Large-scale molecular dynamics simulations of normal shock waves in dilute argon

Valentini, P (Valentini, Paolo); Schwartzentruber, TE (Schwartzentruber, Thomas E.)

PHYSICS OF FLUIDS, 21 (6): Art. No. 066101 JUN 2009

DOI: 10.1063/1.3149866

Large-scale molecular dynamics (MD) simulations using the Lennard-Jones potential are performed to study the structure of normal shock waves in dilute argon. Nonperiodic boundary conditions in the flow direction are applied by coupling the MD domain with a two-dimensional finite-volume computational fluid dynamics (CFD) solver to correctly generate the inflow and outflow particle reservoirs. Detailed comparisons are made with direct simulation Monte Carlo (DSMC) solutions using the variable-hard-sphere (VHS) collision model. By performing realistic MD simulations of full shock waves, this article presents a more sensitive evaluation of the VHS model parameters (via temperature and velocity distribution functions) than is possible using available experimental density measurements. In the high temperature range (300-8000 K), where the Chapman-Enskog theory supports the VHS model assumptions, near-perfect agreement between MD and DSMC solutions is demonstrated and inverse shock thickness predictions reproduce experimental measurements. In the low temperature range (16-300 K), theory predicts and MD simulation confirms that the VHS collision model becomes less valid.

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