oriented streaks of high surface heat flux. Similar streak patterns were observed on flared cones under quiet flow conditions in the Boeing/AFOSR Mach 6 Quiet Tunnel at Purdue University. The present measurement of the primary instability and the spatiotemporal evolution of the streaks represent the first test case reported from a conventional shock tunnel at flight enthalpies and with a highly cooled wall.