Do emptying bottles show self-induced liquid rotation?

Abstract

An inverted liquid bottle with a small neck diameter empties through periodic admission of air bubbles at the neck, followed by liquid discharge, a process termed ‘glugging’. In contrast, a large Taylor bubble rises to the air–water interface in the bottle for large neck diameters, followed by an instant interface collapse and a chaotic liquid discharge. We numerically find that a spiral large-scale rotating structure due to churning motion develops in the liquid during time evolution in an emptying bottle, though an initial swirl is not imposed. The induced structure is strong for a large neck bottle, and the circulation strength is maximum near the neck region. The spiral structure’s strength decreases for small neck diameters, and a pure oscillatory ‘glugging’ mode is preserved. The high circulation strength near the neck region for the large neck bottle causes liquid to accelerate and is the reason for the existing empirical models on liquid discharge to deviate from experimental observations.