Direct Numerical Simulations of Hypersonic Boundary-Layer Transition for a Straight Cone at Mach 7

Direct Numerical Simulations (DNS) were carried out to investigate the laminar-turbulent transition process for a straight (right) cone with blunted nose tips and a 7^◦ opening half-angle at Mach 7 and zero angle of attack. The cone geometry of the experiments in the High Enthalpy Shock Tunnel (HEG) of the German Aerospace Center (DLR) in Göttingen was used for the numerical investigations. Two different nose radii were considered. Investigations of the linear stability regime showed a region of significant second-mode amplification far downstream of the nose tip of the cone. Secondary instability calculations revealed the possibility of a strong fundamental resonance and indicated that secondary waves with a large range of azimuthal wavenumbers can lead to strong resonance (large growth rate after resonance onset). Highly-resolved DNS of a so-called fundamental breakdown were carried out using disturbance generation parameters as determined from primary and secondary instability investigations. For both nose radii, the development of so-called “primary” streaks was observed. Similar streak patterns have also been observed in the Purdue flared and slender cone experiments in the Purdue quiet tunnel and in our previous numerical investigations using DNS.