Control of Mach number 6 sharp cone boundary-layer transition using wall blowing

This study aimed to investigate the influence of wall blowing on the instability mechanisms that induce boundary-layer transition over a 7° half-angle cone in a Mach number 6 flow. Experiments were conducted in a ∅=0.6 m Ludwieg tube using CO 2 -enhanced filtered Rayleigh scattering flow visualization, fast-response pressure sensors, infrared thermal imaging, and particle image velocimetry. The sharp cone model, approximately 500 mm in length, features a 100 mm long injection zone located 190 mm downstream of the apex. Air was injected at non-dimensional blowing ratios F (the ratio of mass flux between the injection gas and the free stream) of 0, 0.056%, 0.28%, and 0.63%. Results indicate that increasing the blowing ratio leads to gradual thickening of the boundary layer downstream of the injection location and promotes boundary-layer transition. Moreover, as F increases, the frequency of the instability waves decreases, while their phase speed increases. At a low blowing ratio (0.056%), the boundary-layer transition is primarily governed by the Mack second modes. However, at a high blowing ratio (0.63%), a low-frequency disturbance with a peak frequency of approximately 63 kHz emerges, driving boundary layer breakdown and likely originating from shear layer instability. These experimental results provide new insights into the effects of wall blowing on high-speed boundary layer instability.