Fluid inertia in large amplitude oscillatory shear

Homogeneous shearing is required in sliding plate flow experiments with one plate fixed and the other oscillating. However, when fluid inertia becomes significant, the velocity gradient and the stress will not be uniform. MacDonald et al. (1969) and Schrag (1977) investigated this effect for a linear viscoelastic fluid. However, linear viscoelasticity does not describe the behavior of melts in large amplitude oscillatory shear (LAOS). Jeyaseelan et al. (1993) have shown that the Berkeley kinetic network model does accurately describe the LAOS behavior of polymer melts. In this work, the Berkeley model is solved for LAOS in sliding plate flow with fluid inertia, by numerical integration of spatially discretized forms of the governing equations. Nonlinear viscoelasticity is predicted to aggravate the effects of fluid inertia in LAOS and experiments confirm this. Specifically, fluid inertia amplifies the first harmonic and produces no even harmonics. Operating limits are presented graphically for minimizing inertial effects in LAOS experiments. Received: 2 January 1998 Accepted: 27 April 1998