Oblique breakdown for a blunt cone at Mach 6 : The effect of nose bluntness on high-speed boundary-layer transition is a topic of great scientific and practical importance. While it is known that nose bluntness stabilizes the boundary layer based on linear stability theory, it has been observed that in so-called “conventional” or noisy wind tunnels the transition location can suddenly move upstream beyond a threshold nose bluntness (transition reversal). Although this phenomenon was observed first over 3 decades ago it is still not fully understood what causes transition reversal. In addition to having a stabilizing effect on the boundary layer nose bluntness also gives rise to a new instability, the so-called entropy layer instability. The results above shows how transition can be initiated on a blunt cone just downstream of the nose by forcing a pair of oblique waves in the entropy layer. The contours above how how disturbance waves (temperature perturbations) propagate along the entropy layer and grow in amplitude until they contaminate the boundary layer and subsequently lead to rapid laminar-turbulent boundary layer transition. The isosurfaces of the Q- vortex identification criterion colored with temperature disturbance contours display the various breakdown stages of a high-speed boundary layer form laminar all the way to turbulent flow. Contributors: Andrew Hartman, Christoph Hader, Hermann Fasel