Complex fluid-dynamical phenomena modeled by large-scale molecular-dynamics simulations

We carried out large-scale molecular-dynamics simulations of the classical Rayleigh-Taylor (RT) phenomenon in a Lennard-Jones molecular liquid. We have observed from these simulations, involving 10(6)-10(7) particles, the development of hydrodynamic instabilities from two different kinds of interacting particles. A free surface is introduced by deploying an overlying void. For a box with a dimension up to about 1 mu m and two layers having different particle sizes, the fingering type of instability is observed as a result of oscillations caused by the gravitational field. In this gridless scheme, surface waves can be captured self-consistently. For equally sized particles, a spontaneous "fluctuation driven" mixing with a long start-up time is observed. These molecular-dynamics results suggest the possibilities of upscaling the RT phenomenon. For conducting these numerical experiments, which require at least similar to 10(5) time steps, a single simulation would require 100-200 Tflops of massively parallel computer power. (C) 1998 American Institute of Physics. [S0894-1866(98)01606-X].