Particle-induced viscous fingering

The Saffman–Taylor fingering instability arises when a less viscous fluid displaces a more viscous one inside porous media, which has been extensively studied for decades. Conversely, the invasion of a more viscous fluid into a less viscous fluid is inherently stable to interfacial instabilities. However, Tang et al. [1] first observed that the addition of particles to a viscous invading fluid can destabilize the fluid-fluid interface, even in the absence of the unstable viscosity ratio. Building on the previous observations, we experimentally characterize the particle-induced fingering patterns in a radial source flow for varying particle volume fractions and gap sizes. The onset of fingering is observed to be highly dependent on the particle volume fraction and also, to a lesser extent, on the channel gap thickness. The key physical mechanism behind this instability is the particle accumulation on the interface that stems from the shear-induced migration of particles far upstream of the interface. We model the particle-laden flow as a continuum in the quasi-steady region away from the interface, based on the suspension balance approach, and successfully validate the effects of shear-induced migration on the particle accumulation and subsequent fingering.