Interaction of Second-Mode Disturbances and 3-D Roughness on a Cooled Flared Cone at Mach 6

View Video Presentation: https://doi.org/10.2514/6.2021-1092.vid

The boundary layer on a sharp-tip part-straight, part-flared actively cooled cone has been studied in a quiet Mach 6 wind tunnel. The second-mode instability, which dominates for Mach numbers greater than 4 as a contributor to boundary-layer transition, is the focus of this study. Boundary-layer transition was tracked using embedded thermocouples and a focusing schlieren optical diagnostic. Visualization of the second-mode disturbances was achieved using a high-speed camera and pointwise spectral data taken in the boundary layer using an avalanche photodetector, showing second-mode frequencies ranging from 281 to 315 kHz. Field measurements of the mass flux were acquired using Constant Temperature Anemometry with hot-film probes. Azimuthal sweeps showed periodic mass-flux variations with a wavenumber of 90 which were attributed to Görtler vortices. Distributed Roughness Elements were placed at the neutral point with the same wavenumber seen from the hot-film data to force a 3-D breakdown. This work creates a database for Direct Numerical Simulations and Non-linear Parabolized Stability Equations computations and adds to the current knowledge of hypersonic boundary-layer transition.