A generalized Newtonian fluid is an idealized fluid for which the shear stress is a function of shear rate at the particular time, but not dependent upon the history of deformation.
Although this type of fluid is non-Newtonian (i.e. non-linear) in nature, its constitutive equation is a generalised form of the Newtonian fluid.
Generalised Newtonian fluids satisfy the following rheological equation: where
represents an apparent viscosity or effective viscosity as a function of the shear rate.
The most commonly used types of generalized Newtonian fluids are:[1] It has been shown that lubrication theory may be applied to all generalized Newtonian fluids in both two and three dimensions.