Correlation functions in non-Newtonian couette flow. A group theory and molecular dynamics approach

Abstract

We develop new aspects of the statistical mechanics of non-Newtonian shear flow. The phenomena of non-Newtonian flow in the dense liquid and gaseous states are investigated by NEMD computer simulations applied to model monatomic fluids. We use mainly the PUT equations of motion for shear flow, but they are implemented in a new way. We show that in non-Newtonian shear flow there appear non-vanishing correlation functions, of the generic form, 〈v_α(0)v_β(t)〉, and 〈P_αβ(0)P_γδ(t)〉 for the soft-sphere and Lennard-Jones fluids in two and three dimensions. These correlation functions are trivially zero in the absence of shear flow. They become highly structured with shear flow and generally have a finite negative value at t= 0. They can exhibit time-reversal asymmetry, especially at large shear rate due to the vorticity term in the strain rate tensor.