Hybrid SPH-MD two-phase modelling of 3D free-surface flows introducing double K-H instability

This paper studies multi-dimensional free-surface problem using a hybrid method combining the particle-based Smoothed-Particle Hydrodynamics (SPH) and atomistic Molecular dynamics (MD) techniques. In order to verify/validate the accuracy of the numerical solver, several cases including the 2D single-phase and two-phase dam break flows with dry bed, the 2D dam break flow over a layer of sand, the 3D broken dam flow, and the standard Kelvin-Helmholtz instability have been considered. After performing the particle-independence test, numerical results have been produced for several cases including the energy dissipation in 2D dam break flow with the fluidized bed, the interaction of 3D breaking dam flow with an obstacle of various heights and locations, exhaustive investigation of air particles for 2D and 3D cases, and the effect of surface tension by changing the container size and water temperature. Finally, a new version of the Kelvin-Helmholtz instability has been proposed, in which three layers of parallel flow (2 water layers and 1 air layer) including an interface and a free-surface become unstable. It is found that the water-water interface is more unstable than the air-water contact surface, and the amplified waves on the air-water interface are traveling standing waves with sharp tips.