Leading-Edge Bluntness Effect on Intermittency in Hypersonic Boundary Layer Transition Over a Slender Cone

The temporal intermittency of turbulent spots in high-speed boundary layers is well documented, whereas the intermittency of the Mack-mode instability wave packets that precede spot formation has received relatively limited attention. This study investigates the joint intermittency behavior of Mack-mode disturbances and turbulent spots over a 7-deg half-angle cone with sharp and blunt (0.5 mm radius) nose tips in a Mach 6 freestream. Pulse-burst schlieren visualization on the sharp cone reveals intermittent switching among three distinct states: laminar flow, second-mode-dominated intervals, and turbulent spots. Temporally local frequency spectra enable the dynamics of these states to be inferred. In contrast, the blunt cone exhibits strong suppression of second-mode growth and the emergence of elongated low-frequency disturbances, with only weak and sporadic Mack-mode activity being visible. Wall-pressure measurements are used to quantify the intermittency of both Mack-mode disturbances and turbulent spots. The results showed a clear progression—increasing Mack-mode intermittency in the early transition region, saturation prior to breakdown, and a downstream rise in turbulent-spot intermittency approaching towards a fully turbulent flow. Burst-rate and average-burst-length trends are used to further characterize the growth and evolution of Mack-mode wave packets and turbulent spots. Together, these findings provide a more unified view of instability-wave and turbulent-spot intermittency in hypersonic boundary layer flow transition.