Axial instability in liquid entrainment

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Abstract
We investigate the emergence of patterns as liquid is entrained along the exterior surface of a partially immersed cylinder rotating around its horizontal axis. Our findings reveal that the coating flow exhibits marked axial variations, leading to the formation of a series of nearly vertical, slender liquid structures whose shape and location fluctuate over time. Measurements indicate that the spacing between these liquid ribs depends only weakly upon velocity, viscosity, or confinement conditions around the cylinder. Additionally, direct numerical simulations (DNS) successfully captured the experimentally observed behavior and the values of the associated wavelength. We discuss suspected mechanisms for the instability: a Saffman–Taylor instability, where the pressure gradient building within the extracted liquid film drives the instability; or a Rayleigh–Taylor instability driven by gravity. Both mechanisms predict the right order of magnitude for the spacing of the ribs, controlled by the capillary length.
Funding Information
  • LABEX iMUST (ANR-10-LABX-0064)

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