Review of Active and Passive Devices for Drag Reduction

Base drag accounts for up to 40% of the total aerodynamic drag experienced by aerodynamic bodies like projectiles, missiles, and rockets, significantly reducing their range and aerodynamic performance. This paper reviews 36 scientific research papers exploring active and passive methods of base drag reduction. It considers active methods, such as base bleed and external burning, and passive methods, which include boattailing, cavitation, and passive porosity to understand their effectiveness in base drag reduction. Active methods like base bleed and external burning work by injecting additional mass or fuel into the base flow, influencing the flow pattern in the recirculation region. Active methods have some downsides, including an increase in the overall weight of the projectile and a higher fuel consumption rate, which impacts the projectile’s performance and efficiency. On the other hand, passive methods aim to reduce drag through modifications in the shape or structure of the projectile itself. They work by enhancing the base pressure of the projectile, which, in turn, reduces the base drag. The review includes an analysis of three different flow regimes—transonic, supersonic, and subsonic. The papers reviewed modified aerodynamic bodies with different active and passive methods, evaluating their impacts on each of the flow regimes. In transonic flow, the base pressure distribution pattern is affected by phenomena like drag divergence. Besides boattailing and cavitation, the reviewed papers found methods like passive porosity effective in reducing base drag. However, the studies found a combination of passive porosity in boattailed geometry as most effective in drag reduction in the transonic flow regime. In supersonic flow, the papers reviewed studied passive methods like boattailing and cavitation for reducing drag, in which boattailing was found to be the most effective in drag reduction. In hypersonic flow, the reviewed research showed no significant link between cavitation and drag reduction in the hypersonic regime. While a fin configuration increased drag with higher Mach numbers and angles of attack, the use of a counter jet flow mechanism with an aerospike was found to significantly aid drag reduction.