The Stokes flow defined by Eqs. (7)–(10) was solved using the
two phase flow module in COMSOL Multiphysics. A mixed formulation
was used for the velocity and pressure fields using a standard
P2/P1 interpolation (quadratic for the velocity field, linear for the
pressure). A level-set tracked the interface. The time integration
was handled using the built-in backward Euler time-dependent
solver.