DIRECT MODELING OF FLOW OF FENE FLUIDS

Direct simulations of macromolecular fluids are carried out for flows between parallel plates and in expanding and contracting channels. The macromolecules are modeled as FENE dumbbells with soft disks or Lenna rd-Jones dumbbell-dumbbell interactions. The results are presented in terms of profiles and contour plots of velocity, pressure, temperature , density, and flow fields. In addition the data for potential energy, shear stress, and the normal components of the stress tenser are coll ected. In general, an excellent agreement is found between the simulat ed profiles and the well-known flow structures, such as flow separatio n and formation of viscous eddies, indicating that micro-hydrodynamics is a viable tool in linking macroscopic phenomena with the underlying physical mechanisms. The simulations are performed in the Newtonian r egime, for medium-size systems comprising up to 3888 dumbbells. This n umber is sufficiently large to control boundary and particle number ef fects. The flow is induced by gravity. The traditional stochastic (the rmal) and periodic boundary conditions are employed. Also, diffusive b oundary conditions, which could include a stagnant fluid layer and rep ulsive potential walls, are developed. The scaling problems, which are related to the application of a large external force in a microscopic system (of the size of the order 100 Angstrom), result in extreme pre ssure and temperature gradients. In addition, the viscosity and therma l conductivity coefficients obtained from velocity and temperature pro files of the channel flow are presented. These results are confirmed i ndependently from modeling of Couette flow by the SLLOD equations of m otion and from the Evans algorithm for thermal conductivity.