Contactless generation and trapping of hydrodynamic knots in sessile droplets by acoustic screw dislocations

Helicity is an important quantity in fluid mechanics that indicates the presence of linked or knotted hydrodynamic vortex filaments. Such flow structures are not only promising elementary to study mass and momentum transfer turbulent flows but also potent analogs for other topological problems arising particle physics, liquid crystals, plasma physics. However, experimental studies knots links highly challenging due limited control over helicity generation difficult observation resulting fast-paced multiscale evolution. In this paper, we propose using acoustic streaming link filaments fluids. The method contactless, almost instantaneous, relatively insensitive viscosity. Importantly, it allows starting from quite arbitrary three-dimensional without relying on external boundary conditions. We demonstrate our approach by screw dislocation two a sessile droplet. observe inversion chirality (measured helicity) as charge increased. Combined with recent progress field synthesis, work opens window more complex topology at broader range space time scales.