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SUMMARY:Keynote lecture: Capillary bulldozing and viscously stable frictio
 nal fingers - Bjornar Sandnes (Swansea University)
DTSTART:20230823T123000Z
DTEND:20230823T133000Z
UID:TALK202624@talks.cam.ac.uk
DESCRIPTION:An invading meniscus between two fluids in a Hele-Shaw cell ma
 y bulldoze loose granular material into local compaction fronts. The flow 
 becomes &lsquo\;frictionally unstable&rsquo\;\, and as a result the invadi
 ng fluid becomes shaped into fingers that plough the granular material to 
 the side. In this talk we will see how the competition between friction an
 d capillarity leads to a natural emergent length scale\, the finger width.
  Then\, by increasing viscosity or injection rate\, we gradually amplify t
 he role of viscous forces in the pattern formation. We know from classic f
 luid-fluid displacement that injection of a low viscosity fluid into a hig
 h viscosity fluid produces viscous fingering. The reverse scenario (high v
 iscosity invading fluid) produces compact\, viscously stabilised flow &nda
 sh\; just an expanding disc in a radial Hele-Shal cell. But what happens i
 f we inject a high viscosity fluid into a bed of grains submerged in a low
  viscosity fluid? We inject water/glycerol into hydrophobic grains &ldquo\
 ;submerged&rdquo\; in air. The bulldozing frictional instability generates
  fingers through which a viscous liquid flows. The viscous pressure gradie
 nt depends on injection rate and fluid viscosity\, and we shall see how in
 creasing either produces increased viscous stabilisation of the frictional
  fingering pattern\, taking us through a transition from a single active f
 inger\, to multiple fingers\, and finally to a fully compact &ldquo\;spoke
 &rdquo\; pattern.&nbsp\;
LOCATION:External
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