Base Flow Control through Bullet-Shaped Ribs at Mach 1.6

The rapid development of space transportation systems and high-speed military aircrafts have intensified interest in turbulent separated flows, particularly under transonic and supersonic conditions. Such flows commonly arise downstream of sudden expansions, where separation and subsequent reattachment generate strong shear layers, increased drag, and a low-pressure recirculation region at the base. In this study, the control of base pressure downstream of a sudden expansion is investigated numerically using a passive bullet-shaped rib. A jet issuing from a nozzle is discharged abruptly into a duct of 25 mm diameter, producing a separated flow with pronounced recirculation. Bullet-shaped ribs with length-to-diameter ratios ranging from 0.5 to 3 are placed at different axial locations, and three rib geometries are examined. The results indicate that ribs with L/D = 0.5 are largely ineffective for two of the geometries, whereas the third geometry produces a substantial increase in base pressure. For rib placements at L/D ratios of 1, 1.5, and 2, geometries corresponding to cases 1 and 2 do not significantly alter the flow, as reattachment occurs farther downstream. In contrast, the rib geometry of case 3 consistently enhances base pressure across all tested locations, with the most pronounced improvements observed when the rib is positioned at L/D = 2 and 3.