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SUMMARY:Simple geometries and unusual (multiphase) flow phenomena - Howard
  Stone\, Princeton University
DTSTART:20140523T150000Z
DTEND:20140523T160000Z
UID:TALK52230@talks.cam.ac.uk
CONTACT:Dr C. P.  Caulfield
DESCRIPTION:We give a few examples of unusual flow phenomena that occur in
 \nrelatively simple geometries. First\, in an introductory\, short survey 
 we\nsketch or briefly illustrate examples with (i) micro patterned substra
 tes\,\n(ii) a variant of the classical Saffman-Taylor viscous fingering\ni
 nstability\, and (iii) an unusual flow effect that occurs for motile but\n
 surface-attached bacteria. Second\, in the main part of the talk we\ndescr
 ibe the seemingly ordinary flow of bubbles moving through a\nT-junction or
  bifurcation. A T-junction is perhaps the most common element in many pipi
 ng systems so it should be expected that the flow structures there are wel
 l understood. In our experiments the flows are laminar but have high Reyno
 lds numbers\, typically Re=100-1000. For a two-phase flow in this geometry
  it seems obvious that any particles in the fluid that enter the T-junctio
 n will leave following the one of the two main flow channels. Nevertheless
 \, we report experiments that document that bubbles and other low density 
 objects can be trapped at the bifurcation. The trapping leads to the stead
 y accumulation of bubbles that can form stable chain-like aggregates in th
 e presence\, for example\, of surfactants\, or give rise to bubble growth 
 due to coalescence. Our three-dimensional numerical simulations of the cor
 responding single-phase flow rationalise the mechanism behind this phenome
 non and highlight unrecognized richness of the three-dimensional flow at t
 he T-junction.
LOCATION:MR2\, Centre for Mathematical Sciences\, Wilberforce Road\, Cambr
 idge
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