Figure 1.

The computational setup for the plug propagation and rupture. The plug moves from left to right due to applied pressure difference $\Delta p^{*}=p_1^{*}-p_2^{*}$. The arclength (s*) is measured from the centerline in the clockwise and counterclockwise directions for the leading and trailing air fingers, respectively. Note that the arclength of the trailing air finger is made negative to distinguish it from that of the leading air finger. When the liquid plug ruptures, a negative arclength denotes a point on the interface whose axial location z_p is smaller than the axial location of the rupture point z_rupture.