Viscosity, couette flow simulations

Couette Flow Simulation. MD typically simulate systems at thermodynamic equilibrium. For the simulation of systems undergoing flow various methods of nonequilibrium MD have been developed (Ifl iZ.). In all of these methods the viscosity Is calculated directly from the constitutive equation. 

The nonequilibrium MD method we employed ( ) is the reservoir method (iff.) which simulates plane Couette flow. The effective viscosity Is calculated from the constitutive relation... 

The simulation value for the effective viscosity Is almost half the viscosity of the bulk fluid. According to the LADM the effective viscosity for plane Couette flow can be Identified as... 

As an example of a simation in which it is important to use an algorithm which conserves angular momentum, consider a drop of a highly viscous fluid inside a lower-viscosity fluid in circular Couette flow. In order to avoid the complications of phase-separating two-component fluids, the high viscosity fluid is confined to a radius r < Ri by an impenetrable boundary with reflecting boundary conditions (i.e., the momentum parallel to the boundary is conserved in collisions). No-slip boundary conditions between the inner and outer fluids are guaranteed because collision cells reach across the boundary. When a torque is applied to the outer circular wall (with no-slip, bounce-back boundary conditions) of radius R2 > Ri, a solid-body rotation of both fluids is expected. The results of simulations with both MPC-AT-a... 

Molecular modeling has been used to calculate viscosity using a variety of different well-developed approaches, including velocity autocorrelation [26], kinetic energy exchange [27], and simulating Poiseuille or Couette flow (also called the confined shear method) [28-34],... 

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