Air entrainment induced by vorticity-free-surface interaction

The free surface dynamics induced by a rising vortex pair is here numerically investigated through a two-fluids Navier-Stokes solver coupled with a Level-Set technique for the interface capturing. Surface tension effects are modelled in the form of a continuum force acting on a small neighbourhood of the interface. The numerical model is applied to simulate the motion of a viscous vortex pair rising toward the free surface leading to a strong vorticity?free-surface interaction. A careful validation of the present two-fluids numerical approach is carried out for a gentle rising vortex, recovering single-fluid results available in literature obtained by using moving grid technique. When the same flow is simulated for higher Froude numbers a much larger free surface distortion takes place, eventually giving rise to the entrainment of an air bubble which significantly change the dynamics of the primary vortex. The Weber number is found to play an important role on that respect as well.