Air entrainment by a plunging jet under intermittent vortex conditions
  This fluid dynamic video entry to the 2011 APS-DFD Gallery of Fluid Motion details the transient evolution of the free surface surrounding the impact region of a low-viscosity laminar liquid jet as it enters a quiescent pool. The close-up images depict the destabilization and breakup of the annular air gap and the subsequent entrainment of bubbles into the bulk liquid. 
Kevin Jin Kim, Kyle Corfman, Kevin Li, Ken T. Kiger
physics.flu-dyn physics.ao-ph