Capturing the Pinch-Off of Liquid Jets by the Level Set Method

Full three-dimensional dynamic simulations of forced liquid jets flowing into and pinching off in ambient of another liquid were performed by using the level set method for tracking the interface between the immiscible materials. The simulations were performed for jets with viscosity ratios between the inner and outer fluids of 0.17 and 1.7. The jets were forced at Strouhal number of 4.0. The Reynolds, Froud, and Bond numbers based on the conditions at the nozzle exit were 34–35, 0.2, and 6.1, for both cases. The numerical results are compared with the data from the experiment made by Longmire et al. (2001). The comparisons were made for (1) flow images of one complete pinch-off cycle and (2) the axial and radial profiles of the instantaneous velocities around the region of jet disintegration. The feasibility and accuracy of using the level set method in multiphase problems involving interface breakup/coalescence is explored and accessed by simulating such relatively low speed, low density-ratio two-phase flows. Although the level set method is quite promising, due to the surface tension model, it requires very fine grid resolution (the Weber number based on the grid spacing is smaller than $10−2)$ even for capturing the laminar surface phenomena.