On the steady-state advancement of fingers and bubbles in a Hele–Shaw cell filled by a non-Newtonian fluid

Abstract

The problem of steady-state propagation of a finger or a bubble of inviscid fluid through a Hele–Shaw cell filled by a viscous non-Newtonian, including visco-plastic (Bingham) fluid is addressed. Only flows symmetric relative to the cell axis are considered. It is shown that, using a hodograph transform, this non-linear free boundary problem can be reduced to the solution of an elliptic system of linear partial differential equations in a fixed domain with part of the boundary being curvilinear. The resulting boundary-value problem is solved numerically using the Finite Element Method. Finger shapes are calculated, and the approach is verified for one-parameter family of solutions which correspond to the well-known Saffman–Taylor solutions for the case of a Hele–Shaw cell filled by a Newtonian fluid. Results are also shown for fingers with non-Newtonian fluids. In the case of a cell filled by visco-plastic (Bingham) fluid, it is shown that stagnant zones propagate with the finger, and that the rear part of the finger has constant width. The same approach is applied to finding a two-parametric family of solutions for steady propagating bubbles. Results are shown for bubbles in Hele–Shaw cell filled by power-law and Bingham fluids.