01. Experimental/Computational Fluid Dynamics

In this study, we observed the free surface shape of concentrated particle suspension in a Hele Shaw channel and investigated the generation behavior of particle-induced viscous fingers accompanying with the changes in particle concentration during flow. The Hele-Shaw cell used in the experiment was composed of two transparent acrylic plates (200 mm square) sandwiched between a 1 mm spacer. The sample fluid was supplied to the Hele-Shaw channel from the center of the flow channel by compressed air. The sample fluids were a mixture of transparent acrylic spherical particles (φ135-150 μm) and an aqueous solution of glycerin 74.4 wt.%, and the particle concentration was 50 wt.%. The experiments were conducted by changing the supply pressure and recording the flow patterns using a video camera. The results in visualization experiments showed that after the supply of the sample fluid, the interface shape spread concentrically, but then unevenness of interface was observed. In particular, the region of high particle concentration called a particle band appeared at the outer circumference of interface. In addition, the fingering patterns were confirmed in the inside of liquid interface. The shape of the fingering of interface represents a boundary of particle concentration, and the growth of the fingering was confirmed over time. Furthermore, it was predicted that the occurrence of the fingering phenomenon was related to change in shear viscosity caused by local changes in particle concentration.