Underwater bubble pinch-off: transient stretching flow

TL;DR

This paper reveals that during underwater bubble pinch-off, transient vertical flows develop rapidly, significantly influencing the shape evolution of the collapsing bubble neck, contrasting with previous assumptions of purely radial flow.

Contribution

The study demonstrates that transient vertical flows emerge during bubble pinch-off, altering the collapse dynamics and shape evolution, which was not accounted for in earlier models assuming radial flow.

Findings

Vertical flows develop rapidly during pinch-off.

Vertical flows influence the shape and symmetry of the collapsing neck.

Transition to slender, symmetric shape occurs faster than previously thought.

Abstract

At the point of pinch-off of an underwater air bubble, the speed of water rushing in diverges. Previous studies that assumed radial flow throughout showed that the local axial shape is two smoothly connected, slender cones that transition very slowly (logarithmically) to a cylindrical segment. Our simulations show that even with initially radial flow, a transient vertical flow develops with comparable speeds. Bernoulli pressure draws water into the singularity region while incompressibility forces it away from the neck minimum, generating significant vertical flows that rapidly slenderize and symmetrize the collapse region. This transition is due to a different mechanism, occurring much faster than previously expected. Vertical flows dictate the neck shape evolution.