Numerical study of 3-D air core phenomenon during liquid draining

An air core is the vortex flow generated when rotating liquid in a tank drains into a narrow drain port. In various industrial areas, the air core often causes adverse effects, such as unwanted air entrainment or a reduced drain flow rate. The air core phenomenon has largely been simulated with a 2-D axisymmetric flow assumption. In this study, a 3-D numerical simulation of the liquid draining from a cylindrical tank was conducted. The results were compared with previous experimental and 2-D simulation results. Based on the present 3-D simulation results, as an air core generation mechanism, the interaction between the axially and circumferentially rotating vortex structures was suggested. Additionally, 3-D flow structures such as toroidal Taylor vortex rings and spiral waves on free surfaces, which could not be obtained in 2-D simulations, were successfully reproduced.