Frictional fingers in gravity

Pattern formation of frictional fingers in a gravitational potential

Jon Alm Eriksen, Renaud Toussaint, Knut Jørgen Måløy, Eirik Flekkøy, Olivier Galland, and Bjørnar Sandnes
Phys. Rev. Fluids 3, 013801 – Published 3 January 2018

Gravity induces parallel growth of finger structures which forms when air displaces a granular-liquid mixture. The alignment direction, which varies between horizontal and vertical, is explained by the interplay between surface tension, yield stresses, and the hydrostatic potential.

Eriksen_PRFluids2018_preprint

Gas-driven fracturing

Gas-Driven Fracturing of Saturated Granular Media

James M. Campbell, Deren Ozturk, and Bjørnar Sandnes
Phys. Rev. Applied 8, 064029 – Published 29 December 2017

Gas-driven fracturing underlies both natural and industrial processes, such as volcanic degassing, methane venting, stimulated hydrocarbon extraction, and treatment of contaminated soil. The authors show how in such a complex system the capillary, frictional, and viscous interactions together produce a range of fracture patterns, with cracks separated by a characteristic length that varies based on the conditions. Discovering how material properties and injection rate affect these patterns helps to establish a physics framework for optimizing permeability and assessing risk in gas-driven fracturing of hydrocarbon reservoirs and remediation of polluted soil.

Campbell_2017_PRAppl_preprint

Labyrinth

A labyrinth pattern self assembles as a granular suspension dries out. The material is sandwiched between to glass plates, and fluid is withdrawn through a tube and a hole in the centre of the top plate. Fingers of air sweep up the granular material – glass beads of 100 micrometer average diameter – and produce a simply connected branching labyrinth. The constant spacing between the branches represents a balance between friction and surface tension at the interface. The initial disc is 35 cm across.