Looping Network Meetings

#47 February 5, 2024

Monday, 15:00 CET

Bjornar Sandnes

Pattern formation in frictional fluids

Abstract:
An invading meniscus in a Hele-Shaw cell may bulldoze loose granular material and become ‘frictionally unstable’. In this talk we shall see that this frictional instability combined with viscous and compressibility effects sets the stage for a wonderful variety of flow patterns. Frictional fingers, capillary fracturing, stick slip bubbles and more. We shall focus on the role of viscous pressure: We know from classic fluid-fluid displacement that injection of a low viscosity fluid into a high viscosity fluid produces viscous fingering. The reverse scenario (high viscosity invading fluid) is viscously stable (boring). But what happens if we add grains to the low viscosity defending fluid? To find out, we inject water/glycerol into hydrophobic grains “submerged” in air. The bulldozing frictional instability kicks in and generates fingers through which the viscous liquid flows. The viscous pressure gradient depends on injection rate and fluid viscosity, and we shall see how increasing either produces increased viscous stabilisation of the frictional fingering pattern, taking us through a transition from a single active finger, to multiple fingers, and finally to a fully compact “spoke” pattern.

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