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.