In addition to the viscoelastic flows discussed in Viscoelastic Flows, Ansys Polyflow can also be used to model generalized Newtonian flows. The generalized Newtonian category of flow includes both Newtonian flows and inelastic non-Newtonian flows. Ansys Polyflow has a number of modeling options available for simulations of these types of flows. Several shear-rate-dependent viscosity laws are supplied, and a temperature-dependent or constant viscosity can also be modeled.

As is well known, the range of validity of the Newtonian constitutive equation is limited to low-molecular-weight, homogeneous liquids. The flow phenomena observed with polymeric fluids, for example, cannot be predicted by the classical Navier-Stokes equations. Non-Newtonian behavior has many facets. Among them are the shear-rate dependence of the shear viscosity, the presence of normal stresses in viscometric flows, high resistance to elongational deformation, and memory effects associated with the elasticity of the fluid. Non-Newtonian inelastic flows exhibit a shear-rate dependence of the shear viscosity, but the other phenomena are characteristics of viscoelastic flows.

Ansys Polyflow offers a wide variety of constitutive models for non-Newtonian inelastic fluids. It is, however, essential to be aware that none of these models leads to realistic predictions in all types of deformation of any particular non-Newtonian fluid. In many cases, the use of non-Newtonian inelastic models will capture the physics of the flow with sufficient accuracy. The only modeling issue then is to identify a suitable nonlinear viscosity function that will fit available viscosity data.

For background information about generalized Newtonian flow, see [2], [3], or [33] or any similar handbook or textbook on rheology.