SIMULATION OF AIR ENTRAPMENT BY A PLUNGING LIQUID JET OF FINITE LENGTH

摘要

The impingement of a finite length round water jet on a large pool of water was simulated numerically using a 3D Eulerian-Lagrangian Marker and Micro-Cell (ELMMC) method. The method allowed simulation of the initial impact of the jet on the pool surface, the deformation of the pool surface by the falling jet, and, under certain conditions, the entrapment of an air bubble as the pool closes in on the jet. The conditions considered were for ratios of jet length to radius (h/r) in the range of 4 to 25 and jet Froude number in the range of 16 to 74. The results agreed with previous experimental observations by Oguz et al. (J. Fluid Mech., 294, 1995) in terms of entrapped air volume and the possible geometries of entrapped bubbles (viz., toroidal or spheroidal). The simulation results also allowed for a detailed study of effects difficult to discern experimentally, such as vorticity generation and differences in entrapped air volume between toroidal and spheroidal bubbles.