Whirling instability of an eccentric coated fibre

We study a gravity-driven viscous flow coating vertical cylindrical fibre. The destabilisation of draining liquid column into downward moving train beads has been linked to the conjunction Rayleigh–Plateau and Kapitza instabilities in limit small Bond numbers $Bo$ . Here, we focus on quasi-inertialess flows (large Ohnesorge number $Oh$ ) conduct linear stability analysis unidirectional along rigid eccentric fibre for intermediate large show existence two unstable modes, namely pearl whirl modes. mode depicts asymmetric beads, similar that instability, whereas single helix forms axis instability. geometric hydrodynamic thresholds instability are investigated, phase diagrams showing transition between different regimes presented. Additionally, an energy is carried out elucidate formation mechanism. This reveals despite unfavourable capillary cost, interface shear distribution, caused by eccentricity, potential sustain whirling interface. In general, radius eccentricity tend foster while reducing tends favour dominance Finally, compare predictions our model with results some illustrative experiments, using highly silicone oils flowing down fibres. Whirling structures observed first time, measured wavenumbers match prediction.