Influence of wind on a viscous liquid film flowing down a thread

TL;DR

This study experimentally examines how side-wind influences the stability, flow speed, and pattern formation of a viscous liquid film flowing down a thread, revealing wind-induced regime shifts and pattern irregularities.

Contribution

It provides new insights into wind effects on viscous film dynamics, including flow acceleration and pattern instability, which were not previously characterized.

Findings

Wind reduces viscous dissipation, increasing slide speed.

Side-wind causes beads to shift downstream, breaking symmetry.

Wind can induce a transition from regular to irregular bead patterns.

Abstract

We investigate experimentally the effect of wind on the dynamics of a viscous liquid film flowing down a thread. The liquid film is well-known to destabilize into an axisymmetric bead-like pattern in stagnant air. When the flowing film is exposed to side-wind, the beads are pushed downstream breaking the symmetry leading to a modification of the film flow. The viscous dissipation in the liquid film decreases with increasing side-wind, leading to a faster slide speed of the liquid beads. The inertia in the film is then increased, which can induce a regime shift, triggering an instability. When the film becomes unstable, it switches from a periodic pattern of equally sized liquid beads to an irregular film pattern where large beads collide with smaller ones.