Viscous Fingering of Non-Newtonian Fluids in a Rectangular Hele-Shaw Cell

Non-Newtonian viscous fingering in a rectangular Hele-Shaw cell was studied. Compressed air was injected into the cell filled with a more viscous fluid. For the more viscous fluids, glycerin was used as a Newtonian fluid, and aqueous solutions of carboxymethylcellulose (CMC) and polyacrylamide (PAA) were used as non-Newtonian fluids. The growth and the structure of viscous fingers were analyzed. The shear-thinning viscosity of the polymer solutions made the 'shielding' effect strong. When the 'shielding' appeared strongly, the fingers formed a branched structure. In the PAA solution, the change in the finger pattern, a sudden growth of thin fingers from a wide finger-tip, was observed. It was supposed that stretch-thickening elongational viscosity and the shear-thinning viscosity were related to this phenomenon.