Passive control of base drag with d-shaped rib in a suddenly expanded flow

The sudden increase in area at the blunt base of rockets, missiles, projectiles, and automobiles is widespread. The sudden rise in the base area leads to flow separation and reattachment, and the pressure in the separated recirculation zone is lower than the ambient pressure. In this study, a passive control in the form of a D-shaped rib is suggested to control the base pressure and, hence, the base drag, which is considerable at the critical Mach numbers. The present study aims to regulate the base pressure using D-shaped ribs of various heights and radii at sonic Mach numbers. The duct diameter and length-to-diameter (L/D) ratios were from 1 to 6, and rib locations were considered at L/D = 0.5, 1, 1.5, 2, and 3. When the rib has orientation 2, and the shear layer faces the straight part of the rib, the base pressure's magnitude is higher than in orientation 1. It is seen that with a 1 mm rib as a control mechanism, the base pressure attains a value more than ambient pressure. Hence, if the user must equate the base pressure with atmospheric pressure, then a 1 mm rib radius at L/D = 1 is the right choice. If it is required to raise the base pressure by a considerable value, then higher values of rib radius are to be considered