Photoelastic measurement for viscous fingering in Hele-Shaw cell*

When more viscous fluid is displaced by less viscous fluid, interfacial instability is occurred with fingering patterns, which is known as Saffman–Taylor instability or viscous fingering. Understanding of viscous fingering is important because it is related to the various applications such as enhanced oil recovery. To visualize the stress field of viscous fingering in Hele-Shaw cell, we introduce the photoelastic measurement, which is noninvasive optical method. In this study, water was injected to glycerol-water mixture including cellulose nano crystals (CNC) with constant flow rate. The viscous fingering in Hele-Shaw cell was experimentally observed using a high-speed polarization camera. The viscosity ratio between water and glycerol-water mixture was changed. As a result, the fingering pattern for different viscosity ratio was qualitatively consistent with that from previous study. The retardation, which is proportional to the secondary principal stress difference, in the tip of finger and between fingers was relatively lower than that in another region.