INSTABILITY OF THE DISPLACEMENT FRONTS OF NON-NEWTONIAN FLUIDS IN A HELE-SHAW CELL

The destabilizing effect of the shear-thinning of a non-Newtonian flui d and its elasticity in the plane-parallel and circular displacement f ronts in a Hele-Shaw cell is investigated, as well as the influence of the elasticity of a fluid on the shape of the Saffman-Taylor ''finger s'' which are formed when primary instability develops in the fronts. The treatment is carried out separately for a pure viscous non-Newtoni an fluid and for a visco-elastic fluid (with Newtonian viscous behavio ur under steady shear flow). As a result of the multistage development of instability in the displacement of one fluid by another in a HeleS haw cell (as the how in the narrow gap between large plane parallel pl ates is traditionally called), various structures can be formed from a n individual displacement finger up to complex patterns of a fractal n ature. The form of these structures and the conditions for their forma tion are found to be sensitive to the rheological characteristics of t he fluids. (C) 1997 Elsevier Science Ltd. All rights reserved.