Liquid ligament formation dynamics on a spinning wheel

• Liquid disintegration on a spinning wheel atomizer was investigated experimentally.
• Velocity slip between liquid film and wheel surface only significant at slow rotation.
• As a ligament grows, the trajectory of its free end resembles an involute.
• Maximum ligament length is proportional to the liquid flow rate and viscosity.
• Significant effect of end pinch-off on ligament strain rate and breakup mechanism.

A ligament-type disintegration of liquid on a spinning wheel was investigated experimentally using photographs taken by a high-speed camera. Three different Newtonian liquids were used at various flow rates and the wheel rotational speed was varied in a wide range. Velocity slip between the liquid film and the wheel surface was found to depend primarily on wheel rotational speed and angular position, dropping to approximately 1–1.5% for sufficiently fast rotation. As a liquid ligament grows from the film, the relative pathline of its free (head) end resembles an involute. Ligament strain rate on the film was found to increase steadily until the head droplet pinch-off when a short but significant strain rate reduction was observed. At this point, ligament is rapidly decelerated in the lateral direction which may cause significant longitudinal oscillations, possibly destabilizing its growth. Strain rate then increases again until the ligament detachment from the film which is soon followed by capillary breakup into droplets. The mean ligament length at detachment was determined to increase with a rising liquid flow rate and Ohnesorge number.