Boundary-Layer Instabilities on Variable Bluntness Cones with Outgassing in Hypersonic Quiet Flow

Experiments were executed to investigate the effect of ablative outgassing on boundary-layer instabilities on a slender cone in Mach 6 quiet flow. A [Formula: see text] half-angle cone with solid and porous nose tips was tested. The porous nose tips were of varying bluntness: nominally sharp, [Formula: see text], and [Formula: see text]. The permeability of each nose tip was measured using a modified ISO standard, and the outflow was measured using miniature hot-wire anemometry. The model was instrumented with surface pressure transducers and an atomic layer thermopile, and high-speed schlieren was used to visualize the boundary layer. Experiments were done in the Boeing/AFOSR Mach 6 Quiet Tunnel at Purdue University at approximate Reynolds numbers of [Formula: see text] and [Formula: see text] and with varying blowing rates. Without blowing, bluntness suppressed the second-mode instability. In all cases, blowing advanced transition upstream. On the sharp cone and the [Formula: see text] geometry, second-mode instabilities were the dominant transition mechanism. With the [Formula: see text] nose tip installed, second-mode waves were not observed. However, blowing advanced transition, and a 40 kHz instability dominated laminar-to-turbulent transition on the [Formula: see text] geometry.