Separated flow at a blunt base remains a critical topic in both automotive and aerospace engineering, particularly in the context of high-speed and supersonic vehicles such as modern fighter aircraft. In the separated region, characterized by a recirculation zone, the local pressure is typically lower than the ambient back pressure. This reduced base pressure can account for up to 70 percent of the total drag acting on an axisymmetric body. The present study focuses on regulating the base pressure within the recirculation region to reduce base drag and thereby enhance the operational range of rockets, missiles, and related aerospace vehicles. The analysis considers key inertial and geometric parameters, including a Mach number of M = 1.8, different expansion levels, an area ratio of 6.25, and duct lengths ranging from L/D = 1 to 6. A triangular rib is introduced as a passive flow-control device to modulate the pressure within the duct. In the numerical simulations, the rib base is fixed at 3 mm, while its height varies from 1 mm to 5 mm. The results indicate that increasing the rib height enhances the base pressure, with the largest height producing the greatest pressure rise. A rib height of 3 mm is sufficient to raise the base pressure close to the back pressure. For applications requiring a more substantial increase in base pressure, ribs with heights of 4 or 5 mm are recommended, depending on mission constraints. Optimal performance is achieved when the rib is positioned at L/D = 3 or 4, where the maximum pressure gain is observed.

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.

When better fuel-air mixing in the combustion chamber or a reduction in base drag are required in vehicles, rockets, and aeroplanes, the base pressure control is activated. Controlling the base pressure and drag is necessary in both scenarios. In this work, semi-circular ribs with varying diameters (2, 4, and 6 mm) positioned at six distinct positions (0.5D, 1D, 1.5D, 2D, 3D, and 4D) inside a square duct with a side of 15 mm are proposed as an efficient way to apply the passive control technique. In-depth research is done on optimising rib size for various rib sites. According to this study, the base pressure rises as rib height increases. Furthermore, the optimal location for the semi-circular ribs with a diameter of 2 mm is at 0.5D. The 1D location appears to be optimal for the 4 mm size as well. For the 6 mm size, however, the 4D position fills this function.