Generalized Newtonian fluid  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 formula_2 is the shear stress, and formula_3 the shear rate. The quantity formula_4 represents an "apparent" or "effective viscosity" as a function of the shear rate. The most commonly used types of generalized Newtonian fluids are: