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SUMMARY:Instability to elastic turbulence\; freezing soft particles\; conf
 ined viscous flows - Miguel Beneitez\, Pallav Kant\, Ashleigh Hutchinson -
  DAMTP
DTSTART:20221021T150000Z
DTEND:20221021T160000Z
UID:TALK182945@talks.cam.ac.uk
CONTACT:Prof. Jerome Neufeld
DESCRIPTION:Miguel Beneitez - Linear instability leading to elastic turbul
 ence in plane Couette flow\n\nIt is known that a simple\, Newtonian fluid 
 may experience transition to turbulence in the presence of inertia. In con
 trast\, viscoelastic fluids\, solutions of flexible long-chain polymers\, 
 have been shown to exhibit chaotic dynamics even in the absence of inertia
 \, entirely sustained by its elastic properties. The origin of such 'elast
 ic turbulence' has often been linked to a linear instability of curved str
 eamlines. In this talk\, we present a new viscoelastic rectilinear instabi
 lity in one of the most fundamental flow configurations\, plane Couette fl
 ow. This instability\, found in the inertialess limit\, stems from a finit
 e polymeric diffusion\, caused by the molecular diffusion of the polymer c
 hains\, and relies on a novel instability mechanism. We perform the first 
 numerical simulation of the nonlinear evolution of the associated eigenmod
 es and we show that it leads to self-sustained elastic turbulence in paral
 lel flow.\n\nPallav Kant - Interaction of soft particles with moving solid
 ification front\n\nFreezing of dispersions is omnipresent in science and t
 echnology. While the passing of a freezing front over a solid particle is 
 reasonably understood\, this is not so for soft particles. In the present 
 investigations\, using an oil-in-water emulsion as a model system\, we sho
 w that when engulfed into a growing crystal\, a soft particle severely def
 orms\, even forming pointy-tip shapes in extreme situations. We show that 
 such singular deformations are mediated by interfacial flows in nanometric
  thin liquid films separating the non-solidifying dispersed droplet and th
 e solidifying bulk. We model the fluid flow in these intervening thin film
 s using a lubrication approximation and then relate it to the deformation 
 sustained by the dispersed droplet.\n\nAshleigh Hutchinson - The evolution
  of a viscous gravity current in a confined geometry\n\nThe aim of this ta
 lk is to present a theoretical and experimental study of an axisymmetric v
 iscous gravity current with a constant flux confined to the space between 
 two horizontal parallel plates. The effect of confinement is to produce tw
 o regions of flow: an inner region where the fluid is in contact with both
  plates and an outer annular region where the fluid forms a gravity curren
 t along the lower plate. I will outline a simple theoretical model that de
 scribes the flow dynamics by a single dimensionless parameter which is the
  ratio of the characteristic height of an unconfined gravity current to th
 e height of the confined space. Theoretical height profiles display the sa
 me characteristics as unconfined gravity currents until this ratio reaches
  approximately a half\, where a rapid change in behaviour occurs as confin
 ement comes into effect. For larger values of this ratio\, the confined vi
 scous gravity current gradually tends to Hele-Shaw flow\, with the transit
 ion essentially complete by a value of 2. The findings from the theoretica
 l model are compared to the results of a series of experiments using golde
 n syrup with various fluxes and gap spacings. Although the data aligns wit
 h the major aspects of the model\, it is clear that other physics is at pl
 ay and a single non-dimensional parameter is not sufficient to capture the
  flow behaviour fully. Possible mechanisms that may be responsible for thi
 s mismatch will be briefly discussed.
LOCATION:MR2\, Centre for Mathematical Sciences\, Wilberforce Road\, Cambr
 idge
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