Modeling air entrainment in plunging jet using 3DYNAFS

Abstract: 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.