(465h) Multiphase Fluidic Oscillator in a Heart-Spade Micro-Mixer

difference mesh (1600 × 512 × 32) following the procedure of standard staggered MAC cell arrangement. All three components of the velocity field are defined on the corresponding cell faces while the pressure field, considered here as a scalar variable, is located at the cell centres, and all spatial derivatives are approximated by second-order central differences. Finally, the treatment of the interface relies on our high-fidelity hybrid front-tracking/level-set method, which uses a Lagrangian triangle interface mesh. Figure 1 depicts various flow regimes. For instance, a fast dripping regime occurs at (Qc, Qd) = (4, 0.5) mL/min, described as regular and quasi-symmetric, where the capillary pinching phenomenon occurs behind the C-shaped barrier. At (Qc, Qd) = (5, 1.5) mL/min, an irregular and non-symmetrical capillary pinching effect manifests itself far downstream after passing the C-shaped barrier. At (Qc, Qd) = (1, 2) mL/min, a Multiphase Fluidic Oscillator finally occurs. This oscillatory behaviour results from a slight delay in symmetrical interfacial breakup events occurring behind the C-shaped barrier, ultimately leading to simultaneous oscillation and pinching. This is the first observation of such oscillatory behaviour in a multiphase and microscale flow. A more laminar and
parallel regime is observed for (Qc, Qd) = (3, 1) mL/min, and the Multiphase Fluidic Oscillator regime can be described as a transition towards regimes that exhibit complex dynamics.

The vortical structures highlighted in Figure 1 (right panel) depict interesting closed recirculating zones that typically trap satellite droplets. Due to differences in flow rates between the continuous and dispersed phases, we can also observe vortical structures reminiscent of Kelvin-Helmholtz instabilities. As droplets form in the initial cell of the channel with some undergoing coalesce before entering the converging section of the cell.