Impact of fluid elasticity on miscible viscous fingering

•Flow experiments are performed by displacing Boger fluids with water.•Observations are compared to Glycerol displacement with water.•Elasticity is observed to retard the growth of fingers.•Dominant wave number at onset of instability is increased by elasticity.

An experimental study is performed to investigate the impact of fluid elasticity on miscible viscous fingering. Rectilinear flow experiments are performed by displacing aqueous Boger fluids (constant-viscosity elastic fluids) with water. The observations are compared to those in Newtonian fluids (glycerol solutions) of the same viscosity. Elasticity is observed to reduce the width of fingers, leading to formation of thinner and longer fingers in fully developed flow. The shielding effect is reduced due to fluid elasticity resulting in growth of multiple fingers as compared to a single thick dominant finger observed for Newtonian fluids. The dominant wave number for the onset of instabilities is observed to be higher in more elastic fluids i.e. the interface breaks down into greater number of fingers in the more elastic fluid. Data is presented to show that fluid elasticity retards the growth of fingers. Elastic effects are observed to reduce the thin film of the displaced fluid on the walls of the Hele–Shaw cells.