Control of base pressure for a boat-tailed axisymmetric afterbody via base geometry modifications

An experimental study was conducted to assess the effectiveness of base geometry modifications in controlling the mean and unsteady base pressure development on a circular-arc 12° boat-tailed afterbody at zero angle of incidence under jet-off and jet-on conditions. Tests were carried out for the freestream Mach number range of 0.6 to 1.06 with nozzle pressure ratios for jet-on conditions varying from 1 to 12. Three base geometry configurations, namely, sharp base (or baseline case), rounded base and base cavity were studied. In jet-off condition, relative to the baseline, an increase in coefficient of base pressure by approximately 53% and 42% in the entire Mach number range was observed for the rounded base and base cavity configurations, respectively. Further, in jet-on condition, the rounded base continued to show better performance up to a nozzle pressure ratio of 8 for M∞≤0.9M∞≤0.9. For M∞=1.06M∞=1.06, however, the base cavity is seen to perform much better than the rounded base configuration. With regard to base pressure fluctuations, the base cavity configuration consistently shows maximum reduction in the amplitude that is also accompanied with suppression of high-frequency fluctuations for both jet-on and jet-off conditions.