We also investigated the aerodynamic characteristics
of a smooth sphere, in order to verify the wind
tunnel set-up used in this study. The sub-critical and
super-critical Cd values of a smooth sphere are
reported to be ~0.5 and ~0.1, respectively. Moreover,
the critical Reynolds number (Recrit) value at which the
boundary layer shifts from laminar to turbulent is
reportedly ~3.5 × 105 (Achenbach, 1972). Using the
wind tunnel set-up described above, the sub-critical
and super-critical Cd values of a smooth sphere were
found to be ~0.45 and ~0.1, respectively (Fig. 3). The
Cd values of the sub-critical regime in this study were
slightly smaller than the values reported by Achenbach
(1972). The Cd values of the super-critical regime in
this study were similar to those reported by
Achenbach (1972). The Recrit value of the smooth
sphere produced using this experimental set-up was
~3.5 × 105, which was similar to the value reported by
Achenbach (1972). Therefore, we considered the
experimental data generated using the wind tunnel
set-up in the current study to be suitable for further
investigations.