Computational Study on Base Drag Reduction for a Boat-tailed Axisymmetric Jet Nozzle Through Base Geometry Modifications

A Computational Fluid Dynamics (CFD) analysis was conducted on an axisymmetric boat-tailed afterbody operating at an angle of incidence of zero degrees. The boat-tail drag can significantly affect the performance of overall propulsion system in rockets and missiles. These computations show a very complex regime when the base region flow connects with the flow from the nozzle and the ambient air, with strong adverse pressure gradients and shock induced separations in the flow field. Computations have been carried out at transonic Mach number 0.9 with nozzle pressure ratio (NPR) of 4. The Shear Stress Transport (SST) turbulence model has been used in calculations to study the flow difference in pressure and velocity contours as it provides more accurate results with the data obtained from experiments. Nevertheless, the boat tail surface pressure coefficient for a straight cylinder and a tapered cylinder (or boat tail) has been plotted and analyzed. The boat tail configuration model demonstrated a better performance in terms of drag experienced by the system.