Radially interrupted viscous fingers in a lifting Hele-Shaw cell

Abstract.

Viscous fingers have been produced in the lifting Hele-Shaw cell (LHSC), with concentric circular grooves etched onto the lower plate. The invading fluid (air) enters the defending newtonian fluid-olive oil, as fingers proceeding radially inwards towards the centre. The fingers are interrupted at the circular groove, and reform as secondary fingers. The effect of the grooves is to speed up the fingering process considerably and the fingers now reach the centre much faster. We explain this by comparing the variation with time, in velocity of the fingers in the normal LHSC and the grooved cells. In the normal lifting HS cell the fingers move fastest on initial formation and slow down later. Since in case of the grooved plate, the fingers reform and receive a boost in their speed each time they encounter a groove, the fingers proceed to the centre faster.