Drag reduction of axisymmetric boattail models by a combination of base bleed and groove cavities

Base drag can constitute up to 50% of the total aerodynamic drag of axisymmetric vehicles with blunt bases, such as submarines, missiles, artillery shells, and aircraft. Different techniques for reducing drag, including the boattail, groove cavities, and base bleed, have been studied. However, they have typically been investigated independently. This study examines the combined influence of these three methods on drag reduction for an axisymmetric three-dimensional model operating under subsonic flow conditions. The generalized k–ω turbulence model, based on the k–ω SST formulation with adjustable coefficients, is employed to enhance simulation accuracy. The freestream velocity is fixed at U∞ = 156 m/s, while the parameters related to the boattail and base bleed are varied. The corresponding Mach number is 0.463. Specifically, the boattail slant angle β ranges from 0° to 24°, and the injection coefficient is changed between 0 and 0.1231. Longitudinal groove cavities are also generated on the surface to find the techniques for effective drag reduction in a wide range of boattail angles. The simulation results are consistent with experimental observation. Results indicate that the base bleed is mainly effective in reducing drag for low boattail angles, while groove cavities are effective for high boattail angles. By applying base bleed and groove cavities, the drag is found to be reduced between 15% and 44% for boattail angles in the range tested. The mechanisms for drag reduction, including wake flow, drag components, turbulent kinetic energy, and mixing layer characteristics, are discussed in detail.