Molecular dynamics and Rayleigh–Benard convection

Publisher Website
Google Scholar
Abstract
A number of recent molecular dynamic studies have shown that transient convection cells can occur in hard disk systems containing as few as 5000 particles. We extend these studies, with special attention to the role of the various algorithms used to impose thermal boundary conditions. Finite‐size effects generally destabilize vortex patterns obtained with a system of 5040 atoms, using either of two different thermal boundary algorithms. Long‐lived, symmetric vortex patterns are acheived in a system of 10 200 atoms. We note, however, the fact that the class of stochastic boundary algorithms seem constrained to give vortex cells with unit aspect ratio. We also report simulations with a new cell boundary method that imposes thermal boundary conditions by making a local separation between translational and thermal energy and thermalizes groups of atoms at the same time. This algorithm represents a new hybrid between molecular dynamics and continuum methods of studying fluid behavior. Its efficiency for simulations of this kind is shown by the fact that it yields stable, long‐lived convection cells whose horizontal wave number increases as the Rayleigh number is increased. A variant of this algorithm is used to simulate convection with no‐slip boundary conditions. Implications for further research are discussed.