  Experimental studies are carried out to investigate the effects of the
geometrical parameters with a drag reducing spike on a hemispherical forebody
in a supersonic freestream of $M_\infty=2.0$ at $0^{\circ}$ angle of attack.
The spike length $(l/D=0.5,1.0,1.5,2.0)$, spike stem diameter
$(d/D=0.06,0.12,0.18)$, and spike tip shapes are varied and their influence on
the time-averaged, and time-resolved flow field are examined. When $l/D$
increases, a significant reduction in drag ($c_d$) is achieved at $l/D=1.5$,
whereas the variation in $d/D$ has only a minor effect. The intensity of the
shock-related unsteadiness is reduced with an increase in {$d/D$ from $0.06$ to
$0.18$}, whereas changes in $l/D$ have a negligible effect. The effects of
spike tip geometry are studied by replacing the sharp spike tip with a
hemispherical one having three different base shapes (vertical base, circular
base, and elliptical base). Hemispherical spike tip with a vertical base is
performing better by reducing $c_d$ and flow unsteadiness. The dominant
Spatio-temporal mode arising due to the shock-related unsteadiness is
represented through modal analysis of time-resolved shadowgraph images and the
findings are consistent with the other measurements.
