Effects of electrohydrodynamic charge transport on surface motion and deformation at a plasma-liquid interface

We study the two-dimensional interactions between a weakly ionised single-fluid plasma and an incompressible liquid layer below it through high-fidelity numerical simulations based on the Navier–Stokes and Poisson–Nernst–Planck equations, where the conservative phase-field method has been incorporated to explore the effects of plasma-induced flow on a plasma-liquid interface. An electric potential difference is imposed across a nozzle-plate set-up, where a downward-pointing nozzle orifice serves as a source of positive ions into the overhanging plasma and a plate placed on the bottom domain boundary supports a pool of liquid above it. Consistent with experimental results, an ascending flow of liquid takes place along the vertical symmetry axis normal to the nozzle orifice, and circulation vortices emerge surrounding this liquid motion. By controlling the injection strength of ions and the magnitude of the externally applied voltage difference, unsteady undulations of the liquid surface can be clearly observed. The extent of interfacial deformation is closely related to the magnitude of the Coulomb force, which can also enhance the stabilisation of the phase interface and suppress corrugations.