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  4. Dynamics of falling films on the outside of a vertical rotating cylinder: waves, rivulets and dripping transitions
 
research article

Dynamics of falling films on the outside of a vertical rotating cylinder: waves, rivulets and dripping transitions

Rietz, Manuel
•
Scheid, Benoit
•
Gallaire, Francois  
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2017
Journal of Fluid Mechanics

Falling liquid films on the underside of a plate or on the outside of a rotating cylinder are subject to a destabilizing body force. The evolution of the film topology is determined by interactions between the Kapitza and the Rayleigh-Taylor instability, leading to complex patterning of the film surface and eventually fluid detachment from the substrate. This study experimentally investigates the evolution of the surface topology for a film on the outside of a vertical rotating cylinder of large radius. Shear at the liquid/air interface is suppressed through an outer, co-rotating cylinder. The film evolution is captured through high speed visualization in dependence of the control parameters, namely Reynolds number and rotation frequency. An increasing influence of the Rayleigh-Taylor instability for an increasing destabilizing body force (increasing rotational speed of the cylinder) is most notably observed in the form of a decreasing inception length of rivulet structures dominating the film topology. Wavelength as well as inception length of rivulets match the predictions from linear stability analysis of the classical Rayleigh-Taylor problem. In this context, experimental and supporting numerical results suggest that the emergence of rivulets occurs for any non-zero value of the destabilizing body force after a given evolution length that decreases with increasing body force. Fluid detachment from the substrate is found to be intimately related to the existence of rivulet structures. In dependence of the control parameters, detaching droplets are either observed as a result of interactions of solitary pulses of varying phase speed on rivulets, directly after destabilization of two-dimensional waves into rivulets or immediately at the fluid inlet. By comparison to the convective/absolute instability transition predicted by linear stability analysis of an integral boundary layer formulation of the problem in question, it is shown that the prediction of a predominant dripping mechanism lies beyond the scope of linear analysis.

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Type
research article
DOI
10.1017/jfm.2017.657
Web of Science ID

WOS:000413857000001

Author(s)
Rietz, Manuel
Scheid, Benoit
Gallaire, Francois  
Kofman, Nicolas
Kneer, Reinhold
Rohlfs, Wilko
Date Issued

2017

Publisher

Cambridge University Press

Published in
Journal of Fluid Mechanics
Volume

832

Start page

189

End page

211

Subjects

instability

•

low-Reynolds-number flows

•

waves/free-surface flows

Editorial or Peer reviewed

REVIEWED

Written at

EPFL

EPFL units
LFMI  
Available on Infoscience
November 8, 2017
Use this identifier to reference this record
https://infoscience.epfl.ch/handle/20.500.14299/141953
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