Angle-of-Attack Effects on Hypersonic Transitional Shock-Wave/Boundary-Layer Interactions over ROTEX-T

Angle-of-attack (AoA) effects on hypersonic transitional shock-wave/boundary-layer interactions (SWBLIs) were investigated using a 39% scale ROTEX-T cone–flare in the AFOSR–Notre Dame Large Mach-6 Quiet Tunnel at freestream unit Reynolds numbers of 5.8 million/m–10.0 million/m under conventional noise conditions. Prior zero-AoA results showed that an upstream laminar boundary layer convecting instability waves separates upstream of the cone–flare junction, feeding a transitional bubble that hosts absolute instabilities. The combined effect of convective and strong global instabilities led to profound discrepancies between laminar/turbulent computed base flows and experimental results, even when compared to direct numerical simulations that included inflow disturbances. Non-zero AoA further complicates this already intricate flow. The SWBLI was investigated using simultaneous infrared thermography, ultra-high-speed schlieren imaging (1.2 million frames per second), and high-frequency pressure transducers, providing global, time-resolved measurements of both the mean and unsteady flow. Analysis of the mean flow revealed that peak heating on the flare occurs on the windward side, coinciding with a larger separation bubble, while the leeward side exhibits lower heating and a shorter separation length, independent of Reynolds number. High-frequency surface and off-wall measurements captured global unstable modes and convective instabilities corresponding to Mack’s first and second modes. Transition to turbulence was strongly tied to the reattachment location, and the downstream breakdown of instabilities exhibited limited dependence on Reynolds number and AoA. While slight AoAs (approximately 1 degree) do not modify the underlying transition mechanisms, they do produce significant shifts in both the transition location and breakdown distance.