Unstable oscillatory flow of non-Brownian suspensions in Hele-Shaw cells

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

Physical Review Fluids

American Physical Society

Año: 2023 vol. 8

The behavior of neutrally buoyant, non-Brownian suspensions subject to square-waveflow oscillations in Hele-Shaw cells is investigated. The velocity field across the cell gap isdetermined by tracking particles in a plane parallel to the main flow. Initially, the velocityfield of the particles is parallel to the main flow and its profile across the gap is blunteddue to a higher volume fraction of particles in the gap center; this has been confirmed bydirect estimations of the particle fraction and likely results from shear-induced migration.Velocity fluctuations, both along and transverse to the flow direction, agree reasonably wellwith previous studies. At longer times, the suspension develops an instability characterizedby the growth of a transverse velocity component that is periodic along the main flowdirection and in time. No influence of inertia on the characteristic onset time of thisinstability is observed for Reynolds numbers varying over four decades below Re = 0.4.The inverse of the onset time increases linearly with the amplitude of the oscillatory flow.The dependence of the onset time on the particle volume fraction and the gap thicknessis consistent with the characteristic time for particle migration across the gap due toshear-induced diffusion.