Drag reduction of afterbodies by controlled separated flows

The zero-lift drag characteristics of a class of multistep afterbodies that utilize the concept of controlled separated hows are documented at transon ic and supersonic speeds. The important geometrical and flow parameters aff ecting the drag of such afterbodies are identified, and their effects are e xamined through a parametric study. The results show that multistep afterbo dies can be designed that provide significant total drag reduction (as high as 50%) compared to (unmodified) blunt bases; however, compared to axisymm etric boattailed afterbodies of a given base area, the multistep afterbodie s have relatively higher drag. Finally, the certain flow features involving separation and reattachment on multistep afterbodies are discussed based o n flow visualization studies.