Instability in suspensions oscillating along narrow channels

GARCIA, A. A.; ROHT, Y. L.; GAUTHIER, G.; SALIN, D.; DRAZER, G.; HULIN, J. P.; IPPOLITO, I.

Buenos Aires

Congreso; 21th LACCEI International Multi-Conference for Engineering, Education and Technology (LACCEI 2023); 2023

LACCEI

The addition of solid particles to a fluid can changesignificantly the way it flows. This is important in severalpractical situations like landslides produced by heavy rain, wastetreatment and blood flow. In some cases, the presence of solidparticles has been shown to accelerate mixing in viscous flowsthrough small channels. In this work, we show that oscillatoryflow induces an instability characterized by particle motiontransverse to the main flow, which could help improve mixing.We perform experiments with non-Brownian spherical particles(diameter 40 μm) suspended in a viscous fluid subject to squarewaveoscillations inside a channel of rectangular cross-section(gap 1 mm, width 10 mm). Using fluorescence we visualize andtrack the particles in a plane across the gap and along the length.After a number of oscillations, we observe small but significantdisplacements of the particles across the gap. These displacementhave oscillatory and long-term drift components, both spatiallyperiodic along the flow direction. The latter may account forthe transverse deformation of a high particle volume fractionregion present in the center of the channel. Finally, we defineand characterize an onset time for this instability as a functionof the oscillation amplitude and the volume fraction.