Control of Base Pressure in Supersonic Separated Flows over Axisymmetric Bodies Using Triangular Rib Actuators

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.