  As the liquid jet plunges into a free surface, significant air is entrained
into the water and forms air pockets. These air pockets eventually break up
into small bubbles, which travel downstream to form a bubbly wake. To better
understand the underlying flow physics involved in the bubble entrainment, in
the linked videos, air entrainment due to a water jet plunging onto a pool of
stationary water was numerically studied by using the 3DYNAFS software suit.
  The flow field is simulated by directly solving the Navier-Stokes equations
through the viscous module, 3DYNAFS-VIS, using a level set method for capturing
the free surface. The breakup of entrained air pockets and the resulting bubbly
flow were modeled by coupling 3DYNAFS-VIS with a Lagrangian multi-bubble
tracking model, 3DYNAFS-DSM (Hsiao & Chahine, 2003), which emits bubbles into
the liquid according to local liquid/gas interface flow conditions based on the
sub-grid air entrainment modeling proposed by Ma et al. (2011), and tracks all
bubbles in the liquid flow using equations of motion and bubble dynamics.
Further breakup of the dispersed bubbles into smaller ones is modeled by
incorporating the bubble breakup model developed by Martinez-Bazan et al.
(1999). The software was parallelized by using a hybrid MPI-OpenMP scheme.
  The video describes the impinging of a water jet with a diameter of 4 cm at a
velocity of 4 m/s, the entrainment and breakup of the air pockets accompanied
by strong production and interaction with vorticity structures, and the
subsequent bubbly flows. This video has been submitted to the Gallery of Fluid
Motion 2011, which is an annual showcase of fluid dynamics videos.
