When do we need attractive-repulsive intermolecular potentials?

• Main Author: Ayyaswamy, Venkattraman
• Format: Conference Proceeding
• Language: English
• Subjects: CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; COMPARATIVE EVALUATIONS; Computer simulation; COMPUTERIZED SIMULATION; COUETTE FLOW; CROSS SECTIONS; Dependence; Direct simulation Monte Carlo method; EQUILIBRIUM; INTERMOLECULAR FORCES; KNUDSEN FLOW; Matching; MATHEMATICAL SOLUTIONS; MEAN FREE PATH; MONTE CARLO METHOD; POTENTIALS; RELAXATION; Transport properties; VELOCITY; Velocity distribution; VISCOSITY
• ISSN: 0094-243X; 1551-7616
• DOI: 10.1063/1.4902583

The role of attractive-repulsive interactions in direct simulation Monte Carlo (DSMC) simulations is studied by comparing with traditional purely repulsive interactions. The larger collision cross section of the long-range LJ potential is shown to result in a higher collision frequency and hence a lower mean free path, by at least a factor of two, for given conditions. This results in a faster relaxation to equilibrium as is shown by comparing the fourth and sixth moments of the molecular velocity distribution obtained using 0-D DSMC simulations. A 1-D Fourier-Couette flow with a large temperature and velocity difference between the walls is used to show that matching transport properties will result in identical solutions using both LJPA and VSS models in the near-continuum regime. However, flows in the transitional regime with Knudsen number, Kn ∼ 0.5 show a dependence on the intermolecular potential in spite of matching the viscosity coefficient due to differences in the collision frequency. Attractive-repulsive potentials should be used when both transport coefficients and collision frequencies should be matched.