Abstract
In the present world, passive control finds application in various areas like flow over blunt projectiles, missiles, supersonic parallel diffusers (for cruise correction), the engine of jets, static testbeds of rockets, the ports of internal combustion engines, vernier rockets, and single expansion ramp nozzle (SERN) rockets. In this review, various passive control techniques to control the base pressure and regulate the drag force are discussed. In the study, papers ranging from subsonic, sonic, and supersonic flow are discussed. Different types of passive control management techniques like cavity, ribs, dimple, static cylinder, spikes, etc., are discussed in this review article. This study found that the passive control device can control the base pressure, resulting in an enhancement in the base pressure and reducing the base drag. Also, passive control is very efficient whenever there is a favorable pressure gradient at the nozzle exit.
Highlights
Turbulent base flows are still an active area of research due to their considerable influence on aerodynamic vehicles’ operation and permanency
A base drag reduction of as high as 39% is achieved by employing the splitter plate, whereas, with passive control with spike, the base pressure starts to increase right from the beginning and becomes more than atmospheric pressure at Length to Width ratio (L/W) = 6 to 10, and acquired base pressure values are 5% more than atmospheric pressure
When the passive strategies in the form of ribs, cavities, static cylinder, boattail, and step-body are used, the expansion level plays a crucial role in controlling the base pressure
Summary
Turbulent base flows are still an active area of research due to their considerable influence on aerodynamic vehicles’ operation and permanency. Numerous critical issues impact base flows; a few vital parameters are Mach number, type of boundary layer before the separation, and geometry. Studies were conducted to understand the base flows over an extensive range of flow regimes, subsonic to hypersonic speeds, over the years. Despite these attempts, real insight continues to remain distant. It is realized that the key factors that influence the dynamics of the flow in the base area are the growth of the shear layer and its reattachment, the recirculation region nearby to the base, shedding of the vortex, and the interfaces among them all
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