Numerical investigations on microfluidic multiphase flows with the open-source code Basilisk

Microfluidics enables the development of efficient lab-on-chip devices, converting lab-scale processes to microscale while using minimal reagents and allowing for precise control. At the microscale, the flow behavior is laminar, primarily influenced by viscosity rather than inertia. However, complexities can arise in two-phase flows, especially at fluid interfaces, which calls for numerical simulations for thorough analysis. In this thesis work, we used the Basilisk software to model low-Reynolds-number two-phase flows. We employed adaptive grids and the Volume of Fluid (VOF) method to accurately model the interface between the two phases. After validating the code by studying the behavior of a single drop in a duct and comparing the results with those found in the literature, tests were performed on two different configurations to characterize the flow regimes, identified as squeeze flow, drop flow and jet flow. Simulations conducted in cross-junction and coaxial setups revealed several critical factors, including the influence of the capillary number and the importance of grid resolution. In line with existing studies, it was observed that for low fluid flow rates, the regimes are characterized by larger diameter drops, which decreases with increasing flow rates. Moreover, we have also analyzed how viscosity affects the droplet generation regime and diameter. Finally, a cross comparison with OpenFOAM simulations, available within our laboratory, showed consistency between the two software, making our results more robust.