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

This is the authors' abstract. We don't add key points for this paper.

• In an experimental investigation of a transitional boundary layer on a straight cone in a hypervelocity hypersonic free-stream, primary instabilities were found to reach saturation. • Downstream of this saturation, measurements in the nonlinear region of the boundary layer revealed the presence of streamwise streaks in the near-wall region • These measurements are novel, in that they investigate these streamwise streaks for the first time in a conventional shock tunnel under flight-relevant high enthalpy conditions • In-depth examination and quantification of the streamwise streaks found them to be dependent on nose radius and the extent of development of the transition process. • These measurements present a test case for the improvement of direct numerical simulations for physics-based modelling of transition. 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 R e n ≈ 5100 and R e n ≈ 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.